Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd eeeaeo erydgnrt O,adteeeit oKkl tutrlfruafrti yeo system of type this for formula structural Kekulé no exists there and [3]a]. MOs, degenerate nearly or degenerate π Introduction 1 State Ground Open-Shell an with Polycyclic Wu Jishan / Das Soumyajit GRUYTER DE hscneti free. is content This Berlin/Boston. GmbH, Gruyter de Walter 2017 © Wu Jishan (e.g., drawn be of can state formula structural ground Kekulé m the However, one species. least triplet at singlet and active as gener- reduced QDM)- magnetically singlet character the the still diradical to is of singlet due species population strong signal such the to (ESR) increase moderate to with believed PHs is electron region. different broad shared occupies interaction, a small anti-ferromagnetic show a through ally with coupled space paired producing weakly electrons the fashion, being the of antiparallel all electrons, has parts or these species, parallel of molecular a in pair as a orient mono- diradical, standard Singlet but of can the species. 1) spins diradical + by singlet two (2S or permitted multiplicity diradicals, biradical spin number for triplet The whereas the MOs. near-degenerate a doublet, than two occupy is or less electrons radicals biradical two bond the perfect one and the valence have of limit, that toas rule dissociation molecules is referred even-electron bondlimit, bond stable are the state Ina Diradicals intermediate in Any while regime emerges. configuration dissociation toLUMO. exists open-shell bond character pure HOMO the diradical from to no configuration regime excited bond closed-shell, doubly stable i.e., of the weight from or to nature the diradical bond tends increasing in character either through variation diradical by a un- [4], classified causing representation more be reduced, (HOMO) (MO) orbital gets or can molecular orbital ground occupied molecule one highest molecular the a the of (R) in as in existence spin-restricted increase molecule (radicals) neutral the the electrons in In to unpaired electron [3]. due unpaired two biradical an of state of Existence ground comprised [2]. is open-shell state PH show Monoradical or [1]. state electrons paired ground closed-shell a form DOI: Cnuae oyylchdoabn Ps a ihraccommodate either can (PHs) hydrocarbons polycyclic -Conjugated qioiehn ( -quinodimethane 10.1515/psr-2016-0109 stecrepnigauthor. corresponding the is o qioiehn ( -quinodimethane m QM-ae H,Fgr () samlclrseiswt w lcrn cuyn two occupying electrons two with species molecular a is 1(a)) Figure PHs, -QDM)-based o QM-ae H,Fgr ().O h te ad uebrdclP (e.g., PH biradical pure a hand, other the On 1(a)). Figure PHs, -QDM)-based – oetuocpe oeua ria LM)gap (LUMO) orbital molecular unoccupied lowest π eetosi h odn riasto orbitals bonding the in -electrons hsclSine eiw.21;20160109 2017; Reviews. Sciences Physical “ diradicaloid – rpe nrygp which gap, energy triplet p qioiehn ( -quinodimethane ” (diradical-like). p 1 - Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd oprdto compared hrce rsn rmtercvr fteaoaiiyo h eta ezni igo h epciequinoidal respective the of ring benzenoid Comparatively, central state. the ground of the in the subunits, of recovery the from arising character C eventually can a that break minimization to energy required net aromatic- energy of A recovery structure). the the is (quinoidal surpass structure rings such for non-aromatic force consecutive driving Jahn from the [5]b], the ity diradicals by of formation caused the ground for geometry singlet 1(b)) its square (Figure in delocalized shape rectangular of a prefer instead derivatives cyclobutadiene state that found was non-bonding it degenerate later two fact, In occupy elusive. electrons two as are diagram categorized which MO be MOs their can cyclobutadiene to according parent like diradicals molecules delocalized Antiaromatic as favorable. highly normally are gained is oligothiophene. quinoidal of example an as shown is proaromaticity of concept The (b) form. biradical h otbsc e oefl praht eeaeadrdcli Hi oebdan embed to is PH diradicaloid a a generate into to approach powerful, yet basic, most The Hydrocarbons Polycyclic Open-Shell Quinodimethane-Based 2 state. where [13]: equation following the using by determined denoted be is also which can eventually character, character and diradical diradical the Experimentally, character the LUNO. therefore, diradical the that character; the implies diradical in This the increase diradical. on where pure the occupation depending a with NO for increase 2, the 1 should and molecules, LUNO approaches singlet 0 the open-shell between of the value number in (un- intermediate 0 whereas occupation an or shell, (occupied) be closed 2 for can numbers model 0 occupation number two-orbital is (NO) atwo-electron LUNO orbital for the natural So the [4], has occupied). Nakano molecule by closed-shell simplified state As ground character. diradical usingthe theunrestricted of extent approach, the inBS as (LUNO) spincontamination to discard [11] Hartree technique spin-projection with ified Hartree restricted the using ESR tion the as report impurities. the monoradical in some given was from structure come electronic also state may ground signal the with regarding signal conclusion ESR clear of no presence although the and signal that appar- [9] NMR of derivative Absence sharp nonacene crystalline and HOMO isolated clear first low showed the from ently for except evident higher-order (as already of observations states signal) experimental (NMR) Interestingly, ground to [8]. found closed-shell state were dodecacene the ground than their established larger in acenes character and polyradical dodecacene, to singlet diradical exhibit from of pop- lengths largely amount chain is et large all (SOMO) Hachmann for Later, a orbital singlet [7]. molecular with edges occupied bandgap singly zigzag the nonzero the and on a state ulated method, possess ground UB3LYP/6-31G* open-shell , singlet singlet (BS) than for a broken-symmetry larger in energies character acenes, the calculated that the using shown that by was implying Re-optimization it oligoacenes, high. higher unbelievably all are and states hexacene as small et as Bendikov oligoacenes rings. fused linearly of aromatization of duetothe result [6]. a rings as character species thiophene diradical active the unquestionable the magnetically on excited of (rt)) reports temperature first (room the thermally constitute of 6QT population the and whereas 5QT shell, the closed of are spectra oligomers ESR tetracyano-quinoidal-thiophene proaromatic smaller The state. ground 1: Figure 2 and spectra, (TPA) absorption rmtct sakycnetfrceityi h lcrncgon tt,adratosi hc aromaticity which in reactions and state, ground electronic the in for concept key a is Aromaticity hoeial,drdclcaatri siae yacmlt ciesaesl-ossetfed(C)calcula- (SCF) field self-consistent space active complete a by estimated is character diradical Theoretically, consisting PHs of class a to belong and graphene of fragments one-dimensional as regarded be can Acenes π a n Wu and Das y E cnuae rmwr.Ti prahhsbe oi fitneitrs u oterihrn diradical inherent their to due interest intense of topic a been has approach This framework. -conjugated – S a tutrsof Structures (a) scoe hl and shell closed is 0 = okwv ucin[2 a eieteocpto ubro h oetuocpe aua orbital natural unoccupied the lowest of number occupation the define can [12] function wave Fock 1 u,S 1 p g QMdrvtvs Unlike derivatives. -QDM and “ spin-up E S 2 g,S p -QDM, ” 1 – g nard aigte togyratv pce n hstersnhssi highly is synthesis their thus and species reactive strongly them making unpaired, UOgpo . Vwihi rtro o h rgno iaia hrce nPH. in character diradical of origin the for criterion a is which eV 1.2 of gap LUMO orsodt h nryo h oeteeg ek nteoe n two-photon and one- the in peaks energy lowest the of energy the to correspond E y T o – QMadtersnltdrdclrsnnefrs(euéform); (Kekulé forms resonance diradical singlet their and -QDM 1 spr pnselbrdcl,cnb eie yteocpto ubrof number occupation the by defined be can biradical), open-shell pure is 1 = okadtocniuainSFcluain.AB prah[0,latermod- [10], ABSapproach calculations. SCF two-configuration and Fock u,S = 푦 1 g orsod oteeeg a ewe h rpe n h ige ground singlet the and triplet the between gap energy the to corresponds 1 − o – and - ⎷ √ √ √ obebn stekyi eeaino noe-hl diradical open-shell an of generation in key the is bond double C 1

l hwdta h BLPwv ucinbcmsusal for unstable becomes function wave RB3LYP the that showed al. − o QMdrvtvssc speaee[4 r xrml reactive extremely are [14] pleiadene as such derivatives -QDM ⎝ ⎜ ⎛ p QM the -QDM, 퐸

l losoe httegon tt flna oycnsis polyacenes linear of state ground the that showed also al. 푆 1 푢,푆 퐸 1 푔 푆 2 퐸 − 푔,푆 g 1 m e 푇 푔 QM(i.e., -QDM 1 .00frnncn eiaiewr reported, were derivative nonacene for 2.0060 = 푢,푆 – 1 elrefc 5.I h raoai concept the proaromatic In [5]. effect Teller 푔 ⎠ ⎟ ⎞ 2 , m xlln iaia)cno aea have cannot biradical) -xylylene 1 ula antcresonance magnetic nuclear H o QMor -QDM m QMi t triplet its in -QDM p QMsubunit -QDM y EGRUYTER DE (0 ≤ y ≤ 1 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd ino obe ooaia pce n iesrcueERsetu fatpcltiltsaewhichwas state triplet ofatypical spectrum oligomer/polymer superposi- give ESR a to gave fine-structure polymerize stage a to intermediate and conducted at compound species was sample to monoradical the measurement attributed of doublet ESR freezing a (VT) rapid of temperature and Variable tion step [18]. oxidation 3) chemical (Figure the vertexes monitor derivative three et the reactive Nakasuji on highly groups [17]. a state obtain neutral to an chloranil in synthesize state to ground Clar triplet by attempt unsuccessful An 2.2 2: Figure of state triplet accessible thermally to due observed singlet was reduced temperatures a higher of at signals because the an endoperoxide of broadening affording and air rt vertically in at the reactive prepare quite to be conducted to was reported approach synthetic similar A ring. extended naphthalene inner the to further structure distribute calculation Kekulé shift to lead chemical can Nucleus-independent respectively. 0.21, of character that and supports diradical 0.33 singlet was The theory. scheme by Yamaguchi supported also was which contribution, 2). (Figure rings five-membered o the on unaffected bromide located The mesitylmagnesium solid. mainly adding by sites sites, diketone reactive radical the the with protect to kinetically state, to introduced ground were groups the Clar Mesityl in additional one color) of recovery gray to due in contribution resonance diradical show could which et Tobe 2.1 ( open-shell triangulenes generates as ofan such benzenoid polycyclic systems PH.Embedding planarized a non-Kekulé into into subunit classified ical is thus and structure quinoidal closed-shell GRUYTER DE iue3: Figure in QMcr,a e rsa tutr nlss niaealresinglet large a indicate analysis, structure crystal per as core, -QDM 8 1 oprdto compared (0.33). o m QMEbde Diradicaloids -QDM-Embedded

l eotd[5 h ytei n rsalgahcsrcueo nindeno-[2,1- an of structure crystallographic and synthesis the [15] reported al. Xlln-ae Systems-Xylylene-Based tutrsadsnhsso Tobe of synthesis and Structures ytei fNakasuji of Synthesis o QMderivative -QDM 5 swal nirmtca euto the of result a as antiaromatic weakly is 3 5 oafr h diol the afford to h index The . 1 M pcr of spectra NMR H 11 rehdoabnwt he-odrtto axis. rotation three-fold with hydrocarbon true a , ’ – tri- s 8 rpe nrygpof gap energy triplet 2 y ieinfra vide hc a ofre yXrycytlorpi nlss[6.Ti opudis This compound [16]. analysis crystallographic X-ray by confirmed was which hc a lohv w iaia eoac om n h pndniymay density spin the and forms resonance diradical two have also can which a siae ob .3wihwscnieal agrwe oprdt that to compared when larger considerably was which 0.63 be to estimated was tert 4 btltinueederivative. triangulene -butyl hc ntetetwt i(Iclrd gave tin(II)chloride with treatment on which ’ s 12 ,wt ag pndniisa h desites. edge the at densities spin large with ), o QMderivatives. -QDM . 5 thge eprtr n infcn odlnt lento in alternation bond-length significant a and temperature higher at – .6ka mol kcal 7.46 m xlln eiaie ragun,wsepandb the by explained was triangluene, derivative, -xylylene

l rae dihydrotriangulene a treated al. as idcn oey h vertical The moiety. -indacene 11 9 lhuhbigpoetdb bulky by protected being although , Fgr ) Compound 2). (Figure – 1 niaiga nacddrdclcharacter diradical enhanced an indicating , – rpe nrygpwt ml diradical small with gap energy triplet 11 shgl ecieadtnsto tends and reactive highly is 5 sasal,purple-colored stable, a as a 1 furn ( ] π 8 and cnuae rpe PH triplet -conjugated π hwdsapsignals sharp showed 10 etninof -extension ’ ett(highlighted sextet s 5 rcro with precursor m siae ythe by estimated xlln birad- -xylylene a n Wu and Das 1 derivative ) tert o -QDM -butyl p 5 3 - Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd infcn iaia otiuin( contribution diradical significant C(sp the bond of of lengths bond the showed indeed ysis it ewe obe n igebn aus(.2 n .7 ) niaigsgiiatdrdclcontribution diradical significant indicating Å), 1.372 and (1.420 values single-bond and double- the between of diate part central the in distance derivative bond The [26]. polymerization instantaneous underwent linearly In mol contrast, diphenoquinodimethane [25]. kcal tetracyano-substituted 16.1 state the be ground derivative, to closed-shell found a stable theoretically was confirming thereby state line state, triplet any ground the or heating as on spectrum spectrum NMR ESR in the broadening in characteristics ground diradical no the exhibited also in naphthoquinodimethane), found fluoreno[4,3- are A characteristics [24]. open-shell indeno[1,2- no Similarly, [23]. although state materials, electron-transporting Indeno-[1,2- [22]. as character promise diradical negligible with dis- systems be matic to heptazethrenes, and (IDPL) later. indacenodiphenalene cussed like bis(phenalenyl)s the include examples typical the fused a stabilize into help can (TCNQ, centers), cyanoquinodimethane (radical sites terminal the in tion in Thiele sites methylene ble terminal the of Substitution 2.3 5: Figure singlet the However, indicating temperature, mol state. decreasing ground with decreased open-shell intensity singlet signal a ESR The species. triplet active thermally the rt of 15 isomer mesityl-substituted the Indeed, of form resonance diradical the a in energy stabilization resonance More indeno[2,1- 5). (Figure forms resonance open-shell 4: Figure 4 reac- a to leading other each to parallel derivative aligned high-spin at methyltetrahydrofuran spins protected kinetically two A with of 4). nation form (Figure biradical biradical open-shell triplet tive its in drawn be rtcinfra es n a [19]. day one least at for protection ]fluorene (2 sextets in closed shell vs. 3 sextets in open shell) is supposed to increase its diradical character. increase to supposed is shell) inopen sextets vs.3 shell inclosed (2 sextets ]fluorene n usqetrdcino h diol the of reduction subsequent and An w ahhln nt rde yan by bridged units naphthalene Two – 1 1 a eaieyhge oprdt h hoeia au of value theoretical the to compared higher relatively was , M inladol ra M inl tlwtmeauedw to down temperature low at signals NMR broad only and signal NMR H p a n Wu and Das m QMEbde ytm n Its and Systems -QDM-Embedded ytei fTobe of Synthesis Wu of Synthesis xlln nt noprtdit indeno[2,1- into incorporated unit, -xylylene ’ 13 19 hydrocarbon s p 2 b ) QMcr 136ad149Å Fgr )[1.Eeto-ihrwn yn C)gop,a the at groups, (CN) cyano Electron-withdrawing [21]. 6) (Figure Å) 1.449 and (1.346 core -QDM furn 1sxe ncoe hl s rmtcsxesi pnsel comparedtoindeno-[2,1- open shell) in sextets aromatic vs.3 shell inclosed (1 sextet ]fluorene π p sn ihu ispoyaieadsbeun xdto ftedainwt oiei r 2- dry in iodine with dianion the of oxidation subsequent and diisopropylamide lithium using – ihfu hnlpoetda h emnlmtyee(Tschitschibabin methylene terminal the at protected phenyl four with cnuae Hfaeokhsbe nefcetapoc ognrt ige iaiaod,and diradicaloids, singlet to generate approach efficient an been has framework PH -conjugated QMebde neoloeecneeshv enrpre stpclcoe-hl antiaro- closed-shell astypical reported been have congeners indenofluorene -QDM-embedded C(sp 2 odi ezn 13 )adteC(sp the and Å) (1.39 benzene in bond ) c furn ( ]fluorene ’ s ’ pnselindeno[2,1- open-shell s m 18 – xlln-meddhpaeheeisomer. heptazethrene -xylylene-embedded 8C This 78°C. u oaqiodlcoe-hl rudsaewt togbn-eghalterna- bond-length strong a with state ground closed-shell quinoidal a to due c 29 21 ]fluorene eiaie opiigo laterally a of comprising derivative, ) y ssal n omrilyaalbe noprto fa of Incorporation available. commercially and stable is ) .8 ngon state. ground in 0.68) = nsitu in 17 16 rprdb diino eiymgeimboiet h diketone the to bromide mesitylmagnesium of addition by prepared , undott easnltdrdcli h rudsae[0.Absence [20]. state ground the in diradical singlet a be to out turned , 28 m π eeae rpe iaia a essetat persistent was biradical triplet generated xlln oeycno aeaKkl tutr n a only can and structure Kekulé a have cannot moiety -xylylene Etne Derivatives -Extended a eiaiewsas on ob lsdseli h rudstate ground the in shell closed be to found also was derivative b 147Å and Å) (1.437 ]fluorene. p QMb orpey rusrsle nteraoal sta- reasonably the in resulted groups phenyl four by -QDM b furn rmwr,cnb rw nobt closed-and both into drawn be can framework, ]fluorene – rpe nrygpetmtdexperimentally, estimated gap energy triplet 2 b ) 141Å r iia n i ewe h lengths the between lie and similar are Å) (1.431 – C(sp 22 – .6ka mol kcal 2.46 a enrpre ob eyratv and reactive very be to reported been had , p b QMdrvtvsad ned h tetra- the indeed, and, derivatives -QDM 3 ]fluorene ) bond in fluorene (1.468 Å), supporting (1.468 fluorene in bond ) π -extended 14 27 – – 1 3Cidct h xsec of existence the indicate 93°C a yteie ydeproto- by synthesized was eiaie aesontheir shown have derivatives -a rsalgahcanal- crystallographic X-ray . ’ yrcro)i interme- is hydrocarbon) s p QMacietr (2,6- architecture -QDM – 8Cudrnitrogen under 78°C π π – 1 -extended -extended bv h singlet the above p QMmoiety -QDM EGRUYTER DE – p p . kcal 4.2 -QDM -QDM Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd ettrnscnb eoee rmacoe-hl uni oa pnseldrdclform. aromatic diradical more open-shell because an simply to in units, quinoid character closed-shell proaromatic the diradical a of from that number recovered be increasing newobservation can the rings to a with sextet emerge should lead PHs indeed, planar findings, These state. ground more the 26 whereas [28], state terphenoquinone ground and system, closed-shell quinoidal a aiasi h rudsae h nacddrdclcaatri h ihrodroioesi u otelarge the to due is oligomers higher-order bi- the coupled in weakly character become diradical hexamer enhanced and The pentamer state. ground and the diradicals, in singlet radicals open-shell closed are a possesses tetramer monomer and the trimer length, chain the of extension upon dibromo-oligomers the from coupling Takahashi radicaloids 8: Figure quinoidal closed-shell a as behaves it thus transistors. effect and field 8) ambipolar (Figure in form semiconductor as resonance used diradical was its and hydrocarbon in drawn be can precursor rings diol the corresponding at the fused from simultaneously synthesized being groups indene two of comprised 7: Figure HOMO large relatively broadening a line and NMR an at causing signal species ESR triplet an excited and thermally of population the suggesting measurements, singlet Compound [31]. 7) oligo-( tetracyano-substituted stable thermally and air 6: Figure in observed was character diradical enhanced more A bon [21]. state ground the in GRUYTER DE 3]aeERatv ohi h ouinadsldsae,idctn infcn iaia otiuininthe contribution diradical significant indicating states, solid and solution the in both active ESR are [30] uet Wu diindeno[1,2-b:20,10- closed-shell A et Nakamura 20 – Fgr )ta hwda S inltpclfrtiltseisa 5 2] h biphenoquinone The [27]. K 153 at species triplet for typical signal ESR an showed that 6) (Figure rpe a f21 clmlwsetmtdb uecnutn unu nefrnedvc (SQUID) device interference quantum superconducting by estimated was kcal/mol 2.12 of gap triplet ytei fdiindeno[1,2-b:20,10- of Synthesis Nakamura of Synthesis of Examples

l a eeoe eiso ercaotriae,quinoidal tetracyano-terminated, of series a developed had al. 37 opiigo extended of comprising

l sdplaimctlzdTkhsiculn nteiodo-derivatives the on coupling Takahashi catalyzed palladium used al. 33 π g -extended e ipae eprtr-eedn raeigo its of broadening temperature-dependent displayed .0 t30K ncnrs,tecoe-hl compound closed-shell the contrast, In K. 340 at 2.003 = – ’ unia oligo-( quinoidal s UOeeg a 15 V oprdto compared eV) (1.58 gap energy LUMO p QM and -QDMs para p n n QMfaeok(iue9 3] hs lgmr eesnhszdby synthesized were oligomers These [33]. 9) (Figure framework -QDM ] ]perylene etne quaterphenoquinone -extended p QMebde PHs. -QDM-embedded para 35 36 peyeevnln)diradicaloids. vinylene) -phenylene 35 n t pnselform. open-shell its and 34 olwdb xdto with oxidation by followed ossigaTschitschibabin a consisting , para ytetn i(Iclrd 3] oetaaoai sextet aromatic extra No [32]. tin(II)chloride treating by 24 peyeevinylenes) -phenylene losoe togbn eghatraini the in alternation length bond strong a showed also peri – hl unia tutr hl h dimer, the while structure quinoidal shell and - 33 N 1 anltdprln N)bsddi- (NP)-based perylene -annulated M pcrmadaqiesmall quite a and spectrum NMR H 25 10 eV). (1.02 β oiino eyeecr was core perylene a of position - 2]adquinquephenoquinone and [29] 31 π 31 etne Müller -extended p xiie hr M signals NMR sharp exhibited clrnl twsfudthat found was It -chloranil. ’ and yrcro framework, hydrocarbon s 33 30 epciey(Figure respectively , and a n Wu and Das 32 π ’ -conjugated hydrocar- s ogenerate to 23 is 5 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd a eatiue otercvr ftoadtoa rmtctipeernsi h iaia eoac forms resonance diradical 11). the (Figure in connections thiophene-rylene the rings thiophene around aromatic flexibility additional conformational two the of with recovery together the contribution to diradical attributed larger be The can [35]. respectively 0.93, to compared and 0.81 as estimated for character diradical with state )and 1) = 10: Figure role critical a plays cores molecules. rylene ofquinoidal the between configuration angle electronic dihedral theoreti- the the character, fine-tuning that diradical in conclusion valuable the a ( although to smaller form, leads quite comparison open-shell be the to The in found units mechanism. was cally, naphthalene polarization aromatic double-spin six a of via recovery spins two trimer the fused of coupling antiferromagnetic dimer intramolecular perylene unfused the to contrast In ( hexarylenequinodimethane and 9: Figure unitsinthe perylene approaches character quinoidal diradical ofthe the hexamer. hence and and stability, pentamer more the ofaromaticity gain for to 1 the oligomers thenearly recovery to longer structure the quinoidal Inaddition, helps rigid form the diradical from form. release diradical strain a flexible causing more NPs neighboring the between repulsion steric 6 noprto foetipeeui ewe h yeeadtedcaoehln iei closed-shell in site dicyanomethylene the and rylene the between unit thiophene one of Incorporation ( tetracyano-quaterylenequinodimehtane planarized release, of strain influence the minimize To 43 si gemn ihtesrne S inladsalsinglet small and signal ESR stronger the with agreement in is a n Wu and Das ytei n tutrso ercaoqiodlN oligomers. NP tetracyano-quinoidal of structures and Synthesis 40 ytei n tutrso ue ercaoqiodlrylenes. tetracyano-quinoidal fused of structures and Synthesis ( m – 40 .1ka/o for kcal/mol 4.71 )cnraiytr nterdrdclsae,making states, diradical their on turn readily can 0) = ( m )hsa pnselsnltdrdclgon tt u otesaiiaintruhthe through stabilization the to due state ground diradical singlet open-shell an has 1) = 42 40 eemndb QI esrmns uhasrn iaia contribution diradical strong a Such measurements. 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( forms state resonance diradical ground respective closed-shell their a favor should which 12: Figure while in site, dicyanomethy- amine and the (donor) at benzo-1,3-dithiol-2-ylidene stituents [36]. by et 12) substituted (Figure Wu respectively sites systems, (acceptor), terminal lene such similar two achieve with with systems to oligomers singlet order NP open-shell In ascom- symmetric [4]. or hyperpolarizabilities size systems second conjugation and closed-shell first asymmetric static conventional of to enhancement pared further exhibit could characters diradical 11: Figure GRUYTER DE ah opigfo h orsodn rm-adbno1 -iho--lsbtttdoio r( or oligo- 3-dithiol-2-yl-substituted benzo-1, and bromo- perylenes) corresponding the from coupling hashi odrdslsdta h S nest erae stetmeauedcesd niaigta both that indicating decreased, temperature – the as decreased with intensity state 48 ESR solution the and that solid disclosed in powder both spectrum broad a played series higher the (e.g., contrast, In state. ground shell of spectrum h rudsaeadpyia rpriso h ooe ny u ninfcn ntedmrand trimer. the dimer on insignificant but on only, effect monomer significant the a of has properties polarity thus solvent physical and chain result, and increases, the a state character of As ground diradical extension dependant. the solvent the an less while with become decreases that properties the found character physical was zwitterion of their it the charges and of Hirshfeld calculated contribution the were the derivatives, regions length, terminal the diradical/ionic the in flexible and character more units to transfer NP back charge central relax intramolecular to tends the which evaluate structure, To quinoidal form. rigid the in units NP the ( between of monomer for increase closed-shell abrupt nm from This 1,900 character response. at GM diradical open-shell 670 of pure and nearly enhancement GM to the 660 for about reasoned of values was the observation to push compared the nm 1,500 in monomer at The state length. ground conjugation the same to the form pull diradical the than the smaller of contribution The length. .1 clmol kcal 0.114 46b aea pnselsnltgon state. ground singlet open-shell an have nuotoo praht tblz h Tschitschibabin the stabilize to approach unorthodox An et Nakano – 0°) mligteroe-hl iaia rudsae codnl,ERmaueet nbt dis- both on measurements ESR Accordingly, state. ground diradical open-shell their implying 100°C), upesdtesrn grgto bevdin observed aggregation strong the suppressed ytei n tutrso push of structures and Synthesis QDMs. rylene capped tetracyano-thiophene of structures and Synthesis 45 46b olwdby followed ,

l,tertcly rdce htteaymti pnselsnltsseswt intermediate with systems singlet open-shell asymmetric the that predicted theoretically, al., – 1 nCDCl in for – 47 ultp framework type pull and 3 47 xiie hr ek tr n vna lvtdtmeaue ofrigisclosed- its confirming temperature, elevated at even and rt at peaks sharp exhibited p clrnltetett nuecmlt eyrgnto.The dehydrogenation. complete ensure to treatment -chloranil 48 ( y epciey niaiga nrae iaia hrce ihicesn chain increasing with character diradical increased an indicating respectively, , .9)and 0.899) = 47

y l,t eeaetettaeznuae hydrocarbons tetrabenzannulated the generate to al., rmmnmrt ie sbcueo h esnbylresei repulsion steric large reasonably the of because is dimer to monomer from and – ultp unia Poligomers. NP quinoidal type pull 48 37 Δ r h ihrodraaous h uk ,-icoyoy group 2,6-dioctoxytolyl bulky The analogues. higher-order the are 46a 46b E 48 ( S-T n ( )( 2) = and y 47 aeamxmmTAcosscinvleo bu ,0 GM 1,000 about of value cross-section TPA maximum a gave auswr siae ySUDt be to SQUID by estimated were values 50-CS .9)ta osntbnfttennlna pia (NLO) optical non-linear the benefit not does that 0.995) = and 46b – 46a .4 clmol kcal 0.341 and 48 ersn h mletdrvtvswt ifrn sub- different with derivatives smallest the represent hi ytei a civdb dctlzdTaka- Pd-catalyzed by achieved was synthesis Their . hwdNRslneee ttelwtemperature low the at even silence NMR showed 52-CS ’ yrcro sbnanlto ftecentral the of benzannulation is hydrocarbon s

l eotdtefrtpush first the reported al. g e .07 h TERmaueet nthe on measurements ESR VT The 2.0017. = stoaoai Clar aromatic two as ) – 1 and ) 37 ( n – ultp ytm sslightly is systems type pull )( 3) = 47 50 and and – .0 clmol kcal 0.107 – 50 – 48 52 .4 clmol kcal 0.348 ’ ultp quinoidal type pull ett r otin lost are sextets s and epciey This respectively. , 1 dp contorted a adopt and H a n Wu and Das 52 N Fgr 13) (Figure -annulated y 13 0.123) = NMR C – 1 47 – with ) 1 and and 7 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd eae akt h oesal pnselform. open-shell stable more the to back closed relaxed the isolate to singlet attempt a An with surements. signal of ESR state strong ground of biradical presence and triplet signal the hand, other the On mol kcal (22.7 barrier lydcydt h lsdselgon state ground closed-shell precursor the diol to the decayed of ally reduction by obtained chemically was which state compound Butylphenyl-substituted airadpyia rpris(iue1) ramn of Treatment 15). (Figure by properties form physical crystalline and the havior in isolated and prepared been Kubo have derivatives [40] quarteranthene and [39] Teranthene Anthenes 3.1 14: Figure zigzag the onto groups the imide at electron-withdrawing substitution of by or introduction edges by achieved was bisanthene character closed-shell an- diradical neighboring ( open-shell between Clar bisanthene remarkable bonds ( of called single a quarteranthene recovery molecules three periacenes), graphene-like by through for together extended stabilization fused generates 2 and units extended thryls > bandgap is m form. narrow conjugation resonance and a the diradical anthenes from As the for originates 14). 0 (Figure which > edges emerge (n zigzag may point extended certain with edges a armchair to and zigzag both ing and Anthenes and Anthenes Open-Shell 3 13: Figure the of stability thermodynamic better The state. ground for the in state in state biradical ground ground triplet quinoidal diradical coupled closed-shell weakly a a as supported regarded calculation theoretical with assisted ( structures anthryl diradical the orthogonal among ing hindrance steric larger a with geometry 8 ’ ru,tu loigadtie netgto ntergon-tt oeua tutr,ceia be- chemical structure, molecular ground-state their on investigation detailed a allowing thus group, s a n Wu and Das Aswt ohzga n rcaregsadterdrdclform. diradical their and edges armchair and zigzag both with PAHs Wu ’ erbnoTcishbbntp PHs. type tetrabenzo-Tschitschibabin s peri n fsdaee praee)aercaglrplcci rmtchdoabn PH)compris- (PAHs) hydrocarbons aromatic polycyclic rectangular are (periacenes) acenes -fused 2, = – 1 ) for the transition from the orthogonal diradical form to a butterfly-like quinoidal form. quinoidal butterfly-like a to form diradical orthogonal the from transition the for ) m )ads n lsdselbsnhn sa ntbemtra n tblzto of stabilization and material unstable an is bisanthene Closed-shell on. so and 1) = 52 can be credited to the efficient spin delocalization on the fluorenyl units. 4- thefluorenyl on delocalization spin efficient the to credited be can meso pstoswt rlo lyegop [38]. groups or aryl with -positions 50-OS 50 Peri aosaclosed a favors – and FsdAcenes -Fused hl omof form shell 50-CS 52-OS ihahl-ietm f45mnoecmn h ag energy large the overcoming min 495 of time half-life a with oefvrbe hruheprmna investigation experimental thorough A favorable. more ) – – rpe nrygpo .3 clmol kcal 0.334 of gap energy triplet hl rudsae(i.e., state ground shell 52 53 52 (i.e., peri ih2mstlansu rmd ntepresence the in bromide 2-mesitylmagnesium with (i.e., hdoes hc ol aetecorrespond- the make could which -, 52-OS 52-CS a ofre yteasneofNMR absence the by confirmed was ) 49 n a alda h nemdaequickly intermediate the as failed was ) n h iaia xie tt gradu- state excited diradical the and , 0, = m 50-CS ) eatee( teranthene 1), = n iaia excited diradical a and ) – 1 50 rmSUDmea- SQUID from while n 1, = ’ EGRUYTER DE ettin sextet s 52 m a be can 1), = tert - Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd diinlCa ett,rsetvl,i t iaia eoac om ec h iaia om otiuealot a contribute forms diradical the hence state. form; four ground resonance and their diradical three to its include both in respectively, quarteranthene sextets, and teranthene the Clar contrast, additional to In favored. due is pairing energy electron destabilization so pensated, the therefore, sextets; additional two ae ntehmdsi tblzto nry s~15ka mol double kcal a ~21.5 of benzene, is of loss energy, energy formal stabilization stabilization C the aromatic [40]. homodesmic between The quarteranthene Kubo. the balance by for energy on explained 0.91 well the based was and of stabilization teranthene terms aromatic diradical for the in and 0.54 singlet molecules bond bisanthene, these the for of calculation, character 0.07 (DFT) diradical be character theory quar-The to diradical functional in larger estimated desnsity a are rings hence, the values six-membered and, character to outer rings According peripheral of bisanthene. the Inaddition, values to at (HOMA) compared character contribution. aromaticity benzenoid diradical more of significant indicates model the teranthene oscillator from harmonic resulting highest Å), (1.447 the bisanthene in one corresponding as alternation thene length bond 50 the nearly about information with further state gave triplet a to activated easily was for singlet signals The NMR of of population of absence lower baseline The the NMR to the singlet attributed contrast, small is In A which SQUID. temperature. lowered low was at temperature species the triplet as observed was sharpening line quarteranthenes desired hydrocarbons the ring-closed partially the afforded fprpnaeewstems pcrsoi eko a-hs ipootoainpout [43]. precursor, products disproportionation potential gas-phase one of only peak spectroscopic and mass reported, the be was Wu peripentacene to by of yet reported graphene-like was is of dicarboximide, types derivative monobromo- these peritetracene for i.e., of expected starting therefore Synthesis anthenes is and state [41]. periacenes ground molecules both open-shell for an phase and onward, antiferromagnetic bisanthene to et from phase Jiang by nonmagnetic conducted from calculations crossover Theoretical methodology. a synthetic out proper of (Fig- lack contribution diradical/polyradical the more and the 16), from ure originating presumably reactivity, high extremely the ( to peritetracene namely been have periacenes, higher-order the or of thesis two like look they because 16), (Figure ( Perylene Periacenes 3.2 15: Figure of Treatment CeCl [40]. of approach presence the synthetic in identical bromides magnesium an using synthesized was teranthene (DDQ)/Sc(OTf) 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone by reaction CeCl of GRUYTER DE – C π 57 bn nryo 6.3ka mol kcal ~64.53 of energy -bond 3 144Å,wihi osdrbysotrta egho C(sp a of length than shorter considerably is which Å), (1.424 olwdb NaI/NaH by followed ytei fKubo of Synthesis 59 − n iatee( bisanthene and ) rpe nrygpfor gap energy triplet ’ eatee( teranthene s 58a/58b 60 2 a esbaeoie saohrcaso PAHs, of class another as subcategorized be can ) PO 58a 58a 2 h CD The . consfrtelrepplto ftemlyacsil rpe species. triplet accessible thermally of population large the for accounts eeae atal ylzdhydrocarbon cyclized partially a generated – n a on ob .8 clmol kcal 0.689 be to found was 1 pntasomto otedrdclfr,bsnhn otisonly contains bisanthene form, diradical the to transformation Upon . )adqatrnhn ( quarteranthene and 1) = 58a 3 eandfa vnwe h eprtr a oee o183K. to was lowered the temperature when even flat remained 2 n usqetrdcieaoaiainwt SnCl with aromatization reductive subsequent and Cl 56a 2 −

ouinof solution ouae rpe pce tr.Tecytlorpi data crystallographic The rt. at species triplet populated % rpe nrygpof gap energy triplet and 56b 61 a n eietcn ( peripentacene and ) pnDDQ/Sc(OTf) Upon . odin bond 57 n ’ ru 4] h nyeprmna evidence experimental only The [42]. group s )derivatives. 2) = – was 1 hc saon he ie esta the than less times three around is which – 2 1 1 58a 3 ) M ieta twieprogressive while rt at silent NMR H π rmSUDwihidctsthat indicates which SQUID from – foddteranthene afforded – bn laaecno eflycom- fully be cannot cleavage -bond C(sp .1ka mol kcal 3.81 s142Å uhsotrta teran- than shorter much Å, 1.412 is peri 2 igebn 147Å n the and Å) (1.467 bond single ) peri fsd epciey h syn- The respectively. -fused, 55 62 3 fsdaee or acenes -fused ,i ut hlegn due challenging quite is ), hc pnring-closure upon which treatment, 54 – 1 ihrsetv aryl- respective with a siae from estimated was 57 a n Wu and Das 3] h quar- The [39]. 56a/56b 2 aei acid /acetic

l pointed al. periacenes gave 58a 9 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd raeigfo 1 o28Kwsatiue otepplto ftetemlyectdtiltseiswhich species triplet excited thermally line the progressive of where population measurement the NMR to VT attributed open-shell was the in K by was sextets 298 derived Clar to was 5 K shell, the 213 closed from from in arising broadening state, sextets ground 2 the to to compared contribution form diradical The [44]. 17) (Figure der tetrabenzo[ the afford to dehydrogenation 63 reagent followed by acidification in air gave the tetraaryl-substituted fused bispentacenequinone the tetraaryl-substituted an air revealed gave analysis in lographic acidification of by treatment followed Further in reagent air. product acidification by addition followed 4-Michael (THF) tetrahydrofuran 1, anhydrous unexpected an instead compound adduct; when 2-addition obtained 1, desired the generate not Wu did by contributed them, of of tion One 19(a)). (Figure succeeded them 18: Figure Clar extra one C only one of form breaking open-shell the the compensate to in enough as high be state not ground may which closed-shell recovered exhibit to [45] reported 17: Figure have of to gap shown energy been has compound the level), B3LYP/6-31G(d,p) 16: Figure 10 by documented approach, synthetic Another reactions. addition Michael et unusual Müllen the for account may which a is rprdi tp n a ujce oGinr ramn olwdb igfusion and oxidative ring bya followed treatment toGrignard wassubjected and 8steps in prepared first was hr r opeo ytei prahstwr eietcn eotdi ieaue;hwvr oeof none however, literatures; in reported peripentacene toward approaches synthetic of couple a are There derivative bistetracene a contrast, In et Müllen by reported recently very was dimer tetracene fused partially A – . clmol kcal 3.4 a n Wu and Das 67 ooti atal ue bis-pentacenequinone fused partially obtain to Briseno Müllen of Synthesis forms. resonance open-shell their and Periacenes

l Fgr 9b) novstecciaino ercaoprn derivative tetracyano of cyclization the involves 19(b)), (Figure al. – . clmol kcal 6.7 ’ ittaeederivative. bistetracene s – 1 drvdfo TER ihrta h ige iaia rudsae hoeial (at Theoretically state. ground diradical singlet the than higher ESR) VT from (derived 68 – ’ iaiaodbistetracene. diradicaloid s 1 a rae ihecs rgadraeto 1-bromo-3,5-di- of reagent Grignard excess with treated was a deduced. was α , β ustrtdktn tutr ntefsdbispentacenequinones fused the in structure ketone -unsaturated 66 a,f,j,o Fgr 8 ihhg-hrecrirmblt f61cm 6.1 of mobility carrier high-charge with 18) (Figure prln absercn nlge derivative analogue) bistetracene (a ]perylene 68 4] oee,tesbeun ulohlcreaction nucleophilic subsequent the However, [46]. ’ ru,ivle h xdtv photocycliza- oxidative the involves group, s y .1,ee huhalresinglet large a though even 0.615, =

l h nemdaecompound intermediate The al. – obebn energy. bond double C 71 oafr h tetraketone the afford to 69 ihecs Grignard excess with tert 65 btlezn in -butylbenzene sgenpow- green as 2 ’ ettwas sextet s V 70 EGRUYTER DE − 68 Crystal- . 1 s – and 69 − triplet 1 was was 69 , Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd iue21: Figure discussed. is system phenalenyl the on based diradicaloids and monoradicals neutral in ef- by dimerization progress synthetic its immediate of suppress deal to modifications great chemical single-component a intermolecular by phenalenyl as stimulated the phenalenyl of use am- stabilization of potential the redox instability for its high forts kinetic claimed and The Haddon molecule, [51]. earlier, entire electroconductors The and the molecular [50]. chemists, over nanographene delocalized of of spin attention properties radical grabbed magnetic the photericity and with electronic phenalenyl intriguing of the structure of planar understanding better a to smallest lead the also is and rings zene ( Phenalenyl PHs Open-Shell Phenalenyl-Based 4 20: Figure shiftof stokes a small and structure absorption UV-vis sharp and fine 20).Thestruc- the (Figure framework cm state by rigid 10 ground reflected The well analysis. is crystallographic X-ray withaclosed-shell compound single-crystal the and core, of spectrum inthe mass by rings established was sextet ture aromatic eight the by defined as a than rather peripentacene DDQ/Sc(OTf) with tion 17 in derivative, pyrene 19: Figure still are bisanthene beyond periacenes that concludes It conducted. were reactions elusive. further no and solubility peripentacenetetraketone the afforded acylation acid-promoted subsequent of cyclodehydrogenation tive 72 GRUYTER DE hc notntl didn unfortunately which erbnoprpnaeederivative tetrabenzo-peripentacene A – 1 . hnlnla noe-hl rpeefamn n t eoac forms. resonance its and fragment graphene open-shell an as Phenalenyl Yamada of Synthesis Müllen. (b) and Wu (a) by reported peripentacene, of synthesis Attempted 77 srgre srigid as regarded is ) σ bn omto swl sratvt oadoye.I h olwn etos h significant the sections, following the In . toward reactivity as well as formation -bond

il yoiainof oxidation by yield % 3 namcoaea 3° 4] hscmon sbte edsrbda tetrabenzo- a as described be better is compound This [49]. 130°C at microwave a in “ ’ peripentacene erbnoprpnaeederivative. tetrabenzo-peripentacene s ’ neg ute htcciain[7.Aotn natraiept yoxida- by path alternative an Adopting [47]. photocyclization further undergo t 71 ntepeec fPIFA/BF of presence the in “ pnselgahn fragment graphene open-shell π cnuae eta aia opsdo raglrfso ftreben- three of fusion triangular a of composed radical neutral -conjugated ” 76 eiaiebcueHM nlssrvae oaie aromaticity localized revealed analysis HOMA because derivative 4]wsrcnl eotdb aaaet Yamada by reported recently was [48] 74 ihFeCl with 3 3 olwn uc eaainadfrhroxida- further and separation quick a following PF:peyidn i(rfuraeae)and bis(trifluoroacetate)) phenyliodine (PIFA: ” Fgr 1.Rsac npeaeyscould phenalenyls on Research 21). (Figure 73 ntaeaon ihvr poor very with amount trace in

l,uiiiganother utilizing al., a n Wu and Das 11 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd f10 of 88 of distance sharp 60 intermolecular of in long formation Å, the the 3.78 by for separated reason columns The in distance. stacked molecule the This to observed. contrast also was stacking nonuniform and propeller-shaped a revealed cation phenalenyl to bene 83 perchloroacenaphthylene material ing et Haddon 22: Figure techniques. first MS the and represented NMR result with this dimer and radical temperatures, lower a at of ionized detection substance allows the which of (MS) weight spectrometry molecular The measurements. NMR the 530 as in crystal) to absorbance Interestingly, (similar of [53]. solution solution bonding in bonding) multicenter purple (pancake of red behavior area dimeric the same opened the eventually showed study that spectroscopic distance short such Waals with der Van well the orates the (2 within of interaction interaction sum exchange antiferromagnetic the strong than intermolecular shorter A antiferromagnetic much atoms. Å, 3.323 the of to of 3.201 formation radius from were the ranging positions showed distance connection interplanar structure the with Crystal motif that in densities. phenalenyl spin parent negligible the of with structure electronic the to turbation the suppress successfully only not substituents the subsequent of of group, reduction by hydroxyl crystals yellow of 4-bromo-2,7-di- pale elimination as on tained reductive Formylation a [52]. by Friedel 22) followed and (Figure reaction hydrolysis 1999 Reformatsky in then air and in lithiation state solid the in three of Introduction Monoradicals Phenalenyl-Based 4.1 12 ovrinof Conversion . xiie ui aaants t100 at paramagnetism Curie exhibited eclrpeaey radical Perchlorophenalenyl – 10 a n Wu and Das 85 cm S ytei fNakasuji of Synthesis afforded

l 5] n h -a rsalgahcsrcue(iue2)wsotie n20 5] h e start- key The [56]. 2001 in obtained was 23) (Figure structure crystallographic X-ray the and [55], al. – 1 tert a esndfrteioaino niiulmlcls making molecules, individual of isolation the for reasoned was 81 85 btlphenalenyl -butyl – 87 o 7 mrgo 5] oedfnt vdnewspoie by low-temperature provided was evidence definite More [54]. region nm 670 86 by rttdsakn oi.Temgei ucpiiiymaueet icoe httesolid the that disclosed measurements susceptibility magnetic The motif. stacking -rotated euto of Reduction . from tert hc newn usqetallrarneeti h rsneo ei cdt yield to acid Lewis of presence the in rearrangement allyl subsequent underwent which – p 82 rfsayain aetepeaaoederivative phenalanone the gave acylation, Crafts clrnli easdtleeafre phenalenyl afforded degassed in -chloranil btlgop tthe at groups -butyl 84 rdal undt leuo oln hc si codnewt h nraeof increase the with accordance in is which cooling upon blue to turned gradually 88 lowsraie ytemlsso ramn ihPPh with treatment or thermolysis by realized was also ’ s tert u oteblyclrn tmidcddfrainfo h lnrstructure, planar the from deformation atom-induced chlorine bulky the to due 88 btlpoetdpeaey monoradical. phenalenyl -butyl-protected ihall with 87 82 foddtearstable air the afforded 85 hc a iei ntesldsaewt uhcoe intermolecular closer much a with state solid the in dimeric was which – a banda itr with mixture as obtained was 8 n niermgei reigblw10K tconductivity rt A K. 100 below ordering antiferromagnetic and K 380 α and - 80 β pstoso hnln epdNksj ihteioainof isolation the with Nakasuji helped phenaleny of -positions σ ihLiAlH with bn ieiain u r lopsesdwt iia per- minimal a with possessed also are but dimerization, -bond β pstossbtttdb hoieao a is rprdby prepared first was atom chlorine by substituted -positions π dmrwsas eetdb odsryinzto mass ionization cold-spray by detected also was -dimer J / 4 88 k n usqetdhdainin dehydration subsequent and B 88 sasiybakhxgnlcytl -a analysis X-ray crystal. hexagonal black shiny a as = a u otennpaaiywihinhibited which non-planarity the to due was – ,0 )fo QI esrmnscorrob- measurements SQUID from K) 2,000 84 80. rmclrnto facenaphthene of chlorination from π 82 dmri ernbn packing herringbone a in -dimer h aia precursor radical The π sde lecytl.Tebulky The crystals. blue deep as 88 dmra vdne yalarge a by evidenced as -dimer tert Mott a 3 btlahhln ( -butylnaphthalene diino dichlorocar- of Addition . – ubr insulator. Hubbard p TO.Oxidation -TsOH. 1 β EGRUYTER DE 81 and H positions a ob- was 78 by ) 13 82 C Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd oamlietrbnigitrcin hc eutdi ml nrydfeec ewe h -andp-modes s- the between difference energy small a in owing p-association, resulted 24). the which (Figure stabilized interaction, adequately bonding structure multicenter planar a its a and whilst radicals to s-dimer, the the of of stack stability 1D the decreased uniform about a of in interaction delocalization electron bonding covalent to led interaction bonding ( bimodal multicenter exhibited utive It molecule. the of stacking equidistant eaieylreXryqaiynelsta t1 hwdtedsiciefauethat feature afforded distinctive liquid the the showed cooling K surprisingly, 10 and, at purple that to yellow needles from quality 230 change X-ray large color at relatively a disappeared by almost accompanied and liquid temperature a to decreasing with intensity The in K. decreased signals ESR The solution. compound to corresponded utcne odn,adtesrnt fatfroantcculn neato a esrdas measured was interaction coupling the antiferromagnetic of strength (2 the and bonding, of multicenter formation (thermodynamically to the rt delocalization from the suppressed extensive intensity of signal also to ESR analysis electron multiline due unchanged unpaired the protection of from evident steric delocalization as dimer extensive sans The state 25). solid (Figure the stabilized) in stable precursor highly of be reduction the by powder black 24: Figure σ ofa σ characterization structural first ofa the radical 2,5,8-tris(pentafluorophenyl)phenalenyl desired the formation the in not DDQ and with dehydrogenation resulted and step 2,8-dibromonaphthalene available final commercially in a from the at steps ten in introduced prepared were that groups pentafluorophenyl 23: Figure GRUYTER DE eete nrdcdt mrv h ouiiyadsaiiy n usqetratoseetal fodda afforded eventually reactions subsequent and stability, and solubility highly the hexa- improve a to to fur- lead and, introduced intermediates to then synthetic supposed were of the was of precursor ring solubility trihydro oxygen-sensitive low benzene very the one the stabilization thermore, but onto the 25), units for (Figure phenalenyl important system monoradical three very delocalized is of delocalization Fusion spin radicals. organic that suggesting of oxygen, with radical phenalenyl the iigeiec o omto fsal oo,d-adtivln pce,making behavior. species, redox tri-valent amphoteric six-stage and with di- compounds mono-, of stable of formation for evidence viding dmrfaue ogsbn .3()Åbtentopeaey ig,teeyipyn h ekeso the of weakness the implying thereby rings, phenalenyl two between Å 1.636(7) s-bond long a featured -dimer od ned ouino the of solution a Indeed, bond. J / i(hnlnlslne hog iemmee igt rdc ooaia system a monoradical toproduce ring five-membered a through linked Bis(phenalenyl)s et Kubo 2014, In π k B dmr h aflf nardtrie tr a lot6 ,wihi ncnrs oterpdrato of reaction rapid the to contrast in is which h, 60 almost was rt at determined air in half-life The -dimer. tert ihnthe within ) σ dmri oi omwsfrhrhae t30Ci easdtb.Tehaigrsle nmelting in resulted heating The tube. degassed a in 300°C at heated further was form solid in -dimer btltiezdcccey derivative-butyl-tribenzodecacyclenyl Kubo Haddon of Synthesis ’ etfurhnlsbtttdpeaey radical. phenalenyl pentafluorphenyl-substituted s n btlsbtttdcompound -butyl-substituted π dmr hc ol pi h OOof SOMO the split would which -dimer,

l re ocet niel1 hi yuiiigtesrn lcrsai neato of interaction electrostatic strong the utilizing by chain 1D ideal an create to tried al. ’ 91 eclrpeaey radical. perchlorophenalenyl s hrfr,compound therefore, ; σ dmri oun tr hwdawl-eovdmliieERsetu that spectrum ESR multiline well-resolved a showed rt at toluene in -dimer – 0 ( K 600 σ dmro neetoial netre hnlnlcmon.The compound. phenalenyl unperturbed electronically an of -dimer σ dmr( -dimer 92 2J 93b 94b ihdcmtyfroee a eotdb uoet Kubo by reported was decamethylferrocene, with / k B niae h omto of formation the indicated hc hwdsxrvril n-lcrnrdxwvs pro- waves, redox one-electron reversible six showed which .Hg hroyai tblt ftepeaey moiety phenalenyl the of stability thermodynamic High ). 90 94a 91 fpnaloohnlsbtttdpeaey radical, phenalenyl pentafluorophenyl-substituted of ) β n t -ie xse sa qiiru itr in mixture equilibrium an as existed s-dimer its and aprdiscaatrzto [59]. characterization its hampered pstoso hnlnl yr precursor hydro A phenalenyl. of -positions σ and 93b π soito oe.I the In modes. association ) nobnigadatbnigMswithin MOs antibonding and bonding into 91 5] h igecytlXryaayi is analysis X-ray single-crystal The [57]. – 0C h -a crystallographic X-ray The 90°C. π dmr ntesldsaewith state solid the in -dimers 94b 91 n fterr examples rare the of one om Dcanwith chain 1D a forms π Tert 93a oe consec- a mode, a n Wu and Das btlgroups -butyl bandas obtained ,

l 5]to [58] al. – ,0 K 1,600 89 was 13 σ - Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd rlsaewssbtnilydsaiie yteeetoi otiuinfo 8 from contribution electronic the by destabilized substantially was state tral et Nakasuji Pentalenodiphenalene Bis(phenalenyl)s 4.2.1 Diradicaloids Phenalenyl-Based 4.2 also was structure [4] having diazaphenalenyl chiral a [64]. effective and radical an stable is [63], as atom radical reported as phenalenyl such stabilize heteroatoms of to incorporation way example, for system; open-shell the stabilize 26: Figure of analogue radical spin-delocalized more a cation prepare the to of dimer attempt reduction mea- the The conductivity however, the performed; [61]. by was insulator demonstrated tetrathiophenalenyl further as was it which revealing contacts pairs, dimer Other surements within SOMOs. trapped of the electrons overlap with of S the isolated as maximizing superposition view, such complete perpendicular lattice, a almost the from in An observed thermodynamically. be radical can atoms neutral carbon the stabilizing atoms sulfur no stituents, this in distance of intermolecular that The than 26). (Figure radicals two between tion phase, crystalline the In species dithiophenalenyl cationic The 26). (Figure sitions et don 25: Figure 14 Modifications within the phenalenyl moiety, instead of around the phenalenyl unit, were also investigated to were also unit, the phenalenyl around of instead moiety, the phenalenyl within Modifications Had- delocalization, extended and hindrance steric less with radicals neutral stable obtain to aim the With a n Wu and Das

101 l eindasre fpeaey aiaswt iufd rdears w egbrn ciepo- active twoneighboring across bridge disulfide a with radicals phenalenyl of series a designed al. ytei n tutrso Haddon of structures and Synthesis Kubo ihaS a with

l Fgr 7 n hwditrsigapoei utsaerdxpoete.Hwvr h neu- the However, properties. redox multistage amphoteric interesting showed and 27) (Figure al. 82 σ dmrzto a omdi h oi tt stesi slreydlclzdee ntetwo the on even delocalized largely is spin the as state solid the in formed was -dimerization ’ niaigasrne nemlclritrcin oal,i pt fteasneo uk sub- bulky of absence the of spite in Notably, interaction. intermolecular stronger a indicating , a i(hnlnl n b rbnoeaylnldrvdsal monoradicals. stable tribenzodecacyclenyl-derived (b) and bis(phenalenyl) (a) s 97 – n tsrie nsldsaei i o pt 4hbtdcmoe ucl nslto [60]. solution in quickly decomposed but h 24 to up for air in state solid in survived it and S σ bn Fgr 6,adol ekERsga a eosre nslto [62]. solution in observed be can signal ESR weak a only and 26), (Figure -bond – 102 neatosbtendifferent between interactions S 98 6] etln uui rdigtopeaey oeis a is eotdby reported first was moieties, phenalenyl two bridging subunit pentalene a [65], tce nasnwc ernbn oi fface-to-face of motif herringbone sandwich a in stacked ’ 98 hnlnl ihdslu bridges. disulfur with phenalenyls s a isl rprdi 98b euto ofthecorresponding byreduction in1978 prepared firstly was π dmr,wr loosre,bttedmr remain dimers the but observed, also were -dimers, 100 π dmr(3.13 -dimer π e ofraino closed-shell a of formation to led eeto nirmtcpentalene antiaromatic -electron π dmr ih10 rota- 180° with -dimers – 3.22 Ǻ see shorter even is ) EGRUYTER DE α Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd hl omwssaiie y84 clmol kcal 8.45 [72]. by stabilized was form shell species dicationic the to assignable stable spectra long week several to compared air of the in decomposed repul- and air-sensitive excited suppressing four-electron extremely to doubly compounds systemby phenalenyl a to of Fusion of led this orbitals. Accommodation occupied ring fully [70]. between stabilized interaction ring state configuration from short thiophene arising substantially sion each ground the with between pairs Å dimeric into 3.1 of mol configuration kinds about kcal two of revealed 1.7 contacts analysis lies crystal nonbonding which single state The ground state. diradical closed-shell glet singlet a predicted level UB3LYP/6-31G(d,p) 27: Figure mol (3.4Å).This kcal atoms carbon glet of than bis(phenalenyl) character naphthalene-linked contact diradical A enhanced der Waals [67]. with covalency van intermolecular the to corresponding orbitals than SOMO molecular the shorter maximize significantly will is mol mode which packing kcal Å, ~4.87 3.137 as of between determined separation tance further energy was the state and rt, triplet of at solid- excited structure species with to triplet together the state temperature accessible lower in singlet thermally at broadening a ground peaks indicated line sharp clearly The of peak emergence [66]. ESR as state 27) well as (Figure temperature solubility elevated the at spectra improve to introduced were substituents IDPL an Afterward, subunit. GRUYTER DE h hnlnlmite,wihcnb oeaeutl ecie smlietrbnig Bis(phenalenyl)s bonding. multicenter ( as on contribution described nature cal adequately spin-localized unit more the anthracene to be by due can linked one which intramolecular moieties, the phenalenyl than stronger the was bonding intermolecular the and h eoeyo diinlaoai igfo unia eoac omt h iaia eoac form. resonance diradical through the to stabilization form aromatic resonance the quinoidal (2) from and ring moiety stabilization aromatic phenalenyl in additional role of major of delocalization play recovery intrinsic factors the two the as (1) state systems: ground diradical the significant singlet of The a observed. by featured was are stack, compounds one-dimensional These a in of molecule contribution a diradical within to compared molecules between in interaction bonding covalent intermolecular in of contribution diradical enhanced 1 105b hohn-ue bis(phenalenyl) thiophene-fused A M inl aen sflifrainabout information useful no gave signals NMR H – rpe a f10 Vand eV 1.04 of gap triplet smr lnae 1473 )cmae ota of that to compared Å) (1.467(3) elongated more is – 1 i(hnlnlsbigdb etln n ifrn rmtclinkers. aromatic different and pentalene by bridged Bis(phenalenyl)s .Tecytlpcigof packing crystal The ). 103d y eosrtdoedmninlcan nsagrdsakn oewt naverage an with mode stacking staggered in chains one-dimensional demonstrated .8 oprdt hi ahhln ( naphthalene their to compared 0.68) = 107a 105 105 a trbtdt h ihaoai tblzto nryo h nhaeebridge. anthracene the of energy stabilization aromatic high the to attributed was and 103a – Fgr 7 eeas eotdb uoet Kubo by reported also were 27) (Figure .7ka mol kcal 3.77 107b 104b ihoebneodrn ue ntecne a eeoe,advarious and developed, was center the in fused ring benzenoid one with 105 106 103 Fgr 8,and 28), (Figure a ute upre ycytlorpi nlssweetebond the where analysis crystallographic by supported further was – dpe iia tpe oeto mode stepped similar adopted OOoelpigbtenterdcl,laigt tblzdinter- stabilized to leading radicals, the between overlapping SOMO – 107b 1 Fgr 8 a eotdt show to reported was 28) (Figure a lorpre 6]t etr mle HOMO smaller a feature to [68] reported also was hntesnltcoe hl,spotn iaia rudstate ground diradical a supporting shell, closed singlet the than – 1 105a 2+ b QI) epciey than respectively, SQUID), (by hrb uprigtefrainof formation the supporting thereby , ihadsac f312Å hc scnieal stronger considerably is which Å, 3.122 of distance a with 107b 107b oee,dsouinof dissolution however, , y 104a .0 n ezn ( benzene and 0.50) = with 1457 )and Å) (1.465(7) tert btlsbttet a eotdt be to reported was substituents -butyl

l 6]adhv vnlre diradi- larger even have and [69] al. 103d y 103d .5adDTcluainat calculation DFT and 0.35 = nteoedmninlchain, one-dimensional the in 103e y 11 Vand eV (1.15 107b .0 oneprs The counterparts. 0.30) = ortho- – 107b 1 1472 ) similar A Å). (1.457(2) 103c h crystallographic The . nD in oiin fphenyl of positions h ige open- singlet The . 7] h absence The [71]. – – 1 a n Wu and Das UOadsin- and LUMO 2 SO eo h sin- the below Δ 4 E S-T aeclear gave 1 π NMR H = – π – 104a 4.37 dis- 15 a Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd eodrnsot h etztrn oe ndfeetmds a edt w smrcsrcue,1,2:9,10- structures, twoisomeric to lead can thermody- the modes, with different together in center core, ben- the heptazethrene two in dibenzoheptazethrene of the fusion ring Vertical onto backbone. linker hydrocarbon rings aromatic entire zenoid on the delocalization of radical through aromaticity stabilization of namic recovery di- the , by ( Unlike bilized heptazethrene 30). of (Figure form resonance respectively radical unit, 2,6-anthraquinodimethane and naphthoquinodimethane, 116 1,2:8,9-dibenzozethrene diphenyl-substituted A state. iue29: Figure unsubstituted for However, 0.128 delocalization. of extended and that to geometry singlet distorted compared large 0.210 the the of to index due probably character most diradical larger 1,2:8,9-dibenzozethrene, exhibits [76], Wu -T. Y. by et Wu by derivative zethrene phenyl-substituted 14-bis(phenylethynyl)zethrene the 7, of investigations experimental could and they synthesis However, therefore, ring, sextet character aromatic diradical et additional open-shell Nakano of remarkable recovery although, state, by ground stabilized closed-shell be show cannot zethrene zethrene called of fragment, form graphene ical Z-shape a generate will moieties 108 phenalenyl two of fusion head-to-head A Zethrenes 4.2.2 28: Figure 16 PH. closed-shell typical a like behave it n nonazethrene and , xeso ftebtdeeui ie ihrodrztrnssc sheptazethrene as such zethrenes higher-order gives unit the of Extension a by fixed are units naphthalene two like looks which , a n Wu and Das

l 7] n aetztrn derivative zethrene parent a and [77], al. ehee iezztrn,adterderivatives. their and dibenzozethrene, Zethrene, spacer. benzene and thiophene with linked Bis(phenalenyl)s

l,bsdo h cuac ubr fsi-netitdHartree spin-unrestricted of numbers occupancy the on based al., – rpe a ( gap triplet 118 117 n 5,6:13,14-dibenzoheptazethrene and ntrpre e)i hc w ahhln nt r rde ya by bridged are units naphthalene two which in yet) reported (not – .2ka mol kcal 7.32 y 110 – 1 .3)adhge ooous(octazethrene, homologues higher and 0.537) = didn ) yY T uet Wu -T. Y. by 108 ’ lo n hral rmtdmgei ciiy making activity, magnetic promoted thermally any allow t yMa et Miao by 114 7] rprdb dpigasmlrapoc used approach similar a adopting by prepared [79], trans

l 7] eheebsabxmd derivative biscarboximide zethrene a [76], al. 13btdeeui Fgr 9 7] h dirad- The [73]. 29) (Figure unit -1,3-butadiene 119

l 7]wr nfvro lsdselground closed-shell a of favor in were [78] al. Fgr 30). (Figure – okntrlobtl UO)[74]. (UNOs) orbitals natural Fock y .0 a rdce by predicted was 0.407 = 109 115 yTb et Tobe by y .2)aesta- are 0.628) = octazethrene , p QM 2,6- -QDM, EGRUYTER DE

l [75], al. 111 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd ebrdrnsrte hnsxmmee ig hc stemdnmclymr aoal.Testructures The favorable. more thermodynamically is which rings of six-membered than rather rings the membered of activation the to attributed with NP derivative observed closed-shell ( was ( character a reaction of species ring cyclization isolation triplet the eventual populated for to leading thermally regio-selectivity to different due a signal that ESR mention broad of HOMO presence mol characteristic low and kcal spectrum with rt absorption configuration at An electronic signal conditions. excited NMR doubly ambient a under of stable admixture and to solvents organic common in ble the BF tune [81]. and derivative 31(b)) stability (Figure the sites improve radical to reactive aim (a the kinetic solubility, extended-heptazethrenebis(dicarboximide) With dimer) the necessary. an monoimide compromising character, was without sites diradical stability radical and the improve reactive bandgap to most order the In characterof state. at solid blocking in theopen-shell or solution as supports ther further state ground the electronic 121 excited doubly the into of associated (H,H-L,L) admixing eV from 0.99 configuration originated of bandgap that electrochemical band low absorption A UV-vis-NIR lower-energy backbone. dis- with hydrocarbon homogeneously entire a the with on state density ground spin diradical diradical tributed singlet singlet of open-shell energy an the supporting respectively, calculations, state, DFT of biradical due basis cooling the upon On state. sharpening singlet line of the progressive state to and equilibrium species the triplet of shift accessible the thermally to of existence the to due rt [80]. intermediate from octadehydronaphthoannulene approach an cyclization of transannular clization a using heptazethrenebis(dicarboximide) by derivative, synthesized was heptazethrene compound stable relatively first the 30: Figure GRUYTER DE 123 hoeia rdcino agrdrdclcaatri etztrn tmltdorgopt synthesize to group our stimulated heptazethrene in character diradical larger a of prediction Theoretical hwdraoal htsaiiyi ouin oee,temtra lwydcmoe uigsoaeei- storage during decomposed slowly material the however, solution; in photostability reasonable showed and 121 – 1 ihrodrztrnsadtodbnoetztrn isomers. dibenzoheptazethrene two and zethrenes Higher-order rmSUD eei ao fissnltdrdclcaatr( character diradical singlet its of favor in were SQUID) from , y 122 125 a oae . n . clmllwrta h lsdselqiodlsaeadoe-hl triplet open-shell and state quinoidal closed-shell the than lower kcal/mol 7.9 and 5.8 located was .0) nta fteetne etztrn eiaie(iue3() 8] hsosrainwas observation This [81]. 31(c)) (Figure derivative heptazethrene extended the of instead 0.009), = olwdb xdtv eyrgnto yDQgv h agtcompound target the gave DDQ by dehydrogenation oxidative by followed r ohcnimdb -a rsalgahcaayi Fgr 31(d)). (Figure analysis crystallographic X-ray by confirmed both are 123 a yteie hc a ieial lce by blocked kinetically was which synthesized was β psto feeto-ihN nt(in unit NP electron-rich of -position 3 ·OEt s idcn-rde eyeedimer perylene -indacene-bridged 2 mdae nrmlclrrn-ylzto ftedimethoxy the of ring-cyclization intramolecular -mediated 1 M pcrmsoe iebodnn at broadening line a showed spectrum NMR H y 124 .6)i rudsae ti ot to worth is It state. ground in 0.465) = ln ihfraino w five- two of formation with along ) – t btlpey rusa h most the at groups phenyl -butyl UOgpo .9e,asneof absence eV, 0.99 of gap LUMO 120 125 novn iutnoscy- simultaneous involving p QMbigdperylene -QDM-bridged ihngiil diradical negligible with 121 Fgr 1a) This 31(a)). (Figure 123 121 a n Wu and Das hc ssolu- is which , Δ Compound . E S-T = – 2.97 124 17 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd a opsto,temlcl ihmr rmtcsxe ig ntedrdclrsnnefrs xiisgetrdiradical greater exhibits forms, resonance diradical the diradicaloids. in rings sextet Hence, aromatic 30). more character. (Figure with ofaromatic forms molecule the resonance number composition, diradical different cal respective the by the explained in was rings structures isomeric sextet two between character diradical in ence ( contribution diradical larger a precursor dihydro a of hydrogenation isomer dibenzoheptazethrene of derivative (a precursor diketone ing 32: Figure covalent average singlet an small with of actions, consequence a Both as SQUID). species on based triplet kcal/mol excited thermally of presence to due of the to similar pattern Compound [82]. tazethrene of tures (c) heptazethrenebis(dicarboximide), extended or dimer 31: Figure 18 127 sn iia ytei taey ulohlcadto fTP-ansu hoiet h correspond- the to chloride TIPS-magnesium of addition nucleophilic strategy, synthetic similar a Using hep- (TIPS)-blocked triisopropylsilylethynyl bulky zethrenes, higher-order the of stability the improve To a n Wu and Das a ute upre ytebroadened the by supported further was 123 π hscnb eadda netnino Clar of extension an as regarded be can This Wu (b) heptazethrenebis(dicarboximide), (a) of structures and Synthesis bnigitrcinse nKubo in seen interaction -bonding and 126 ’ ISbokdhpaeheeadotztrn derivatives. octazethrene and heptazethrene TIPS-blocked s 125 n octazethrene and 119 126 . hc perdt aea pnselsnltdrdclgon tt Fgr 3.Another 33). (Figure state ground diradical singlet open-shell an have to appeared which ) hwdatypical a showed 121 128 π sakn itneo .8ad33 ,rsetvl,wihi agrta intermolecular than larger is which respectively, Å, 3.35 and 3.38 of distance -stacking and olwn euto ihSnCl with reduction following 131 y 123 .7)i h rudsaecmae oisomeric to compared state ground the in 0.576) = 126 127 adrvtv of derivative (a niaigapoal pnselcaatrfor character open-shell probable a indicating and eepeae rmtecrepnigdktn rcros(iue32) (Figure precursors diketone corresponding the from prepared were 130 p bn iia ocoe-hl H,while PHs, closed-shell to similar -band 127 xeietladtertclivsiainrevealed investigation theoretical and Experimental . ’ i(hnlnl-ae diradicaloids. bis(phenalenyl)-based s were packed into a 1D infinite chain via intermolecular chain infinite 1D a into packed were 1 118 M pcrmadteapaac fERsga trt at signal ESR of appearance the and spectrum NMR H s idcn-rde Pdmr d -a rsalgahcstruc- crystallographic X-ray (d) dimer, NP -indacene-bridged ’ a lootie sn D-eitdoiaiede- oxidative DDQ-mediated a using obtained also was ) rmtcsxe uei h ezni Hbsdsinglet PH-based benzenoid the in rule sextet aromatic s 2 rvddadbnoetztrn derivative dibenzoheptazethrene a provided p QMbigdprln monoimide perylene -QDM-bridged ezni H ihtesm chemi- same the with PHs benzenoid 127 127 131 – rpe nrygp( gap energy triplet ipae nabsorption an displayed h pnselnature open-shell The . 039 8] hsdiffer- This [83]. (0.309) 129 EGRUYTER DE π opossess to − π − inter- 3.87 129 Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd ehnceia process. mechanochemical of crystals of All three radicals showed significant stabilities with the half lives of 7, 3.5 and 43daysfor for 134 3.5 solution in 7, dimerization of The lives half the extended delocalization. crystalline through with of theradicals stabilities Compound significant respectively. showed the stability radicals three increases asanthracene densityfrom All center spin fluorenyl theradicals large the with stabilizes [37] of efficiently benzannulation moiety spin centers fluorenyl the the of protect effectively site reactive can most the at group 9-anthryl 34: Figure character diradical moderate a with diradicaloid singlet a as character. regarded tetraradical better minor is and compound singlet this vertical So, large. although quite state, triplet accessible thermally of a of bonds presence short relatively the as analysis length Å), bond crystallographic from alternation length bond strong sharp and clear D et Tobe by prepared successfully hydrocarbon tetraradicaloid potential A PHs Open-Shell Miscellaneous 5 33: Figure GRUYTER DE different models with ( models LC-UBLYP/6-311+G(d,p) where different measured long-range-corrected ( were while a longer characters character much tetraradical Using to radical and shifted conjugation. band diradical absorption extended the energy lowest the method, nm the 475 with of at nm maximum 909 because absorption at wavelengths intense centered an band exhibited broad a It [84]. with together solution in tautomerization valence through tures 2h tbefurnlbsdmnrdcl eercnl eotdb uo(iue3)[5.Teatcmn ofthe attachment [85].The 35) (Figure by Kubo reported recently were monoradicals fluorenyl-based Stable c and tutr,(.0 .6)for 0.166) (1.00, structure, 139Å), (1.349 135 Tobe Wu σ dmr and -dimers i o hwsc S eair oi Vmaueet icoe ehncrmcproperties mechanochromic disclosed measurements UV Solid behavior. ESR such show not did ’ iezhpaeheeisomers. dibenzoheptazethrene s p ’ 133 tetracyclopenta-[ s QMsbnt Notably, subunit. -QDM e 1 133Å and Å) (1.373 M can NMR H 2 and D 135 2h y 134 135 0 , , 2 D y a sltda nuascae ooaia ncytliefr,whereas form, crystalline in monoradical unassociated an as isolated was ’ ( 1 4h xeietlyvldt h pnselgon tt hc locrooae the corroborates also which state ground open-shell the validate experimentally t σ g xse nbt nsoitdmnrdcland monoradical unassociated both in existed 1 )idctdpr errdclcaatr hoeia aclto,o three on calculation, Theoretical character. tetraradical pure indicated 1) (1, = ) dmr)ta niae h iscainof dissociation the indicated that -dimers) def,jkl,pqr,vwx D 139Å,adlne bonds longer and Å), (1.359 ymtyadtecytlsrcue rdce h ( the predicted structure, crystal the and symmetry

4h l,wiho M iecl ail qiirtdbtenistwo its between equilibrated rapidly timescale NMR on which al., 133 tutr n 028 .8)frtecytlorpi tutr.Hwvr a However, structure. crystallographic the for 0.085) (0.258, and structure a vdn rmdces nERsgasa o eprtr,whereas temperature, low at signals ESR in decrease from evident was 1 M inlbodnn t5° a bevdwihwsindicative was which observed was 50°C at broadening signal NMR H 132 ttahnln derivative. ] Fgr 4,tetracyclopenta-[ 34), (Figure b 143Å and Å) (1.433 – rpe nrygpwstertclyfudt be to found theoretically was gap energy triplet σ dmrzto n xgnatc,and attack, oxygen and -dimerization d σ y 140Å od eei ao fthe of favor in were bonds Å) (1.440 def,jkl,pqr,vwx dmrt ooaia ol ea be could monoradical to -dimer 0 , σ y dmrfrsi t oi state. solid its in forms -dimer 1 1 )idctdapr di- pure a indicated 0) (1, = ) y 0 , y 1 ttahnln,was ]tetraphenylene, s(.9,002 for 0.032) (0.095, as ) 133 a n Wu and Das , 134 D and 133 2h a (1.371 struc- gave 135 19 , Automatically generated rough PDF by ProofCheck from River Valley Technologies Ltd 3 a b .Drdcl.Ce e 2013;113:7011 Rev Chem Diradicals. M. Abe (a) [3] applied and fundamentals radicals: Stable in radicals, carbon-centered other and cyclopentadienyls, Phenalenyls, editors. S. YT, Nishida Wu Y, JS, Morita Siegel [2] chemistry. current in topics I: Polyarenes in nanographenes, 2D open-shell and Closed-shell J. Wu Z, Sun [1] References Osaka in contributions. valuable Nakano 978-3-11-028450-8. their Masayoshi for T. Professor University K. Technological University, J. Nanyang Professor Niigata in Professor Singapore, Webster in of and D. Furukawa University R. Casado National Professor K. J. and in University, Professor thanks Ding KAUST, Professor University, special J. in Yonsei Professor say Huang in Malaga, to -W. Tier3 of Kim like University grants (MOE2014-T2-1-080), D. would in Navarrete 2 Professor also Lopéz Tier We collaborators, MOE (1431AFG100). major grant other by AcRF JCO to A*STAR supported and financially (MOE2014-T3-1-004) was grant Singapore at project The Acknowledgments [86], Lambert by said As Conclusion 6 35: Figure 20 nonlinear for molecules of class new a to applications molecules: singlet open-shell of properties and energies Excitation M. Nakano [4] level. molecular the in systems such pathforthe of make issues evolveto stabilization approaches the synthetic on realistic believed understanding that is given clear [93] a materials Such advancement from spintronic [92]. next-generation the as aselectroconductor [90], PHs inves- batteries and open-shell Furthermore, molecule-based andlately, [89]. in 88] [91], reported promise [4, showed transistors been fragments field-effect also graphene have process open-shell material singlet-fission molecular-sized [3]e]. Theirrole device of of ours emitting terms tigations light in including organic investigated for groups been results several justi- also promising withmoderate by was had systems devices which was observed) photovoltaic Open-shell 87] future sciences. section [4, in TPAcross properties inmaterials NLO (large experimentally third-order their importance fied impressive showed theoretically, torealize contribution, bemade diradical to have efforts eeorns ytei,poete,adapiain.Jh ie osIc.()2015:1 (h) Inc.. Sons & Wiley John applications. and properties, synthesis, heteroarenes: 2015;44:111 Lett. Chem 2015;15:218 Rec. Res.47:2582 Chem Chem hydrocarbons. Acc aromatic state. polycyclic ground biradical singlet a with 2013;8:2894 periacenes J. and Asian p-QDMs, Chem state. ground biradical open-shell an with 2012;41:7857 Rev. Soc Chem radicals. open-shell to semiconductors and 2012;22:4151 2015:1 Chem. and Inc., properties, Sons synthesis, & heteroarenes: Wiley and John editor. arenes Polycyclic M, in: Qian hydrocarbons, applications. polycyclic benzenoid Open-shell J. Wu S, Das (h) 122. 2015;15:218 47:2582 Rec 2014; Chem Res drocarbons. Chem Acc state. ground biradical singlet a with 2013;8:2894 J Asian Chem state. ground biradical open-shell 2012;41:7857 Rev Soc Chem radicals. open-shell to conductors 2012;22:4151 2010:81 Germany, editor. RG, Hicks compounds. odd-electron of aspects 2014:197 Heidelberg, Springer-Verlag Berlin isbn (2016), Gruyter De Nanostructures. Carbon of Chemistry Feng, Muellen, in: available also is article This pisadsnltfiso,Srne nentoa ulsig 04 O:10.1007/978 DOI: 2014. Publishing, International Springer fission, singlet and optics a n Wu and Das Kubo – 0 c u ,Y ,CiC uJ o ada oyylchdoabn:fo lsdselna nrrdde n semi- and dyes infrared near closed-shell from hydrocarbons: polycyclic bandgap Low J. Wu C, Chi Q, Ye Z, Sun (c) 60. ’ xeddfurnlmonoradicals. fluorenyl extended s – 10()[]SnZ eQ h ,W .Lwbngpplcci yrcros rmcoe-hl erifae dyes infrared near closed-shell from hydrocarbons: polycyclic bandgap Low J. Wu C, Chi Q, Ye Z, Sun (b).[3] 4160 – 2 g.3 a ,W .Oe-hl ezni oyylchdoabn.I:Qa ,eio() oyylcaee and arenes Polycyclic editor(s). M, Qian In: hydrocarbons. polycyclic benzenoid Open-shell J. Wu S, Das (g).[3] 122 “ h uueo hs iaia Asceryle nmtrasscience materials in lies clearly PAHs biradical these of future the – 2 g uoT eetpors nqiodlsnltbrdclmlcls hmLt 2015;44:111 Lett Chem molecules. biradical singlet quinoidal in progress Recent T. Kubo (g) 32. – – 248. 8 b u ,W .Oe-hl oyylcaoai yrcros ae Chem Mater J hydrocarbons. aromatic polycyclic Open-shell J. Wu Z, Sun (b) 88. – 3 f.3 uoT eetpors nqiodlsnltbrdclmolecules. biradical singlet quinoidal in progress Recent T. Kubo (f).[3] 232 – 6[]SnZ uJ pnselplcci rmtchdoabn.JMater J hydrocarbons. aromatic polycyclic Open-shell J. Wu Z, Sun 36.[3] – – 0.()SnZ egZ uJ ehee,extended Zethrenes, J. Wu Z, Zeng Z, Sun (e) 904. 9 d u ,Zn ,W .Bneodplcci yrcroswt an with hydrocarbons polycyclic Benzenoid J. Wu Z, Zeng Z, Sun (d) 89. – 1 f uoT hnlnlbsdoe-hl oyylcaoai hy- aromatic polycyclic open-shell Phenalenyl-based T. Kubo (f) 91. – – 89()[]SnZ egZ uJ ezni oyylchydro- polycyclic Benzenoid J. Wu Z, Zeng Z, Sun (c).[3] 7889 145. – 94()[]SnZ egZ uJ ehee,extended Zethrenes, J. Wu Z, Zeng Z, Sun (d).[3] 2904 – – 3 51()[]Kb .Peaey-ae open-shell Phenalenyl-based T. 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