A Three-Step Sequence Strategy for Facile Construction of Donor-Acceptor Type Molecules: Triphenylamine- Substituted Acenes
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Canadian Journal of Chemistry A Three-step Sequence Strategy for Facile Construction of Donor-Acceptor Type Molecules: Triphenylamine- Substituted Acenes Journal: Canadian Journal of Chemistry Manuscript ID cjc-2019-0254.R1 Manuscript Type: Article Date Submitted by the 21-Sep-2019 Author: Complete List of Authors: Zhang, Chen; Wuhan University of Technology, chemical Engineering and Life Sciences Tang, Ming; Wuhan University of Technology, chemical Engineering and Life SciencesDraft Sun, Bing; Wuhan University of Technology, chemical Engineering and Life Sciences Wang, Weizhou; Wuhan University of Technology, chemical Engineering and Life Sciences Yi, Ying; Wuhan University of Technology, chemical Engineering and Life Sciences Zhang, Fang-Lin; Wuhan University of Technology, chemical Engineering and Life Sciences Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue?: Keyword: triphenylamine, anthracene, C–H activation, fluorescence https://mc06.manuscriptcentral.com/cjc-pubs Page 1 of 14 Canadian Journal of Chemistry 1 A Three-step Sequence Strategy for Facile Construction of Donor-Acceptor Type Molecules: Triphenylamine-Substituted Acenes Chen Zhang, Ming Tang, Bing Sun, Weizhou Wang, Ying Yi and Fang-Lin Zhang Chen Zhang, Ming Tang, Bing Sun, Ying Yi and Fang-Lin Zhang. chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, Hubei, PR China. Weizhou Wang. College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal University, Luoyang 471934, PR China. Corresponding authors: Weizhou Wang (e-mail: [email protected]), Ying Yi (e-mail: [email protected]) and Fang-Lin Zhang (e-mail: [email protected]) Draft https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 2 of 14 2 Abstract: A new synthetic strategy was successfully developed for highly efficient construction of triphenylamine-substituted polycyclic aromatic hydrocarbons (PAHs), including anthracenes, tetraphenes, pentaphenes and trinaphthylene. These molecules exhibited special structural characteristics, including donor-acceptor-donor (D-A-D) and donor-acceptor (D-A). Diverse aryl iodides coupled well with chlorinated 2-methyl benzaldehydes via a transient ligand-directed C–H bond arylation strategy to furnish various PAH precursors. The subsequent palladium-catalyzed Suzuki cross-couplings with 4-(diphenylamino)phenylboronic acid produced corresponding triphenylamine derivatives. Further Brønsted acid-promoted cycloaromatization generated the triphenylamine-substituted PAHs readily. The photophysical properties was investigated by UV-visible absorption and fluorescence emission spectroscope together with density functional theory (DFT) calculations. Key words: triphenylamine, anthracene, C–H activation, fluorescence. Draft https://mc06.manuscriptcentral.com/cjc-pubs Page 3 of 14 Canadian Journal of Chemistry 3 Introduction Due to their unique molecular structure and optical property, organic conjugated molecules bearing donor–acceptor (D-A) system are widely used as photoelectron materials in the area of organic solar cells, organic light-emitting diodes (OLEDs), sensors, data storage displays and organic crystal field-effect transistors (OFETs) etc1-6. The diverse combinations of various donor and acceptor moieties endow these systems easily tunable highest occupied molecular orbital (HOMO) energy levels and lowest unoccupied molecular orbital (LUMO) energy levels, adjustable optical bandgap, large π-conjugation length, intramolecular charge transfer and strong π-π stacking interactions5,7, which contribute to the readily tunable optical and electrical properties of the hole-transporting materials (HTMs). Triphenylamine (TPA) group proves to be a widely used donor unit for construction of opto- and electroactive organic small molecules and polymeric materials since it has good electron donating and hole-transporting property as well as special nonplanar propeller starburst molecular shape8-10. Polycyclic aromatic hydrocarbons (PAHs), such as anthracenes11, phenanthrenes12, pyrenes13 and tetracenes14, exhibit excellent fluorescence characteristics and have been introduced into the D- A system to improve the photoelectric properties like color purity and electroluminescence (EL) efficiency of materials15. Literature survey showed that a variety of D-A configuration molecules with TPA as donor moiety and PAHs as acceptor moieties have been prepared. For instance, in 2016, Putala group6 reported a series of D-A system molecules featuring TPA and analogues connecting to different positions of the aromatic ring cores by alkyne. In 2017, Hariharan etc.16 synthesized a set of twisting D-A molecules with TPA as donor, aromatic hydrocarbons include benzene (Ph), naphthalene (Nap), anthracene (An), phenanthrene (Phe) and pyrene (Py) as acceptor via the Suzuki-Miyaura cross-couplings with aryl (Ph, Nap, An, Phe and Py) boronic acids. The dual-core derivatives of TPA end-capped anthracence and pyrene were also constructed using two-step Suzuki couplings13,15. Furthermore, the TPA unit cooperated with PAHs were applied to build copolymer macromolecules through coupling interactions17. Most of them used anthracene as core and introduced TPA moiety into the C-9 and/or C-10 positions by Suzuki-Miyaura couplings starting from commercially available halogenated polyacenes18-26. However, other polycyclic segments are rarely utilized because of the expensive costs or exhausting synthetic processes of PAHs, especially with extensive fused aromatic rings14,27. To circumvent the above limitations, our previous work developed a highly efficient two-step strategy to readily construct PAHs28,29 (Scheme 1). The first step proceeded via a transient directing group enabled palladium-catalyzed ortho-C(sp3)–H arylation of benzaldehydes, while the second step involvedDraft a Brønsted acid-promoted cycloaromatization27,30. In this work, D- A-D and D-A arrays end-capped with one or more TPA as donor units were elaborately designed and facilely synthesized. The highly efficient cascade arylations and cycloaromatizations of Our previous work: O I 1) Pd(OAc)2 via: transient DG O I N O I 2) TfOH Pd H OAc This work: Donor Donor R R I O 1) Pd(OAc)2 transient DG I TPA4BA I 2) cross-coupling Cl 3) TfOH Donor R Donor: R = N N Scheme 1. Synthesis of TPA derivatives. benzaldehydes with halides provided a series of PAHs, including anthracene, tetraphene, pentaphene and trinaphthylene, which served as acceptor units. Particularly, the trinaphthylene molecule as a central core decorated with three TPA groups at 2, 8 and 14-positions formed a special nonplanar propeller star-shaped structure31. Result and Discussion Synthesis of donor-acceptor type molecules Based on our previous work, a new three steps synthetic route to prepare TPA derivatives with polyacene core was developed28,29. First, a transient directing group enabled palladium-catalyzed ortho-C(sp3)–H arylation of benzaldehyde 6 with iodobenzenes afforded the precursor 7. Subsequent Suzuki cross-couplings with 4-(diphenylamino)phenylboronic acid (TPA4BA) produced corresponding triphenylamine derivatives 8. Further cycloaromatization by treatment with trifluoromethanesulfonic acid (TfOH) generated TPA derivatives with D-A array. TPA derivatives combined with anthracene core were widely utilized as organic functional materials3,19. However, those previous anthracene derivatives mainly restricted on the highly reactive C-9 or C-10 position of anthracene32. Herein, we obtained new anthracene derivatives with TPA group on the C-2 or C-6 position (Scheme 2). These derivatives contain electron-donating group (methyl) and electron withdrawing group (chloride). Furthermore, the chloride substituent allowed readily derivatizations via cross-coupling reactions. Then, this new three-step sequence strategy were further extended to the synthesis of tetraphene derivatives. By using of 2- iodonaphthalene as coupling partner, D-A molecule 2a and the acceptor tetraphene was successfully synthesized (Scheme 3). The tetracene derivatives with methyl at C-9 position (2b) was also obtained in good yield. https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 4 of 14 4 To further explore the substrate scope, 1,4-diiodobenzene was examined to construct TPA derivatives bearing a pentaphene segment (Scheme 4). The D-A-D molecule 3a with pentaphene core was constructed by using TfOH as cycloaromatization reagent. In addition, D-A-D molecules with TPA groups on C-1, C-12 and C-2, C-10 positions (3b & 3c) were also successfully incorporated. Pd(OAc) O 2 O AgTFA I glycine X AcOH/H2O (v/v=9/1) X 1 R1 (70%-74%) R 5 6 7 1 O R TPA4BA TfOH 2 cross-coupling R (54%-73%) 1 (56%-73%) R R2 8 1 N N 1a 1b Cl N 1c Scheme 2. Synthesis of TPA derivatives with anthracene as acceptor unit. O Pd(OAc)2 O AgTFA I glycine H (Br) H (Br) AcOH/H2O (v/v=9/1) Cl (Me) (72%-73%) Cl (Me) 5 6 7 Draft O (Me) R TPA4BA TfOH cross-coupling H (R) (70%-77%) (68%) R (Me) H (R) 8 2 N N 2a 2b Scheme 3. Synthesis of TPA derivatives with tetraphene as acceptor unit. Pd(OAc) O 2 AgTFA I (Me)Cl O glycine Cl(Me) I AcOH/H2O (v/v=9/1) (Me)Cl (52%-66%) O 5 6 7 R R O TPA4BA O TfOH R cross-coupling R (80%-82%) (66%-85%) 8 3 N N N 3a N N N 3c 3b Scheme 4. Synthesis of TPA derivatives with pentaphene as acceptor unit. https://mc06.manuscriptcentral.com/cjc-pubs Page 5 of 14 Canadian Journal of Chemistry 5 Recently, star-shaped π-conjugated