The Structural Origins of Intense Circular Dichroism in a Waggling Helicene Nanoribbon Nathaniel J

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The Structural Origins of Intense Circular Dichroism in a Waggling Helicene Nanoribbon Nathaniel J. Schuster,* Leo A. Joyce, Daniel W. Paley, Fay Ng, Michael L. Steigerwald,* and Colin Nuckolls*

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ABSTRACT: We report the synthesis of a new perylene-diimide- based helical nanoribbon, which exhibits the largest molar electronic circular dichroism in the visible range of any molecule. This nanoribbon also displays a substantial increase in molar circular dichroism relative to a smaller helical analogue, even though they share a similar structure: both nanoribbons incorporate two conformationally dynamic double-[4]helicene termini and a rigid [6]helicene-based core within their helical superstructures. Using DFT and TDDFT calculations, we find that the double-[4]helicenes within both nanoribbons orient similarly in solution; as such, conformational differences do not account for the disparities in circular dichroism. Instead, our results implicate the configuration of the double-[6]helicene within the larger nanoribbon as the source of the observed chiroptical amplification.

■ INTRODUCTION absorbance into the visible range,12 but the manner of fusion This article concerns a new chiral nanoribbon, whose dictates the overall sensitivity to circularly polarized light. For enormous circular dichroism originates from the configuration instance, two helicenes of like handedness can be connected to give chiral isomers of X- or S-configuration (Figure 1),13 but of the double-helicene at its core. As intrinsically chiral ff semiconducting chromophores, helicenes1helices of fused the e ect on ECD varies: for simple carbohelicenes, these double-helicenes can more than double ECD relative to their aromatic subunits surrounding a nonintersecting stereogenic 10 fi axis (e.g., carbo[5]helicene in Figure 1)are potentially monomers; however, these same con gurations for heterohelicenes have elicited comparatively modest ECD.14 Fur- excellent building blocks of chiral electronics and optoelec- 2 thermore, the integration of more than two helicenes into a tronics. This potential utility arises, in part, from their single nanographene rarely enhances ECD;15 in fact, many Downloaded via COLUMBIA UNIV on July 24, 2020 at 20:28:09 (UTC). structural adaptability: one helicene may incorporate a large π- 3 4 multihelicene nanographenes have similarly intense (or surface, a wide diameter, and/or diverse chemical function- 5 smaller) molar ECD (Δε) relative to that of just one of their ality. Such structural variation can be used to promote 16 6 helicene subcomponents. Therefore, a general molecular chiroptical tuning in response to different stimuli, to enable

See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. architecture that incorporates multiple helicenes for the supramolecular self-assembly into chiral aggregates with 7 purpose of consistently enhancing ECD and its dissymmetry enhanced nonlinear optical properties, to detect chiral small (|Δε|/ε) in the visible range remains unidentified. molecules,8 or to spin-filter electrons.9 In brief, helicenes are Here, we present a double-[6]helicene nanoribbon, WH- versatile building blocks of chiral materials for electronics, [6][6] (Figures 1 and 2), that exhibits the largest ECD in the optoelectronics, and other technologies. visible range of any molecule. Three key structural elements Semiconductors for chiral optoelectronics should strongly constitute this nanoribbon: (1) five perylene-3,4,9,10-tetracar- and preferentially interact with one hand of chiral light (e.g., boxylic-diimide (PDI) subunits, which absorb visible light circularly polarized light) across a wide range of wavelengths. intensely; (2) two conformationally labile double-[4]helicenes, Most helicenes do not fulfill these criteria: their absorbance is whose rapid waggling in solution mitigates intermolecular π-to- largely restricted to the ultraviolet regime, and methods to enhance their absorbance of just one hand of chiral light have only begun to be explored.10 For example, the quintessential Received: January 17, 2020 carbo[n]helicene framework (n denotes the number of ortho- Published: April 3, 2020 fused benzene rings) just begins to absorb visible light at n =7, and further elongation (n = 8, 9, etc.) elicits no significant increases in electronic circular dichroism (ECD).11 The fusion of multiple helicenes into a single nanographene can extend

Figure 2. Chiral nanoribbons WH[6][6] and WH[6] share a similar structure−two conformationally dynamic double-[4]helicenes (or- ange) linked by a rigid [6]helicene-based core (blue)−but diﬀer markedly in the intensity of their ECD.

respectively. Subsequent 2-fold visible-light-induced oxidative cyclization provided racemic WH[6] and WH[6][6]. These routes parallel our previously reported syntheses of the PDI- helicenes NPDH and NP3H (Scheme 1),19 which constitute the centers of WH[6] and WH[6][6], respectively. Extensive intramolecular π-to-π overlap within the NPDH and NP3H fragments locks the global chirality of WH[6] and WH[6][6] Figure 1. Two helicenes of like handedness can be fused to give X, S, fi and also precludes the formation of meso-WH[6][6] (i.e., the or M con gurational isomers, as illustrated here with two left-handed isomer incorporating [6]helicenes of opposite handedness); carbo[5]helicenes. These configurations impart chirality and, in turn, chiroptical properties to many nanoribbons. In WH[6][6], the thus, preparative chiral high-performance liquid chromatog- double-[6]helicene M-configuration elicits extraordinarily intense raphy at room temperature resolved the left- and right-handed ECD throughout the UV−visible range. isomers of WH[6] and WH[6][6] (Figure S1), whose ECD spectra (Figure 3a) confirmed their optical purity and reflected the anticipated stereochemical relationship. π aggregation; and (3) a double-[6]helicene, whose left- or The ECD spectra of WH[6][6] and WH[6] share similar right-handed M-configuration (Figure 1) dictates the global profiles but differ substantially in intensity (Figure 3a): most |Δε| −1 −1 chirality of the nanoribbon. We attribute the intense ECD of notably, WH[6] has a max of 350 M cm at 419 nm, fi |Δε| WH[6][6] primarily to this double-[6]helicene M-con gu- whereas WH[6][6] has an extraordinarily large max of 1760 ration: WH[6], the mono-[6]helicene analogue of WH[6][6] M−1 cm−1 at 420 nm (a 5-fold increase). This |Δε| of (Figure 2), exhibits much smaller |Δε| and |Δε|/ε throughout WH[6][6] is the largest ECD in the visible range of any the UV−visible range. In contrast, WH[6][6] and WH[6] discrete molecule.15a,20 More generally, for nearly every Cotton exhibit near-identical absorbance of unpolarized UV−visible effect of WH[6], WH[6][6] displays an isoenergetic and sign- light. Conformational factors do not account for the differences matched Cotton effect, but of much greater intensity. For in |Δε| between WH[6][6] and WH[6]:theirdouble- example, the longest wavelength bands of WH[6] and [4]helicenes orient similarly in solution. Instead, our results WH[6][6] have a |Δε| of 78 M−1 cm−1 at 572 nm and 496 implicate the double-[6]helicene M-configuration as the M−1 cm−1 at 573 nm, respectively. These increases in ECD structural unit responsible for the amplification of ECD. cannot be attributed to differences between WH[6][6] and WH[6] in the absorbance of unpolarized light: their UV− ■ RESULTS AND DISCUSSION visible absorbance spectra (and their fluorescence) are very The designs and syntheses of WH[6][6] and WH[6] evolved similar in profile and intensity (Figures 3b and S2); notably, from those of previously reported PDI-based nanoribbons WH[6] and WH[6][6] exhibit the same ε at ∼420 nm, the (Scheme 1).17 In particular, the direct bromination of the wavelength corresponding to their largest (but immensely ff double-[4]helicene hPDI2 gives 1, which has enabled the di erent) ECD. Therefore, WH[6][6] substantially increases preparation of several aryl frameworks.18 In this case, the both |Δε| and its dissymmetry (|Δε|/ε, Figure 3c) relative to Suzuki-Miyaura cross-coupling of two equivalents of 1 with the WH[6] throughout the UV−visible range. Moreover, |Δε| and diborylated species 2 or 3 (see the Supporting Information for |Δε|/ε of WH[6][6] exceed those of multihelicene X-like fi |Δε| details concerning their preparation) yielded 4 or 5, frameworks that also incorporate ve PDI subunits ( max of

7067 https://dx.doi.org/10.1021/jacs.0c00646 J. Am. Chem. Soc. 2020, 142, 7066−7074 Journal of the American Chemical Society pubs.acs.org/JACS Article

a Scheme 1. Syntheses of WH[6] and WH[6][6] from the Double-[4]Helicene hPDI2 (R = CH(C5H11)2)

aSee the Supporting Information for additional information regarding these syntheses.

≤ −1 −1 |Δε| ε −3 16g,h 300 M cm and / of 10 ) thus incorporating The hPDI2 subunits within WH[6] and WH[6][6] also more PDI subunits into a chiral nanographene alone does not waggle freely, so both nanoribbons assume many conforma- dramatically amplify ECD. tions in solution. Fortunately, WH[6] and WH[6][6] also We suspected that differences in molecular structure (other share the same fundamental structure, which simplified our than the number of PDI subunits) would account for the conformational analysis and the determination of the structural disparities in |Δε| between WH[6][6] and WH[6]. Structur- origins of their ECD. Namely, the rigid [6]helicene-based ally, the double-[6]helicene M-configuration distinguishes cores of WH[6] and WH[6][6] dictate global chirality, WH[6][6] from WH[6] and has been implicated in the whereas their hPDI subunits, each with two symmetrically fi 19 2 dramatic ampli cation of ECD from NPDH to NP3H. But inequivalent [4]helicenes, waggle between four orientations: t- 21 molecular conformation can also profoundly impact ECD, MM, t-PP, t-PM, and t-MP (Figure 5a). As such, the globally π and whereas the -surfaces of NPDH and NP3H are left- or right-handed π-surface of both WH[6] and WH[6][6] essentially locked, those of WH[6] and WH[6][6] change rapidly interconverts between ten conformations in solution considerably at room temperature (vide infra). Thus, (Figures S3 and S4); however, only three conformations pinpointing the double-[6]helicene as the structural unit exclusively incorporate energetically favored MM and/or PP. most critical in amplifying ECD necessitates an analysis of DFT calculations of the ten geometrically optimized left- the conformational isomerism of WH[6][6] and WH[6]. fi π handed isomers of WH[6] identi ed these three as the most The -conformations of WH[6][6] and WH[6] originate stable conformations (Figure 5c): MM-M[6]-MM,MM-M[6]- from the orientations of the [4]helicenes within their two PP, and PP-M[6]-PP (Figure 5b). Together, they constitute hPDI subunits; as such, an understanding of the energies and 2 effectively 100% of the solution ensemble at room temperature, dynamics of the conformations of hPDI enables the 2 which predisposes crystallization of WH[6] as one (or a determination of the predominant stereoisomers of WH[6][6] ff π mixture) of the three; indeed, single-crystal X-ray di raction and WH[6]. The -surface of hPDI2 adopts three forms (Figure 4): helical MM (i.e., two left-handed [4]helicenes), (SCXRD) revealed that racemic WH[6] assembles from a which flattens the PDI subunits at the expense of twisting the room temperature solution into an achiral cruciform lattice of PP PP-M[6]-PP and its enantiomer, MM-P[6]-MM (Figure 6). ethylene bridge; its enantiomer (i.e., two right-handed π [4]helicenes); and meso PM, which distorts the PDI subunits The remaining seven -conformations of WH[6] can be gathered into two higher energy tiers: the four with a single t- into shallow bowls. The geometric optimization of these MP PM stereoisomers by density functional theory (DFT) at the or t- subunit (Tier 2 in Figure 5c) and the three with MP PM B3LYP/6-31G** level revealed the helical isomers to be more either t- or t- subunits or both (Tier 3). The most PM Δ stable conformations within these two tiers have energies stable than ( G298 K = 5.4 kcal/mol); put simply, the (ΔG ) of 5.6 and 10.6 kcal/mol, which essentially match ethylene bridge of hPDI2 distorts from planarity more easily 298 K than the PDI subunits it links. The inversion of one the penalty of converting helical hPDI2 to its meso form [4]helicene in MM or PP provides PM, and the subsequent (Figure 5c). Thus, the energies (and relative amounts) of the inversion of the other [4]helicene completes the enantiome- conformations of WH[6] arise fundamentally from the rization. We identified the helical-to-meso inversion transition orientations of the [4]helicenes within hPDI2. The same state, which has a modest attendant barrier (ΔG‡ ) of 10.9 should be true for WH[6][6]: its PDI termini also waggle 298 K π kcal/mol; thus, hPDI2 overwhelmingly manifests (>99%) in without steric interference by the rest of its -surface. solution at room temperature as an ensemble of helical Therefore, MM-M[6][6]-MM, MM-M[6][6]-PP, and PP- conformations (MM and PP) that rapidly waggle through their M[6][6]-PP (Figure 5d) and their enantiomers overwhelm- meso intermediate (PM). ingly predominate in solution at room temperature.

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WH[6][6] can be more precisely assessed by time-dependent (TD) DFT calculations. Specifically, we calculated the 100 lowest-energy singlet excited states (CAM-B3LYP/6-31+ +G**) of each of the three most stable left-handed conformations of WH[6] (i.e., MM-M[6]-MM, MM-M[6]- PP, and PP-M[6]-PP) and WH[6][6] (i.e., MM-M[6][6]- MM, MM-M[6][6]-PP, and PP-M[6][6]-PP) and generated their corresponding UV−visible absorbance and ECD spectra at the purely electronic level.22 Our calculations reveal that these conformations of WH[6] would be nearly indistinguish- able by UV−visible absorbance (Figure S5a). The three most stable conformations of WH[6][6] also exhibit essentially identical UV−visible absorbance (Figure S5b). In contrast, the predicted ECD spectra of MM-M[6]-MM, MM-M[6]-PP, and PP-M[6]-PP differ in sign and intensity, as do the predicted ECD spectra of MM-M[6][6]-MM, MM-M[6][6]-PP, and PP-M[6][6]-PP (Figure 7). For WH[6], the calculated ECD of MM-M[6]-MM reproduces the experimental spectrum, with a slight energy offset between corresponding bands below 350 nm (Figure 7a). The calculated spectrum of MM-M[6]-PP does not match the bands in sign above 450 nm, and the spectrum of PP-M[6]-PP poorly fits the experimental data; thus, the ECD of left-handed WH[6] originates principally from MM-M[6]-MM. Steric effects may favor the dominance of MM-M[6]-MM in the solution ensemble: it mitigates tail-to- tail collisions between its PDI termini better than MM-M[6]- PP and PP-M[6]-PP.AsforWH[6][6], the ECD of MM- M[6][6]-MM best aligns with the experimental spectrum, particularly in sign and intensity above 450 nm (Figure 7b). In short, our TDDFT calculations indicate that the ECD of WH[6] and WH[6][6] originates principally from the conformations whose [4]helicenes orient with the handedness of the global helix: MM-M[6]-MM and its enantiomer for WH[6] and MM-M[6][6]-MM and its enantiomer for WH[6][6]. Conformational differences do not account for the disparities in |Δε| and |Δε|/ε between WH[6] and WH[6][6]: the [4]helicenes within their hPDI2 subunits orient similarly in Figure 3. (a) ECD, (b) UV−visible absorbance, and (c) dissymmetry solution, and the ECD spectra predicted for the resultant factor of WH[6] and WH[6][6] in dichloromethane (10−6 M, 1 cm conformations (MM-M[6]-MM and MM-M[6][6]-MM) path length) at room temperature. largely reproduce the increase in |Δε| from WH[6] to WH[6][6] (Figure S6). Moreover, our TDDFT calculations Having established that WH[6] and WH[6][6] over- indicate that the signs of the largest ECD in both WH[6] and whelmingly assume three conformations apiece in solution, WH[6][6] (i.e., the bisignate bands from 380−430 nm in we next determined the contributions of these conformations Figure 3a) do not change with conformation: for this to the observed ECD. The relative abundance of the dominant wavelength regime, all of the left-handed conformations exhibit conformations of WH[6] and WH[6][6] does not exactly a negative-to-positive couplet with decreasing wavelength reflect the energies calculated from their DFT models: these (Figure 7), whereas the right-handed conformations exhibit a models use methyl groups in lieu of the 6-undecyl imide tails. positive-to-negative couplet. Besides enabling the assignment Instead, the conformational compositions of WH[6] and of absolute chirality for WH[6] and WH[6][6],the

Figure 4. In solution at room temperature, hPDI2 rapidly isomerizes between its helical (MM and PP) and meso (PM) forms via inversion of its Δ ** [4]helicene subcomponents. All energies correspond to G298 K calculated at the B3LYP/6-31G level of DFT.

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Figure 5. (a) The hPDI2 termini of WH[6] and WH[6][6] waggle between four orientations: t-MM, t-PP, t-PM, and t-MP. This waggling gives ten left- or right-handed π-conformations of WH[6] (we used the left-handed geometries in our calculations). Three of these ten contain, Δ ** exclusively, energetically favored helical-hPDI2 subunits (b). (c) The energies ( G298 K) of the ten conformations (B3LYP/6-31G ) scale with ff the number of meso-hPDI2 (i.e., PM) subunits incorporated, so MM-M[6]-MM, MM-M[6]-PP, and PP-M[6]-PP constitute e ectively 100% of the solution ensemble of left-handed WH[6]. Similarly, MM-M[6][6]-MM, MM-M[6][6]-PP, and PP-M[6][6]-PP dominate the conformational ensemble of left-handed WH[6][6] (d). ■ CONCLUSION We have reported a new chiral nanoribbon, WH[6][6], which exhibits the largest ECD in the visible range of any molecule. WH[6][6] shares a fundamental structure with its smaller analogue, WH[6]: two conformationally labile double-[4]- helicenes linked to a rigid [6]helicene-based core. Never- theless, WH[6][6] displays a tremendous increase in ECD intensity relative to WH[6] across the UV−visible range. For |Δε| −1 −1 example, WH[6] has a max of 350 M cm at 419 nm, |Δε| −1 −1 whereas WH[6][6] has a max of 1760 M cm at 420 nm. These enhancements in ECD cannot be attributed to differences in the absorbance of unpolarized light by WH[6] and WH[6][6]: their UV−visible absorbance spectra nearly match in profile and intensity. Moreover, the disparities in the intensity of their ECD do not stem from conformational differences: the double-[4]helicenes within WH[6] and WH[6][6] orient similarly in solution. Instead, the insensitivity of the largest ECD bands in WH[6][6] (i.e., the bands from Figure 6. From SCXRD, the solid-state structure of racemic WH[6], 380−430 nm) to conformational change indicates they which packs as the PP-M[6]-PP conformation and its enantiomer originate from a rigid chiral substructure: the double- (black and gray carbon atoms, respectively). Hydrogen atoms and the [6]helicene M-configuration at the core of the nanoribbon. undecyl imide tails have been hidden to provide an unobstructed view Few double-helicene M-configurations, naked or incorporated of the π-surface. The PDI termini of left- and right-handed WH[6] π into a chiral nanoribbon, such as WH[6][6], have been slip-stack to give an achiral chain (a), whose -surface orients 23 orthogonally to the π-surfaces of adjacent chains (b). reported, and only the ECD of PDI-based systems have been disclosed.19 Therefore, we are currently investigating the underlying electronic structures of the PDI-based double- permanence of this ECD couplet across all conformations helicene M-configurations to provide a qualitative under- implies an origin in a rigid chiral substructure: fundamentally, standing of the origins of their intense ECD. This under- the [6]helicene core of WH[6] and the double-[6]helicene M- standing can then inform the design of other helicene-based configuration of WH[6][6]. Therefore, our results implicate nanoribbons with extraordinary chiroptical properties. These the double-[6]helicene M-configuration as the structural new molecules will be outstanding chiral and chiroptical component responsible for the dramatic amplification of ECD. material candidates for electronics and optoelectronics.

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Authors Leo A. Joyce − Department of Process Research and Development, Merck and Co., Inc., Rahway, New Jersey 07065, United States; orcid.org/0000-0002-8649-4894 Daniel W. Paley − Columbia Nano Initiative, Columbia University, New York, New York 10027, United States Fay Ng − Department of Chemistry, Columbia University, New York, New York 10027, United States Complete contact information is available at: https://pubs.acs.org/10.1021/jacs.0c00646

Author Contributions All authors have given approval to the final version of the manuscript. Funding U.S. Office of Naval Research Award No. N00014−16−1− 2921, Department of Energy Award No. DE-SC0019440, National Institutes of Health Award No. S10OD025102. Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS C.N. thanks Sheldon and Dorothea Buckler for their generous support. Support for this research was provided by the U.S. Office of Naval Research under award No. N00014-16-1-2921. Synthesis was performed by N.J.S. under support by the U.S. Department of Energy (DOE) under award no. DE- SC0019440. L.A.J. acknowledges Edward C. Sherer for helpful discussions and his assistance in setting up the ECD calculations. The ECD spectra were recorded at the Precision ** Biomolecular Characterization Facility (PBCF) at Columbia Figure 7. TDDFT-predicted (CAM-B3LYP/6-31++G )ECD University. Essential instrumentation in the PBCF was made spectra of the most stable left-handed conformations of WH[6] (a) and WH[6][6] (b) overlaid on the experimental ECD of optically possible by funding from the U.S. National Institutes of Health pure WH[6] and WH[6][6] in dichloromethane (10−6 M, 1 cm path under award no. S10OD025102. We thank Jia Ma for his length) at room temperature. Details concerning these calculations management of the PBCF. SCXRD was performed at the and the spectral fitting can be found in the Supporting Information. Shared Materials Characterization Laboratory (SMCL) at Columbia University. Use of the SMCL was made possible by ■ ASSOCIATED CONTENT funding from Columbia University. N.J.S. thanks Brandon Fowler for helpful discussions concerning mass spectrometry. *sı Supporting Information The Supporting Information is available free of charge at ■ REFERENCES https://pubs.acs.org/doi/10.1021/jacs.0c00646. fi (1) (a) Shen, Y.; Chen, C.-F. Helicenes: Synthesis and Applications. Additional gures, general experimental information, Chem. Rev. 2012, 112, 1463−1535. (b) Gingras, M. One hundred synthetic procedures and characterization data, NMR years of helicene chemistry. Part 1: non-stereoselective syntheses of spectra, DFT-calculated structures and thermochemical carbohelicenes. Chem. Soc. Rev. 2013, 42, 968−1006. (c) Gingras, M.; properties, TDDFT-calculated spectra and excited state Felix,́ G.; Peresutti, R. One hundred years of helicene chemistry. Part data, Beer−Lambert plots, and SCXRD data (PDF) 2: stereoselective syntheses and chiral separations of carbohelicenes. checkCIF/PLATON report (PDF) Chem. Soc. Rev. 2013, 42, 1007−1050. (d) Gingras, M. One hundred Structure of WH[6] from SCXRD (CIF) years of helicene chemistry. Part 3: applications and properties of carbohelicenes. Chem. Soc. Rev. 2013, 42, 1051−1095. (2) (a) Brandt, J. R.; Salerno, F.; Fuchter, M. J. The added value of ■ AUTHOR INFORMATION small-molecule chirality in technological applications. Nat. Rev. Chem. Corresponding Authors 2017, 1, 45. (b) Pop, F.; Zigon, N.; Avarvari, N. Main-Group-Based Nathaniel J. Schuster − Department of Chemistry, Columbia Electro- and Photoactive Chiral Materials. Chem. Rev. 2019, 119, University, New York, New York 10027, United States; 8435−8478. Email: [email protected] (3) (a) Mori, K.; Murase, T.; Fujita, M. One-Step Synthesis of − Department of Chemistry, Columbia [16]Helicene. Angew. Chem., Int. Ed. 2015, 54, 6847−6851. Michael L. Steigerwald ́̌ ̌̌ ̌̌ ́ University, New York, New York 10027, United States; (b) Buchta, M.; Rybacek, J.; Jancarík, A.; Kudale, A. A.; Budesínsky, M.; Chocholousovǎ ,́ J. V.; Vacek, J.; Bednarová ,́ L.; Císarovǎ ,́ I.; Email: [email protected] ́ ́ − Department of Chemistry, Columbia Bodwell, G. J.; Stary, I.; Stara, I. G. Chimerical Pyrene-Based Colin Nuckolls [7]Helicenes as Twisted Polycondensed Aromatics. Chem. - Eur. J. University, New York, New York 10027, United States; 2015, 21, 8910−8917. (c) Schuster, N. J.; Paley, D. W.; Jockusch, S.; orcid.org/0000-0002-0384-5493; Email: cn37@ Ng, F.; Steigerwald, M. L.; Nuckolls, C. Electron Delocalization in columbia.edu Perylene Diimide Helicenes. Angew. Chem., Int. Ed. 2016, 55, 13519−

7071 https://dx.doi.org/10.1021/jacs.0c00646 J. Am. Chem. Soc. 2020, 142, 7066−7074 Journal of the American Chemical Society pubs.acs.org/JACS Article

13523. (d) Fujikawa, T.; Preda, D. V.; Segawa, Y.; Itami, K.; Scott, L. Enantioenriched Helicenes and Helicenoids Containing Main-Group T. Corannulene−Helicene Hybrids: Chiral π-Systems Comprising Elements (B, Si, N, P). Chem. Rev. 2019, 119, 8846−8953. Both Bowl and Helical Motifs. Org. Lett. 2016, 18, 3992−3995. (6) Isla, H.; Crassous, J. Helicene-based chiroptical switches. C. R. ̌ (e) Nejedly,́ J.; Samal,́ M.; Rybaćek,̌ J.; Tobrmanova,́ M.; Szydlo, F.; Chim. 2016, 19,39−49. Coudret, C.; Neumeier, M.; Vacek, J.; Vacek Chocholousovǎ ,́ J.; (7) Verbiest, T.; Elshocht, S. V.; Kauranen, M.; Hellemans, L.; ̌ Budešínsky̌ ,́ M.; Saman, D.; Bednarová ,́ L.; Sieger, L.; Stara,́ I. G.; Snauwaert, J.; Nuckolls, C.; Katz, T. J.; Persoons, A. Strong Stary,́ I. Synthesis of Long Oxahelicenes by Polycyclization in a Flow enhancement of nonlinear optical properties through supramolecular Reactor. Angew. Chem., Int. Ed. 2017, 56, 5839−5843. (f) Marquez,́ I. chirality. Science 1998, 282, 913−915. ̃ (8) Kalachyova, Y.; Guselnikova, O.; Elashnikov, R.; Panov, I.; R.; Fuentes, N.; Cruz, C. M.; Puente-Munoz, V.; Sotorrios, L.; ̌ ̌ Marcos, M. L.; Choquesillo-Lazarte, D.; Biel, B.; Crovetto, L.; Gomez-́ Zadný ,́ J.; Církva, V.; Storch, J.; Sykora, J.; Zaruba, K.; Svorcík,̌ V.; Bengoa, E.; Gonzalez,́ M. T.; Martin, R.; Cuerva, J. M.; Campaña, A. Lyutakov, O. Helicene-SPP-Based Chiral Plasmonic Hybrid Structure: G. Versatile synthesis and enlargement of functionalized distorted Toward Direct Enantiomers SERS Discrimination. ACS Appl. Mater. heptagon-containing nanographenes. Chem. Sci. 2017, 8, 1068−1074. Interfaces 2019, 11, 1555−1562. ́ (g) Fujikawa, T.; Segawa, Y.; Itami, K. Laterally π-Extended (9) (a) Kiran, V.; Mathew, S. P.; Cohen, S. R.; Hernandez Delgado, − Dithia[6]helicenes with Heptagons: Saddle-Helix Hybrid Molecules. I.; Lacour, J.; Naaman, R. Helicenes A New Class of Organic Spin − J. Org. Chem. 2017, 82, 7745−7749. (h) Ammon, F.; Sauer, S. T.; Filter. Adv. Mater. 2016, 28, 1957 1962. (b) Kettner, M.; Maslyuk, V. ̈ Lippert, R.; Lungerich, D.; Reger, D.; Hampel, F.; Jux, N. Unexpected V.; Nurenberg, D.; Seibel, J.; Gutierrez, R.; Cuniberti, G.; Ernst, K.- formation of [5]helicenes from hexaarylbenzenes containing pyrrole H.; Zacharias, H. Chirality-Dependent Electron Spin Filtering by moieties. Org. Chem. Front. 2017, 4, 861−870. (i) Fernandez-García,́ Molecular Monolayers of Helicenes. J. Phys. Chem. Lett. 2018, 9, − J. M.; Evans, P. J.; Medina Rivero, S.; Fernandez,́ I.; García- 2025 2030. Fresnadillo, D.; Perles, J.; Casado, J.; Martín, N. π-Extended (10) Tanaka, H.; Ikenosako, M.; Kato, Y.; Fujiki, M.; Inoue, Y.; Corannulene-Based Nanographenes: Selective Formation of Negative Mori, T. Symmetry-based rational design for boosting chiroptical Curvature. J. Am. Chem. Soc. 2018, 140, 17188−17196. (j) Cruz, C. responses. Commun. Chem. 2018, 1, 38. M.; Castro-Fernandez,́ S.; Macô̧as, E.; Cuerva, J. M.; Campaña, A. G. (11) Nakai, Y.; Mori, T.; Inoue, Y. Theoretical and Experimental Studies on Circular Dichroism of Carbo[n]helicenes. J. Phys. Chem. A Undecabenzo[7]superhelicene: A Helical Nanographene Ribbon as a − Circularly Polarized Luminescence Emitter. Angew. Chem., Int. Ed. 2012, 116, 7372 7385. 2018, 57, 14782−14786. (k) Hsieh, Y.-C.; Wu, C.-F.; Chen, Y.-T.; (12) Li, C.; Yang, Y.; Miao, Q. Recent Progress in Chemistry of Multiple Helicenes. Chem. - Asian J. 2018, 13, 884−894. Fang, C.-T.; Wang, C.-S.; Li, C.-H.; Chen, L.-Y.; Cheng, M.-J.; Chueh, (13) (a) Laarhoven, W. H.; Cuppen, T. H. J. M. Photo- C.-C.; Chou, P.-T.; Wu, Y.-T. 5,14-Diaryldiindeno[2,1-f:1′,2′ -j]- dehydrocyclizations of stilbene-like compounds VII: Synthesis and picene: A New Stable [7]Helicene with a Partial Biradical Character. properties of the double helicene, diphenanthro[3,4-c;3′,4′-l]- J. Am. Chem. Soc. 2018, 140, 14357−14366. (l) Reger, D.; Haines, P.; chrysene. Recl. Trav. Chim. Pay-B 1973, 92, 553−562. (b) Lütke Heinemann, F. W.; Guldi, D. M.; Jux, N. Oxa[7]superhelicene: A π- Eversloh, C.; Liu, Z.; Müller, B.; Stangl, M.; Li, C.; Müllen, K. Core- Extended Helical Chromophore Based on Hexa-peri-hexabenzocor- − Extended Terrylene Tetracarboxdiimide: Synthesis and Chiroptical onenes. Angew. Chem., Int. Ed. 2018, 57, 5938 5942. (m) Nakakuki, Characterization. Org. Lett. 2011, 13, 5528−5531. (c) Luo, J.; Xu, X.; Y.; Hirose, T.; Sotome, H.; Miyasaka, H.; Matsuda, K. Hexa-peri- π π Mao, R.; Miao, Q. Curved Polycyclic Aromatic Molecules That Are - hexabenzo[7]helicene: Homogeneously -Extended Helicene as a Isoelectronic to Hexabenzocoronene. J. Am. Chem. Soc. 2012, 134, Primary Substructure of Helically Twisted Chiral Graphenes. J. Am. − − 13796 13803. (d) Xiao, S.; Kang, S. J.; Wu, Y.; Ahn, S.; Kim, J. B.; Chem. Soc. 2018, 140, 4317 4326. (n) Cruz, C. M.; Marquez, I. R.; Loo, Y.-L.; Siegrist, T.; Steigerwald, M. L.; Li, H.; Nuckolls, C. Mariz, I. F. A.; Blanco, V.; Sanchez-Sanchez, C.; Sobrado, J. M.; Supersized contorted aromatics. Chem. Sci. 2013, 4, 2018−2023. Martin-Gago, J. A.; Cuerva, J. M.; Macoas, E.; Campana, A. G. (e) Arslan, H.; Uribe-Romo, F. J.; Smith, B. J.; Dichtel, W. R. Enantiopure distorted ribbon-shaped nanographene combining two- Accessing extended and partially fused hexabenzocoronenes using a photon absorption-based upconversion and circularly polarized benzannulation−cyclodehydrogenation approach. Chem. Sci. 2013, 4, luminescence. Chem. Sci. 2018, 9, 3917−3924. (o) Evans, P. J.; − ́ ́ 3973 3978. (f) Bock, H.; Huet, S.; Dechambenoit, P.; Hillard, E. A.; Ouyang, J.; Favereau, L.; Crassous, J.; Fernandez, I.; Perles Hernaez, Durola, F. From Chrysene to Double [5]Helicenes. Eur. J. Org. Chem. J.; Martin, N. Synthesis of a Helical Bilayer Nanographene. Angew. 2015, 2015, 1033−1039. (g) Fujikawa, T.; Segawa, Y.; Itami, K. − Chem., Int. Ed. 2018, 57, 6774 6779. (p) Kato, K.; Furukawa, K.; Synthesis, Structures, and Properties of π-Extended Double Helicene: Mori, T.; Osuka, A. Porphyrin-Based Air-Stable Helical Radicals. A Combination of Planar and Nonplanar π-Systems. J. Am. Chem. Soc. − Chem. - Eur. J. 2018, 24, 572 575. (q) Milton, M.; Schuster, N. J.; 2015, 137, 7763−7768. (h) Kashihara, H.; Asada, T.; Kamikawa, K. ́ ́ Paley, D. W.; Hernandez Sanchez, R.; Ng, F.; Steigerwald, M. L.; Synthesis of a Double Helicene by a Palladium-Catalyzed Cross- Nuckolls, C. Defying strain in the synthesis of an electroactive bilayer Coupling Reaction: Structure and Physical Properties. Chem. - Eur. J. helicene. Chem. Sci. 2019, 10, 1029−1034. (r) Bam, R.; Yang, W.; 2015, 21, 6523−6527. (i) Yang, Y.; Yuan, L.; Shan, B.; Liu, Z.; Miao, Longhi, G.; Abbate, S.; Lucotti, A.; Tommasini, M.; Franzini, R.; Q. Twisted Polycyclic Arenes from Tetranaphthyldiphenylbenzenes Villani, C.; Catalano, V. J.; Olmstead, M. M.; Chalifoux, W. A. Four- by Controlling the Scholl Reaction with Substituents. Chem. - Eur. J. Fold Alkyne Benzannulation: Synthesis, Properties, and Structure of 2016, 22, 18620−18627. (j) Hu, Y.; Wang, X.-Y.; Peng, P.-X.; Wang, Pyreno[a]pyrene-Based Helicene Hybrids. Org. Lett. 2019, 21, 8652− X.-C.; Cao, X.-Y.; Feng, X.; Müllen, K.; Narita, A. Benzo-Fused 8656. (s) Pedersen, S. K.; Eriksen, K.; Pittelkow, M. Symmetric, Double [7]Carbohelicene: Synthesis, Structures, and Physicochemical Unsymmetrical, and Asymmetric [7]-, [10]-, and [13]Helicenes. Properties. Angew. Chem., Int. Ed. 2017, 56, 3374−3378. (k) Fujikawa, Angew. Chem., Int. Ed. 2019, 58, 18419−18423. T.; Mitoma, N.; Wakamiya, A.; Saeki, A.; Segawa, Y.; Itami, K. (4) (a) Kiel, G. R.; Patel, S. C.; Smith, P. W.; Levine, D. S.; Tilley, T. Synthesis, properties, and crystal structures of π-extended double D. Expanded Helicenes: A General Synthetic Strategy and [6]helicenes: contorted multi-dimensional stacking lattice. Org. Remarkable Supramolecular and Solid-State Behavior. J. Am. Chem. Biomol. Chem. 2017, 15, 4697−4703. (l) Satoh, M.; Shibata, Y.; Soc. 2017, 139, 18456−18459. (b) Nakakuki, Y.; Hirose, T.; Matsuda, Tanaka, K. Enantioselective Synthesis of Fully Benzenoid Single and K. Synthesis of a Helical Analogue of Kekulene: A Flexible π- Double Carbohelicenes via Gold-Catalyzed Intramolecular Hydro- Expanded Helicene with Large Helical Diameter Acting as a Soft arylation. Chem. - Eur. J. 2018, 24, 5434−5438. (m) Hu, Y.; Paterno,̀ Molecular Spring. J. Am. Chem. Soc. 2018, 140, 15461−15469. G.M.;Wang,X.-Y.;Wang,X.-C.;Guizzardi,M.;Chen,Q.; (5) (a) OuYang, J.; Crassous, J. Chiral multifunctional molecules Schollmeyer, D.; Cao, X.-Y.; Cerullo, G.; Scotognella, F.; Müllen, based on organometallic helicenes: Recent advances. Coord. Chem. K.; Narita, A. π-Extended Pyrene-Fused Double [7]Carbohelicene as Rev. 2018, 376, 533−547. (b) Dhbaibi, K.; Favereau, L.; Crassous, J. a Chiral Polycyclic Aromatic Hydrocarbon. J. Am. Chem. Soc. 2019,

7072 https://dx.doi.org/10.1021/jacs.0c00646 J. Am. Chem. Soc. 2020, 142, 7066−7074 Journal of the American Chemical Society pubs.acs.org/JACS Article

141, 12797−12803. (n) Kimura, Y.; Shibata, Y.; Noguchi, K.; Tanaka, Marquez,́ I. R.; Castro-Fernandez,́ S.; Cuerva, J. M.; Macô̧as, E.; K. Enantioselective Synthesis and Epimerization Behavior of a Chiral Campaña, A. G. A Triskelion-Shaped Saddle-Helix Hybrid Nano- S-Shaped [11]Helicene-Like Molecule Having Collision between graphene. Angew. Chem., Int. Ed. 2019, 58, 8068−8072. (l) Roy, M.; Terminal Benzene Rings. Eur. J. Org. Chem. 2019, 2019, 1390−1396. Berezhnaia, V.; Villa, M.; Vanthuyne, N.; Giorgi, M.; Naubron, J.-V.; (14) (a) Liu, X.; Yu, P.; Xu, L.; Yang, J.; Shi, J.; Wang, Z.; Cheng, Y.; Poyer, S.; Monnier, V.; Charles, L.; Carissan, Y.; Hagebaum-Reignier, Wang, H. Synthesis for the Mesomer and Racemate of Thiophene- D.; Rodriguez, J.; Gingras, M.; Coquerel, Y. Stereoselective Syntheses, Based Double Helicene under Irradiation. J. Org. Chem. 2013, 78, Structures and Properties of Extremely Distorted Chiral Nano- 6316−6321. (b) Nakamura, K.; Furumi, S.; Takeuchi, M.; Shibuya, graphenes Embedding Hextuple Helicenes. Angew. Chem., Int. Ed. T.; Tanaka, K. Enantioselective Synthesis and Enhanced Circularly 2020, 59, 3264−3271. Polarized Luminescence of S-Shaped Double Azahelicenes. J. Am. (17) (a) Li, Y.; Wang, C.; Li, C.; Di Motta, S.; Negri, F.; Wang, Z. Chem. Soc. 2014, 136, 5555−5558. (c) Sakamaki, D.; Kumano, D.; Synthesis and Properties of Ethylene-Annulated Di(perylene Yashima, E.; Seki, S. A Facile and Versatile Approach to Double N- diimides). Org. Lett. 2012, 14, 5278−5281. (b) Khokhlov, K.; Heterohelicenes: Tandem Oxidative C-N Couplings of N-Hetero- Schuster, N. J.; Ng, F.; Nuckolls, C. Functionalized Helical Building acenes via Cruciform Dimers. Angew. Chem., Int. Ed. 2015, 54, 5404− Blocks for Nanoelectronics. Org. Lett. 2018, 20, 1991−1994. 5407. (d) Sakamaki, D.; Kumano, D.; Yashima, E.; Seki, S. Chem. (c) Nowak-Krol,́ A.; Würthner, F. Progress in the synthesis of Commun. 2015, 51, 17237−17240 A double hetero[4]helicene perylene bisimide dyes. Org. Chem. Front. 2019, 6, 1272−1318. composed of two phenothiazines: synthesis, structural properties, (18) (a) Zhong, Y.; Kumar, B.; Oh, S.; Trinh, M. T.; Wu, Y.; Elbert, and cationic states. (e) Katayama, T.; Nakatsuka, S.; Hirai, H.; K.; Li, P.; Zhu, X.; Xiao, S.; Ng, F.; Steigerwald, M. L.; Nuckolls, C. Yasuda, N.; Kumar, J.; Kawai, T.; Hatakeyama, T. Two-Step Synthesis Helical Ribbons for Molecular Electronics. J. Am. Chem. Soc. 2014, of Boron-Fused Double Helicenes. J. Am. Chem. Soc. 2016, 138, 136, 8122−8130. (b) Sisto, T. J.; Zhong, Y.; Zhang, B.; Trinh, M. T.; 5210−5213. (f) Wang, X.-Y.; Wang, X.-C.; Narita, A.; Wagner, M.; Miyata, K.; Zhong, X.; Zhu, X.-Y.; Steigerwald, M. L.; Ng, F.; Cao, X.-Y.; Feng, X.; Müllen, K. Synthesis, Structure, and Chiroptical Nuckolls, C. Long, Atomically Precise Donor-Acceptor Cove-Edge Properties of a Double [7]Heterohelicene. J. Am. Chem. Soc. 2016, Nanoribbons as Electron Acceptors. J. Am. Chem. Soc. 2017, 139, 138, 12783−12786. (g) Shu, C.; Zhang, H.; Olankitwanit, A.; Rajca, 5648−5651. (c) Gao, G.; Liang, N.; Geng, H.; Jiang, W.; Fu, H.; S.; Rajca, A. High-Spin Diradical Dication of Chiral π-Conjugated Feng, J.; Hou, J.; Feng, X.; Wang, Z. Spiro-Fused Perylene Diimide Double Helical Molecule. J. Am. Chem. Soc. 2019, 141, 17287−17294. Arrays. J. Am. Chem. Soc. 2017, 139, 15914−15920. (d) Peurifoy, S. (h) Sun, Z.; Yi, C.; Liang, Q.; Bingi, C.; Zhu, W.; Qiang, P.; Wu, D.; R.; Castro, E.; Liu, F.; Zhu, X.-Y.; Ng, F.; Jockusch, S.; Steigerwald, M. Zhang, F. π-Extended C2-Symmetric Double NBN-Heterohelicenes L.; Echegoyen, L.; Nuckolls, C.; Sisto, T. J. Three-Dimensional with Exceptional Luminescent Properties. Org. Lett. 2020, 22, 209− Graphene Nanostructures. J. Am. Chem. Soc. 2018, 140, 9341−9345. 213. (e) Wu, M.; Xia, P.; Huang, H.; Lin, Z.; You, X.; Wang, K.; Lu, H.; (15) (a) Zhu, Y.; Guo, X.; Li, Y.; Wang, J. Fusing of Seven HBCs Wu, D.; Xia, J. π-Extension improves the photovoltaic performance: toward a Green Nanographene Propeller. J. Am. Chem. Soc. 2019, 141, helical perylene diimide oligomer based three-dimensional non- 5511−5517. (b) Navakouski, M.; Zhylitskaya, H.; Chmielewski, P. J.; fullerene acceptor. Mater. Chem. Front. 2019, 3, 2414−2420. Lis, T.; Cybinska,́ J.; Stępien,́ M. Stereocontrolled Synthesis of Chiral (19) Schuster, N. J.; Hernandeź Sanchez,́ R.; Bukharina, D.; Kotov, Heteroaromatic Propellers with Small Optical Bandgaps. Angew. N. A.; Berova, N.; Ng, F.; Steigerwald, M. L.; Nuckolls, C. A Helicene Chem. 2019, 131, 4983−4987. Nanoribbon with Greatly Amplified Chirality. J. Am. Chem. Soc. 2018, (16) (a) Saito, H.; Uchida, A.; Watanabe, S. Synthesis of a Three- 140, 6235−6239. Bladed Propeller-Shaped Triple [5]Helicene. J. Org. Chem. 2017, 82, (20) Very few molecules have Δε in the visible range of 103 M−1 5663−5668. (b) Berezhnaia, V.; Roy, M.; Vanthuyne, N.; Villa, M.; cm−1, and of these molecules, none has Δε exceeding 1100 M−1 cm−1. Naubron, J.-V.; Rodriguez, J.; Coquerel, Y.; Gingras, M. Chiral (a) Werner, A.; Michels, M.; Zander, L.; Lex, J.; Vogel, E. Figure Nanographene Propeller Embedding Six Enantiomerically Stable Eight” Cyclooctapyrroles: Enantiomeric Separation and Determina- [5]Helicene Units. J. Am. Chem. Soc. 2017, 139, 18508−18511. tion of the Absolute Configuration of a Binuclear Metal Complex. (c) Hosokawa, T.; Takahashi, Y.; Matsushima, T.; Watanabe, S.; Angew. Chem., Int. Ed. 1999, 38, 3650−3653. (b) Sugiura, H.; Kikkawa, S.; Azumaya, I.; Tsurusaki, A.; Kamikawa, K. Synthesis, Nigorikawa, Y.; Saiki, Y.; Nakamura, K.; Yamaguchi, M. Marked Effect Structures, and Properties of Hexapole Helicenes: Assembling Six of Aromatic Solvent on Unfolding Rate of Helical Ethynylhelicene [5]Helicene Substructures into Highly Twisted Aromatic Systems. J. Oligomer. J. Am. Chem. Soc. 2004, 126, 14858−14864. (c) Brahma, Am. Chem. Soc. 2017, 139, 18512−18521. (d) Zhu, Y.; Xia, Z.; Cai, S.; Ikbal, S. A.; Dhamija, A.; Rath, S. P. Highly Enhanced Bisignate Z.; Yuan, Z.; Jiang, N.; Li, T.; Wang, Y.; Guo, X.; Li, Z.; Ma, S.; Circular Dichroism of Ferrocene-Bridged Zn(II) Bisporphyrin Zhong, D.; Li, Y.; Wang, J. Synthesis and Characterization of Tweezer with Extended Chiral Substrates due to Well-Matched Hexapole [7]Helicene, A Circularly Twisted Chiral Nanographene. J. Host−Guest System. Inorg. Chem. 2014, 53, 2381−2395. (d) Sato, S.; Am. Chem. Soc. 2018, 140, 4222−4226. (e) Tanaka, H.; Kato, Y.; Yoshii, A.; Takahashi, S.; Furumi, S.; Takeuchi, M.; Isobe, H. Chiral Fujiki, M.; Inoue, Y.; Mori, T. Combined Experimental and Intertwined Spirals and Magnetic Transition Dipole Moments Theoretical Study on Circular Dichroism and Circularly Polarized Dictated by Cylinder Helicity. Proc. Natl. Acad. Sci. U. S. A. 2017, Luminescence of Configurationally Robust D3-Symmetric Triple 114, 13097−13101. (e) Wang, J.; Zhuang, G.; Chen, M.; Lu, D.; Li, Pentahelicene. J. Phys. Chem. A 2018, 122, 7378−7384. (f) Zhang, F.; Z.; Huang, Q.; Jia, H.; Cui, S.; Shao, X.; Yang, S.; Du, P. Selective Michail, E.; Saal, F.; Krause, A.; Ravat, P. Combined Experimental Synthesis of Conjugated Chiral Macrocycles: Sidewall Segments of and Theoretical Study on Circular Dichroism and Circularly Polarized (−)/(+)-(12,4) Carbon Nanotubes with Strong Circularly Polarized Luminescence of Configurationally Robust D3-Symmetric Triple Luminescence. Angew. Chem., Int. Ed. 2020, 59, 1619−1626. Pentahelicene. Chem. - Eur. J. 2019, 25, 16241−16245. (g) Liu, G.; (21) Pescitelli, G.; Di Bari, L.; Berova, N. Conformational aspects in Koch, T.; Li, Y.; Doltsinis, N. L.; Wang, Z. Nanographene Imides the studies of organic compounds by electronic circular dichroism. Featuring Dual Core Sixfold [5]Helicenes. Angew. Chem., Int. Ed. Chem. Soc. Rev. 2011, 40, 4603−4625. 2019, 58, 178−183. (h) Meng, D.; Liu, G.; Xiao, C.; Shi, Y.; Zhang, (22) We used SpecDis to render the TDDFT-calculated UV-visible L.; Jiang, L.; Baldridge, K. K.; Li, Y.; Siegel, J. S.; Wang, Z. absorbance and ECD spectra: Bruhn, T.; Schaumlöffel, A.; Corannurylene Pentapetalae. J. Am. Chem. Soc. 2019, 141, 5402− Hemberger, Y.; Bringmann, G. SpecDis: Quantifying the Comparison 5408. (i) Wang, Y.; Yin, Z.; Zhu, Y.; Gu, J.; Li, Y.; Wang, J. Hexapole of Calculated and Experimental Electronic Circular Dichroism [9]Helicene. Angew. Chem., Int. Ed. 2019, 58, 587−591. (j) Guo, X.; Spectra. Chirality 2013, 25, 243−249. Yuan, Z.; Zhu, Y.; Li, Z.; Huang, R.; Xia, Z.; Zhang, W.; Li, Y.; Wang, (23) (a) Laarhoven, W. H.; de Jong, M. H. Photodehydrocycliza- J. Nitrogen-Doped Hexapole [7]Helicene vs Its All-Carbon Analogue. tions of stilbene-like compounds VIII: Synthesis of hexaheliceno[3,4- Angew. Chem., Int. Ed. 2019, 58, 16966−16972. (k) Cruz, C. M.; c]hexahelicene. Recl. Trav. Chim. Pay-B 1973, 92,651−657.

7073 https://dx.doi.org/10.1021/jacs.0c00646 J. Am. Chem. Soc. 2020, 142, 7066−7074 Journal of the American Chemical Society pubs.acs.org/JACS Article

(b) Laarhoven, W. H.; Cuppen, T. J. H. M.; Nivard, R. J. F. Photodehydrocyclizations of stilbene-like compounds−XI: Synthesis and racemization of the double helicene diphenanthro[4.3-a;3′.4′- o]picene. Tetrahedron 1974, 30, 3343−3347. (c) Martin, R. H.; Eyndels, C.; Defay, N. Double helicenes: Diphenanthro[4,3-a;3′,4′- o]picene and benzo[s]diphenanthro[4,3-a;3′,4′-o]picene. Tetrahedron 1974, 30, 3339−3342.

7074 https://dx.doi.org/10.1021/jacs.0c00646 J. Am. Chem. Soc. 2020, 142, 7066−7074