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. 2024 Aug 13;2(9):488–494. doi: 10.1021/prechem.4c00038

Quadruple[6]Helicene Featuring Pyrene Core: Unraveling Contorted Aromatic Core with Larger Effective Conjugation

Christopher Wallerius †, Otgonbayar Erdene-Ochir †, Eva Van Doeselar †, Ronald Alle †, Anh Tu Nguyen ‡, Marvin F Schumacher ‡, Arne Lützen ‡, Klaus Meerholz †, Sai Ho Pun †,*
PMCID: PMC11501045  PMID: 39474393

Abstract

graphic file with name pc4c00038_0007.jpg

Multiple helicenes display distinct aromatic cores characterized by highly twisted rings that are shared or fused with constituent helicene moieties. Diversifying these aromatic cores unlocks avenues for creating multiple helicenes with distinct properties and topologies. Herein we report the synthesis of a quadruple[6]helicene featuring pyrene as the aromatic core. The synthesis involved key steps of the annulative π-extension reaction and Scholl reaction. By extending multiple helicenes along the axial direction, the degree of contortion of the aromatic core can be controlled from nearly flat to highly twisted. Notably, quadruple[6]helicene exhibits a significant red-shift of 0.49 eV compared to quadruple[4]helicenes, of which the red-shift arises from both π-extension and augmented effective conjugation due to enhanced twisting. Quantum chemical calculations demonstrate that the degree of contortion in the pyrene core adeptly governs the energy levels of the HOMO and LUMO, which offers an alternative strategy beyond mere enlargement of the π backbone. An intriguing serendipitous finding reveals the formation of one-molecule-thick supramolecular homochiral nanosheets through self-interlocking interactions of enantiomers in single crystals, a rare packing motif for multiple helicenes.

Keywords: Helicenes, Polycyclic aromatics, Pyrene, Core contortion, Effective conjugation

Introduction

The emergence of multiple helicenes has garnered significant attention owing to π-extended structures and helical chirality.1 Multiple helicenes, characterized by the incorporation of plural helicene moieties within a single polycyclic aromatic framework, have emerged as a fascinating class of molecules distinct from their single helicene counterparts.2−4 Their appeal lies in their ability to exhibit unique π–π stacking motifs5−8 and enhances chiroptical responses in the visible region,1,9 offering exciting opportunities in the realm of circularly polarized light detection10,11 and emission.12,13 One defining characteristic of multiple helicene molecules is their distinct aromatic core, often comprising highly twisted ring(s) that are commonly shared or fused by the constituent helicene moieties.2,14 For example, double[7]helicene 1(15) features a highly twisted benzene ring at its core16−25 (Figure 1a, highlighted in pink). Higher order multiple helicenes can be accessed by employing larger symmetric π-systems as core, such as quadruple helicene 2,26 featuring a naphthalene core27−29 (Figure 1b, highlighted in pink). Recent advancements have expanded the repertoire of aromatic cores to include corannulene,30−35 hexabenzocoronene,36−39 and perylene,40,41 resulting in π-conjugated systems with unique properties like near-infrared absorption and emission,40 high fluorescence quantum yields,41 and strong Cotton effect.42 Diversifying aromatic cores for multiple helicenes holds great promise for synthesizing novel π-extended structures and exploring distinct photophysical and chiroptical properties.

Figure 1.

Figure 1

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(a) Double[7]helicenes 1 with the twisted benzene core highlighted in pink; (b) Quadruple helicene 2 with the twisted naphthalene core highlighted in pink; (c) Quadruple[6]helicenes 3 with the pyrene core highlighted in blue.

Pyrene is a versatile building block renowned for its intricate photophysical properties.43,44 When incorporated into the core of multiple helicenes, these helicenes potentially inherit the intriguing photophysical properties of pyrene. Previous studies on multiple helicenes featuring pyrene core,45−47 primarily based on [4]helicenes, have been impeded by low racemization barriers, limiting comprehensive investigations into the captivating chiroptical properties exhibited by pyrene-based multiple helicenes. In this study, we synthesized a new quadruple[6]helicene 3 by introducing four [6]helicene moieties sharing the central pyrene core (Figure 1c, highlighted in blue). The fusion of [6]helicene units induces a pronounced twisting of the pyrene core, resulting in a larger effective conjugation within the core that effectively modulates the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). This contortion strategy offers an alternative approach beyond the mere enlargement of the π-backbone to tailor the electronic properties of multiple helicenes. Detailed below are the synthesis, structural analysis, stereochemistry, and electronic properties of quadruple[6]helicene 3.

Results and Discussion

Scheme 1a outlines the synthesis of quadruple[6]helicene 3, which commenced with an annulative π-extension (APEX)45,48 reaction between 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrene49 and 3,7-di-tert-butyl-5,5-dimethyl-5H-dibenzo[b,d]silole.50 However, the APEX reaction exhibited a low yield for 4 primarily due to the presence of two major side products resulting from the loss of one or two Bpin groups. To serve as the substrate for the subsequent Scholl reaction, compound 6 was synthesized through a Suzuki cross-coupling between compound 4 and aryl iodide 5.40 Notably, the introduction of methoxy groups to compound 6 facilitated cyclodehydrogenation during the Scholl reaction by lowering the oxidation potential.51 The Scholl reaction of compound 6 under conditions of six equivalents of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and excess methanesulfonic acid52,53 at room temperature for 10 min resulted in a yield of 72% for compound 3. Extending the reaction time did not affect the yield. It is important to highlight that the oxidative cyclodehydrogenation of the [6]helicene moieties to form a heptagon, as reported previously,54 did not occur in compound 3. This observation can be attributed to the primary localization of the spin density at the core pyrene moiety and the absence of spin density at the cyclization sites (Figure S26).55 Quadruple[4]helicene 7(46) (Scheme 1b) was synthesized for comparative analysis of its electronic properties with compound 3. The synthesis of 7 included a Suzuki cross-coupling reaction between an aryl iodide and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrene, followed by a subsequent Scholl reaction. Detailed information regarding the synthesis can be found in the Supporting Information (Scheme S1).

Scheme 1. (a) Synthesis of Quadruple[6]helicene 3; (b) Structure of 7 with the Blue Bonds Formed by Suzuki Cross-Coupling and Red Bonds Formed by Scholl Reaction.

Scheme 1

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Quadruple helicene 3 has six stereoisomers, including two pairs of enantiomers and two meso compounds. The stereoisomers with the helicity of (P, P, P, P) and (M, M, M, M) are of D2 symmetry, while that of (M, P, P, P) and (P, M, M, M) are of C1 symmetry, and meso compounds with the helicity of (P, M, P, M) and (P, P, M, M) are of C2v and C2h symmetry, respectively. The 1H NMR spectrum of 3 in CDCl3 shows four singlets and two doublets in the aromatic region, indicating that 3 possesses either D2 or C2v symmetry (Figure S5) so that the C1 symmetric stereoisomers could be excluded.

Fortunately, the geometry of 3 was further confirmed by an X-ray crystallographic analysis. Single crystals of compound 3 were obtained by slowly diffusing methanol into a CH2Cl2 solution. X-ray crystallography analysis revealed an orthorhombic unit cell containing three pairs of enantiomers of 3, exhibiting the helicity of (P, P, P, and P) and (M, M, M, and M). Figure 2a illustrates one of the enantiomers of 3 with (P, P, P, P) helicity, adopting a propeller-like shape with approximate D2 symmetry. The dihedral angles between the planes defined by the terminal rings of the [6]helicene moieties range from 50.1° to 57.6°, indicating a slightly reduced twist compared to a single [6]helicene with a torsion angle of 59.6°. The fusion of four [6]helicene moieties results in noticeable twisting of the two benzenoid rings within the central pyrene moiety, exhibiting torsion angles of 28.1° (Figure 2b). Remarkably, this level of twisting is significantly larger than those benzenoid rings in the pyrene core of previously reported quadruple helicene with the largest torsion angle up to 3.3°.46Figure 2c,d illustrates the molecular packing observed in the racemic mixture of quadruple helicene 3. In contrast to the typical interaction observed between a pair of enantiomers,5,7 the enantiomers of 3 in the single crystals self-interact and assemble into one-molecule-thick supramolecular homochiral nanosheets.

Figure 2.

Figure 2

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Crystal structure of (rac)-3. All carbon atoms are shown as ellipsoids at 50% probability level, and all hydrogen atoms are removed for clarity. (a) Top view of the polycyclic framework in 3 with the helicity of (P, P, P, P). (b) The central twisted pyrene moiety of 3 in the crystal structure with corresponding torsion angles. (c) Molecular packing of 3 as viewed along the c axis of the unit cell. (d) Molecular packing of 3 as viewed along the b axis of the unit cell.

As shown in Figure 2c, two distinct layers of supramolecular nanosheets are evident: one layer exclusively composed of (P, P, P, P) enantiomers (highlighted in blue), and the other layer consisting solely of (M, M, M, M) enantiomers (highlighted in yellow). There is no discernible void spacing observed between these two homochiral nanosheets. Furthermore, a closer examination along the b-axis of the unit cell (Figure 2d) reveals an interlocking interaction with tert-butyl groups (highlighted in red) from one (P, P, P, P) enantiomer inserting into the vacant space above or below the backbone of an adjacent (P, P, P, P) enantiomer. This leads to edge-to-face interactions with a contact distance of 3.49 Å, measured as the shortest distance between the mean plane of the pyrene core and carbon of the tert-butyl group. Each enantiomer of compound 3 contributed two tert-butyl groups for insertion and simultaneously accepted two tert-butyl groups into the vacant spaces within its own backbone. Consequently, the crystal structure of 3 exhibits a unique two-dimensional56 homochiral stacking, an unprecedented packing motif for multiple helicenes. This intriguing packing pattern may be attributed to the high symmetry of the π-backbone, along with the tert-butyl groups (highlighted in red) facilitating interlocking, and the remaining tert-butyl groups occupying the empty spaces within the nanosheet.

Both compound 7 and compound 3 exhibit limited solubility in chlorinated solvents such as CH2Cl2 and CHCl3, forming an orange solution and a blue solution, respectively. As shown in Figure 3a, the absorption spectrum of 7 in CH2Cl2 reveals a broad absorption band with the absorption peak and shoulder at 502 and 530 nm, respectively. Excitation at 530 nm results in an emission maximum at 554 nm and a fluorescence quantum yield as high as 98%. The absorption spectrum of 3 in CH2Cl2 reveals a broad absorption band ranging from 490 to 660 nm, with the absorption peak at 625 nm. Excitation at 625 nm results in an emission maximum at 651 nm and a fluorescence quantum yield of 64%. To the best of our knowledge, these quantum yields of both compounds 3 and 7 are among the highest for quadruple and higher multiple helicenes, which typically exhibit low photoluminescence quantum yields (<24%)1,32,35,57 The high quantum yields of 3 and 7 can be attributed to their efficient radiative decay processes, as supported by large radiative rate constants of 3.86 × 108 s–1 and 3.57 × 108 s–1 (photoluminescence lifetime 2.52 and 2.74 ns, respectively) and small nonradiative rate constants of 2.17 × 108 s–1 and 7.29 × 106 s–1 respectively (Figure S22 and Table S2). The small Stokes shift of 26 nm (0.08 eV) indicates the limited flexibility of 3, which aligns with the calculations discussed later. The absorption maximum of compound 3 can be attributed to the transition from HOMO to LUMO, occurring at 645 nm with an oscillator strength of 0.5543, as determined from TD-DFT calculations at the B3LYP level with the 6-31G(2d,p) basis set. Notably, the absorption maximum of 3 is red-shifted by 123 nm (0.49 eV) compared to that of 7, primarily due to the expanded π-system over a larger polycyclic framework. The DFT calculations of 7′ and 3′, where tert-butyl groups are replaced by methyl groups to reduce computational cost, reveal the prominent localization of both HOMO and LUMO on the contorted pyrene core (Figures 3b and S27), suggesting that the degree of contortion contributes to the observed redshift of the lowest energy transition.58 To evaluate the impact of the contorted pyrene core, we calculated the frontier molecular orbitals of an imaginary contorted pyrene using the carbon atom coordinates extracted from the optimized structures of 7′ and 3′ at the B3LYP/6-311G(2d,p) level of DFT. As shown in Figure 3c, the optimized flat pyrene displays HOMO and LUMO energy levels of −5.31 and −1.47 eV, respectively. Intriguingly, the contorted pyrene derived from 7′ exhibits orbital lobe overlapping, manifested by an increase in HOMO (−5.13 eV) and a decrease in LUMO (−1.75 eV), suggesting more effective conjugation. Notably, the more contorted pyrene derived from 3′ demonstrates a more pronounced degree of effective conjugation, characterized by a further intensified and apparent overlap of orbital lobes. This configuration features a HOMO energy level of −5.02 eV and a LUMO energy level of −1.89 eV, resulting in a noteworthy reduction of the HOMO–LUMO gap by 0.25 eV compared to that of 7′. These findings underscore the profound impact of extending multiple helicenes along the axial direction, resulting in a more twisted core, on the effective modulation of HOMO and LUMO energy levels.

Figure 3.

Figure 3

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(a) UV/vis absorption spectra (black lines) and photoluminescence spectra (blue lines, excited at 365 nm) of 7 (dashed line) and 3 (solid line) in CH2Cl2 (1 × 10–5 mol L–1). (b) Frontier molecular orbitals of 3′ calculated at the B3LYP/6-31G(d) level of DFT. (c) HOMO and LUMO of pyrene with flat optimized geometry and imaginary contorted geometry (coordinates of carbon atoms extracted from the optimized structure of 7′ and 3′).

Cyclic voltammetry was used to investigate the impact of twisting on the oxidation potentials and to estimate the HOMO energies of the quadruple helicenes.

The cyclic voltammograms of 3 and 7 in CH2Cl2 exhibit two reversible oxidation waves (Figures S24 and S25). Compound 3 shows oxidation potentials at 0.03 and 0.35 V versus ferrocenium/ferrocene, suggesting an estimated HOMO energy level of −5.1 eV.59 In contrast, compound 7 displays oxidation potentials at 0.11 and 0.46 V. The observed decrease in the oxidation potential of compound 3 can be attributed to the presence of electron-donating methoxy groups and the larger effective conjugation of contorted pyrene core, where the HOMO is predominantly localized.

To investigate the thermal stability and stereochemical dynamics of quadruple helicene 3, we performed DFT calculations on the unsubstituted quadruple helicene 3′’ at the B3LYP/6-31G(d) level (Figure 4). The calculations revealed that the enantiomeric (P, P, P, P) and (M, M, M, M) stereoisomers of 3′’ were the most thermodynamically stable, exhibiting lower Gibbs free energy values compared to the other chiral C1 and the meso C2h symmetric diastereomers by 6.0 and 19.5 kcal mol–1, respectively. These energy differences correspond to equilibrium constants of 11.3 × 10–3 and 3.9 × 10–10 at 180 °C. These values are way above previously reported double[6]helicene, which showed a Gibbs free energy difference between chiral and meso diastereomers of only 0.9 kcal mol–1.5 Obviously, incorporating additional [6]helicene moieties in the quadruple helicene structure effectively increases the free energy of the meso diastereomer, explaining the stereoselective formation of the thermodynamically most stable diastereomer of 3.

Figure 4.

Figure 4

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Calculated epimerization steps of 3′′ with relative Gibbs free energy at the B3LYP/6-31G(d) level of DFT.

Further DFT calculations were conducted to analyze the stereoisomerization of quadruple helicene 3′′. The calculations revealed that the helicity inversion of a single [6]helicene moiety (highlighted in yellow) within the (P, P, P, P) stereoisomer proceeds through a transition state (TS1) with an energy barrier of 42.1 kcal mol–1. This barrier corresponds to a rate constant of 4.6 × 10–8 s–1 at 180 °C, as estimated using the Eyring equation (k = κ(kBT/h)exp(−ΔG‡/RT) and the transmission coefficient (κ) is set to 1). Subsequently, the helicity inversion of the second [6]helicene moiety (highlighted in blue) proceeds through TS2 with an energy barrier of 46.9 kcal mol–1. This barrier corresponds to a rate constant of 2.2 × 10–10 s–1 at 180 °C. Therefore, the energy barriers in quadruple helicene 3′′ are higher compared to those reported for [6]helicene and double[6]helicene at the same level of DFT,5 but similar to double[7]helicene.15 Consistent with the computational results, heating of compound 3 at 180 °C in 1,2-dichlorobenzene for 15 h under an inert atmosphere did not induce any changes in the 1H NMR spectrum.

The high isomerization barriers also allowed the successful chiral resolution of compound 3 via high-performance liquid chromatography (HPLC) using a chiral (R,R)-Whelk-O-1 stationary phase (Figures S20 and S21). The first fraction and the second fraction were assigned as (M, M, M, M)-3 and (P, P, P, P)-3, respectively, by comparison of experimentally determined and simulated electronic circular dichroism spectra based on TD-DFT calculations (Figure S28). Circular dichroism (CD) spectropolarimetry measurements of (M, M, M, M)-3 exhibits positive Cotton effect peaks at 269 and 427 nm, while negative Cotton effect peaks are observed at 346 and 631 nm (Figure 5). The CD spectrum of (P, P, P, and P)-3 displayed perfect mirror symmetry, indicating that they are enantiomers with opposite helicity. The molar circular dichroism values (|Δε|) and dissymmetry factors (gCD = |Δε/ε|) for the corresponding transitions were determined as follows: at 269 nm: |Δε| = 258 M–1 cm–1, |gCD| = 5.6 × 10–3; 346 nm: |Δε| = 285 M–1 cm–1, |gCD| = 9.8 × 10–3; 427 nm: |Δε| = 116 M–1 cm–1, |gCD| = 4.7 × 10–3; 631 nm: |Δε| = 21 M–1 cm–1, |gCD| = 8.4 × 10–4. It is worth noting that the largest dissymmetry factors obtained for compound 3 are comparable to [6]helicene60 and higher than the reported quadruple26,40 and sextuple helicenes,24,37 albeit within the same order of magnitude.

Figure 5.

Figure 5

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Circular dichroism spectra of the enantiomers of 3 measured in CH2Cl2. (P, P, P, P)-3 and (M, M, M, M)-3 are shown as red and blue lines, respectively. The UV/vis absorption spectrum of 3 is shown in the background, represented by a gray and shallow profile.

Conclusion

In conclusion, we have successfully synthesized a novel quadruple[6]helicene with pyrene as the aromatic core. Our study revealed an intriguing serendipitous finding—the formation of one-molecule-thick supramolecular homochiral nanosheets through self-interlocking interactions of enantiomers of 3 in single crystals. This quadruple[6]helicene exhibits a high fluorescence quantum yield of 64%, placing it among the highest for quadruple and higher multiple helicenes. Furthermore, it exhibits a significant red-shift of 0.49 eV compared to quadruple[4]helicenes 7 with nearly planar pyrene cores. This redshift can be ascribed to both π-extension and larger effective conjugation resulting from a more twisted pyrene core. These findings highlight the importance of a rational design to manipulate the aromatic core contortion, enabling effective modulation of the energy level of HOMO and LUMO, and offering a viable alternative to the conventional strategy of merely enlarging the π-backbone. Interestingly, the observation of significant redshift resulting from more contorted aromatic cores has also emerged independently in the case of perylene cores, as reported by two separate research groups very recently.40,41 This additional evidence further substantiates the importance of manipulating aromatic core contortion as a means to achieve enhanced conjugation within the core. As a result, these strategies will offer a versatile approach to tailoring the electronic properties by twisting various aromatic cores, thereby opening new avenues for the design of multiple helicenes with tunable properties.

Acknowledgments

We are grateful to Robert Herzhoff and Nora Gildemeister for the help with DFT calculations. We thank Jörg Neudörfl for the single X-ray crystallography. We thank the Regional Computing Center of the University of Cologne (RRZK) for providing computing time on the DFG-funded High Performance Computing (HPC) system CHEOPS.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/prechem.4c00038.

  • Experimental procedures, 1H and 13C NMR spectra, characterization data for all new compounds, optical properties, and computational data (PDF)

  • Crystallographic data of 3 (CIF)

Accession Codes

CCDC 2282129 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif. or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: + 44 1223 336033.

Author Present Address

# Department of Chemistry, Hong Kong University of Science and Technology, Clean Water Bay, Hong Kong

Author Contributions

S.H.P. initiated and conceived the research. S.H.P. and C.W. designed most of the synthesis routes and conducted most of the experiments. S.H.P., O.E., and K.M. conducted UV–vis-NIR absorption, fluorescence, photoluminescence quantum yield measurements. E.V.D. contributed to the synthesis. A.T.N, M.F.S., and A.L. contributed to chiral resolution and circular dichroism measurement. S.H.P. analyzed the data and wrote the manuscript. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

This work was supported by Deutsche Forschungsgemeinschaft (DFG) through RTG 2591 “Template-Designed Organic Electronics”. M.F.S. thanks the Manchot Foundation for a doctoral scholarship.

The authors declare no competing financial interest.

Supplementary Material

pc4c00038_si_001.pdf (2.5MB, pdf)
pc4c00038_si_002.cif (5.9MB, cif)

References

  1. Mori T. Chiroptical Properties of Symmetric Double, Triple, and Multiple Helicenes. Chem. Rev. 2021, 121, 2373–2412. 10.1021/acs.chemrev.0c01017. [DOI] [PubMed] [Google Scholar]
  2. Tsurusaki A.; Kamikawa K. Multiple Helicenes Featuring Synthetic Approaches and Molecular Structures. Chem. Lett. 2021, 50, 1913–1932. 10.1246/cl.210409. [DOI] [Google Scholar]
  3. Kato K.; Segawa Y.; Itami K. Symmetric Multiple Carbohelicenes. Synlett 2019, 30, 370–377. 10.1055/s-0037-1610283. [DOI] [Google Scholar]
  4. Li C.; Yang Y.; Miao Q. Recent Progress in Chemistry of Multiple Helicenes. Chem. Asian. J. 2018, 13, 884–894. 10.1002/asia.201800073. [DOI] [PubMed] [Google Scholar]
  5. Fujikawa T.; Segawa Y.; Itami K. Synthesis, Structures, and Properties of pi-Extended Double Helicene: A Combination of Planar and Nonplanar pi-Systems. J. Am. Chem. Soc. 2015, 137, 7763–7768. 10.1021/jacs.5b03118. [DOI] [PubMed] [Google Scholar]
  6. Hu Y.; Paterno G. M.; Wang X. Y.; Wang X. C.; Guizzardi M.; Chen Q.; Schollmeyer D.; Cao X. Y.; Cerullo G.; Scotognella F.; Müllen K.; Narita A. pi-Extended Pyrene-Fused Double [7]Carbohelicene as a Chiral Polycyclic Aromatic Hydrocarbon. J. Am. Chem. Soc. 2019, 141, 12797–12803. 10.1021/jacs.9b05610. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Shan L.; Liu D.; Li H.; Xu X.; Shan B.; Xu J. B.; Miao Q. Monolayer Field-Effect Transistors of Nonplanar Organic Semiconductors with Brickwork Arrangement. Adv. Mater. 2015, 27, 3418–3423. 10.1002/adma.201500149. [DOI] [PubMed] [Google Scholar]
  8. Gan F.; Zhang G.; Liang J.; Shen C.; Qiu H. pi-Extended Diaza[7]helicenes with Dual Negatively Curved Heptagons: Extensive Synthesis and Spontaneous Resolution into Strippable Homochiral Lamellae with Helical Symmetry. Angew. Chem., Int. Ed. 2024, 63, e202320076. 10.1002/anie.202320076. [DOI] [PubMed] [Google Scholar]
  9. Tan J.; Xu X.; Liu J.; Vasylevskyi S.; Lin Z.; Kabe R.; Zou Y.; Müllen K.; Narita A.; Hu Y. Synthesis of a pi-Extended Double [9]Helicene. Angew. Chem., Int. Ed. 2023, 62, e202218494. 10.1002/anie.202218494. [DOI] [PubMed] [Google Scholar]
  10. Yang Y.; da Costa R. C.; Fuchter M. J.; Campbell A. J. Circularly polarized light detection by a chiral organic semiconductor transistor. Nature Photon 2013, 7, 634–638. 10.1038/nphoton.2013.176. [DOI] [Google Scholar]
  11. Zhang L.; Song I.; Ahn J.; Han M.; Linares M.; Surin M.; Zhang H. J.; Oh J. H.; Lin J. pi-Extended perylene diimide double-heterohelicenes as ambipolar organic semiconductors for broadband circularly polarized light detection. Nat. Commun. 2021, 12, 142. 10.1038/s41467-020-20390-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Zhang D. W.; Li M.; Chen C. F. Recent advances in circularly polarized electroluminescence based on organic light-emitting diodes. Chem. Soc. Rev. 2020, 49, 1331–1343. 10.1039/C9CS00680J. [DOI] [PubMed] [Google Scholar]
  13. Liu Y.; Ma Z.; Wang Z.; Jiang W. Boosting Circularly Polarized Luminescence Performance by a Double pi-Helix and Heteroannulation. J. Am. Chem. Soc. 2022, 144, 11397–11404. 10.1021/jacs.2c04012. [DOI] [PubMed] [Google Scholar]
  14. Wu Y. F.; Zhang L.; Zhang Q. Y.; Xie S. Y.; Zheng L. S. Multiple [n]helicenes with various aromatic cores. Org. Chem. Front. 2022, 9, 4726–4743. 10.1039/D2QO00988A. [DOI] [Google Scholar]
  15. Hu Y.; Wang X. Y.; Peng P. X.; Wang X. C.; Cao X. Y.; Feng X.; Müllen K.; Narita A. Benzo-Fused Double [7]Carbohelicene: Synthesis, Structures, and Physicochemical Properties. Angew. Chem., Int. Ed. 2017, 56, 3374–3378. 10.1002/anie.201610434. [DOI] [PubMed] [Google Scholar]
  16. Luo J.; Xu X.; Mao R.; Miao Q. Curved polycyclic aromatic molecules that are pi-isoelectronic to hexabenzocoronene. J. Am. Chem. Soc. 2012, 134, 13796–13803. 10.1021/ja3054354. [DOI] [PubMed] [Google Scholar]
  17. Barnett L.; Ho D. M.; Baldridge K. K.; Pascal R. A. The Structure of Hexabenzotriphenylene and the Problem of Overcrowded “D3h” Polycyclic Aromatic Compounds. J. Am. Chem. Soc. 1999, 121, 727–733. 10.1021/ja983471i. [DOI] [Google Scholar]
  18. Peña D.; Pérez D.; Guitián E.; Castedo L. Synthesis of Hexabenzotriphenylene and Other Strained Polycyclic Aromatic Hydrocarbons by Palladium-Catalyzed Cyclotrimerization of Arynes. Org. Lett. 1999, 1, 1555–1557. 10.1021/ol990864t. [DOI] [Google Scholar]
  19. Pradhan A.; Dechambenoit P.; Bock H.; Durola F. Highly Twisted Arenes by Scholl Cyclizations with Unexpected Regioselectivity. Angew. Chem., Int. Ed. 2011, 50, 12582–12585. 10.1002/anie.201105105. [DOI] [PubMed] [Google Scholar]
  20. Saito H.; Uchida A.; Watanabe S. Synthesis of a Three-Bladed Propeller-Shaped Triple [5]Helicene. J. Org. Chem. 2017, 82, 5663–5668. 10.1021/acs.joc.7b00486. [DOI] [PubMed] [Google Scholar]
  21. Hosokawa T.; Takahashi Y.; Matsushima T.; Watanabe S.; Kikkawa S.; Azumaya I.; Tsurusaki A.; Kamikawa K. Synthesis, Structures, and Properties of Hexapole Helicenes: Assembling Six [5]Helicene Substructures into Highly Twisted Aromatic Systems. J. Am. Chem. Soc. 2017, 139, 18512–18521. 10.1021/jacs.7b07113. [DOI] [PubMed] [Google Scholar]
  22. Berezhnaia V.; Roy M.; Vanthuyne N.; Villa M.; Naubron J.-V.; Rodriguez J.; Coquerel Y.; Gingras M. Chiral Nanographene Propeller Embedding Six Enantiomerically Stable [5]Helicene Units. J. Am. Chem. Soc. 2017, 139, 18508–18511. 10.1021/jacs.7b07622. [DOI] [PubMed] [Google Scholar]
  23. Roy M.; Berezhnaia V.; Villa M.; Vanthuyne N.; Giorgi M.; Naubron J. V.; Poyer S.; Monnier V.; Charles L.; Carissan Y.; Hagebaum-Reignier D.; Rodriguez J.; Gingras M.; Coquerel Y. Stereoselective Syntheses, Structures, and Properties of Extremely Distorted Chiral Nanographenes Embedding Hextuple Helicenes. Angew. Chem., Int. Ed. 2020, 59, 3264–3271. 10.1002/anie.201913200. [DOI] [PubMed] [Google Scholar]
  24. Zhang F.; Michail E.; Saal F.; Krause A. M.; Ravat P. Stereospecific Synthesis and Photophysical Properties of Propeller-Shaped C(90) H(48) PAH. Chem.—Eur. J. 2019, 25, 16241–16245. 10.1002/chem.201904962. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Artigas A.; Rigoulet F.; Giorgi M.; Hagebaum-Reignier D.; Carissan Y.; Coquerel Y. Overcrowded Triply Fused Carbo[7]helicene. J. Am. Chem. Soc. 2023, 145, 15084–15087. 10.1021/jacs.3c05415. [DOI] [PubMed] [Google Scholar]
  26. Fujikawa T.; Segawa Y.; Itami K. Synthesis and Structural Features of Quadruple Helicenes: Highly Distorted pi Systems Enabled by Accumulation of Helical Repulsions. J. Am. Chem. Soc. 2016, 138, 3587–3595. 10.1021/jacs.6b01303. [DOI] [PubMed] [Google Scholar]
  27. Tanaka H.; Ikenosako M.; Kato Y.; Fujiki M.; Inoue Y.; Mori T. Symmetry-based rational design for boosting chiroptical responses. Commun. Chem. 2018, 1, 38. 10.1038/s42004-018-0035-x. [DOI] [Google Scholar]
  28. Kashihara H.; Asada T.; Kamikawa K. Synthesis of a Double Helicene by a Palladium-Catalyzed Cross-Coupling Reaction: Structure and Physical Properties. Chem.—Eur. J. 2015, 21, 6523–6527. 10.1002/chem.201500074. [DOI] [PubMed] [Google Scholar]
  29. Fujikawa T.; Mitoma N.; Wakamiya A.; Saeki A.; Segawa Y.; Itami K. Synthesis, properties, and crystal structures of pi-extended double [6]helicenes: contorted multi-dimensional stacking lattice. Org. Biomol. Chem. 2017, 15, 4697–4703. 10.1039/C7OB00987A. [DOI] [PubMed] [Google Scholar]
  30. Kato K.; Segawa Y.; Scott L. T.; Itami K. A Quintuple [6]Helicene with a Corannulene Core as a C(5) -Symmetric Propeller-Shaped pi-System. Angew. Chem., Int. Ed. 2018, 57, 1337–1341. 10.1002/anie.201711985. [DOI] [PubMed] [Google Scholar]
  31. Lin H. A.; Kato K.; Segawa Y.; Scott L. T.; Itami K. Synthesis and structural features of thiophene-fused analogues of warped nanographene and quintuple helicene. Chem. Sci. 2019, 10, 2326–2330. 10.1039/C8SC04470H. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Kise K.; Ooi S.; Saito H.; Yorimitsu H.; Osuka A.; Tanaka T. Five-Fold Symmetric Pentaindolo- and Pentakis(benzoindolo)Corannulenes: Unique Structural Dynamics Derived from the Combination of Helical and Bowl Inversions. Angew. Chem., Int. Ed. 2022, 61, e202112589. 10.1002/anie.202112589. [DOI] [PubMed] [Google Scholar]
  33. Meng D.; Liu G.; Xiao C.; Shi Y.; Zhang L.; Jiang L.; Baldridge K. K.; Li Y.; Siegel J. S.; Wang Z. Corannurylene Pentapetalae. J. Am. Chem. Soc. 2019, 141, 5402–5408. 10.1021/jacs.9b00053. [DOI] [PubMed] [Google Scholar]
  34. Wu Y. F.; Ying S. W.; Su L. Y.; Du J. J.; Zhang L.; Chen B. W.; Tian H. R.; Xu H.; Zhang M. L.; Yan X.; Zhang Q.; Xie S. Y.; Zheng L. S. Nitrogen-Embedded Quintuple [7]Helicene: A Helicene-Azacorannulene Hybrid with Strong Near-Infrared Fluorescence. J. Am. Chem. Soc. 2022, 144, 10736–10742. 10.1021/jacs.2c00794. [DOI] [PubMed] [Google Scholar]
  35. Wu Y. F.; Ying S. W.; Liao S. D.; Zhang L.; Du J. J.; Chen B. W.; Tian H. R.; Xie F. F.; Xu H.; Deng S. L.; Zhang Q.; Xie S. Y.; Zheng L. S. Sulfur-Doped Quintuple [9]Helicene with Azacorannulene as Core. Angew. Chem., Int. Ed. 2022, 61, e202204334. 10.1002/anie.202204334. [DOI] [PubMed] [Google Scholar]
  36. Zhu Y.; Wang J. Helical Synthetic Nanographenes with Atomic Precision. Acc. Chem. Res. 2023, 56, 363–373. 10.1021/acs.accounts.2c00767. [DOI] [PubMed] [Google Scholar]
  37. Zhu Y.; Xia Z.; Cai Z.; Yuan Z.; Jiang N.; Li T.; Wang Y.; Guo X.; Li Z.; Ma S.; Zhong D.; Li Y.; Wang J. Synthesis and Characterization of Hexapole [7]Helicene, A Circularly Twisted Chiral Nanographene. J. Am. Chem. Soc. 2018, 140, 4222–4226. 10.1021/jacs.8b01447. [DOI] [PubMed] [Google Scholar]
  38. Guo X.; Yuan Z.; Zhu Y.; Li Z.; Huang R.; Xia Z.; Zhang W.; Li Y.; Wang J. A Nitrogen-Doped Hexapole [7]Helicene versus Its All-Carbon Analogue. Angew. Chem., Int. Ed. 2019, 58, 16966–16972. 10.1002/anie.201907972. [DOI] [PubMed] [Google Scholar]
  39. Wang Y.; Yin Z.; Zhu Y.; Gu J.; Li Y.; Wang J. Hexapole [9]Helicene. Angew. Chem., Int. Ed. 2019, 58, 587–591. 10.1002/anie.201811706. [DOI] [PubMed] [Google Scholar]
  40. Pun S. H.; Cheung K. M.; Yang D.; Chen H.; Wang Y.; Kershaw S. V.; Miao Q. A Near-Infrared Absorbing and Emissive Quadruple Helicene Enabled by the Scholl Reaction of Perylene. Angew. Chem., Int. Ed. 2022, 61, e202113203. 10.1002/anie.202113203. [DOI] [PubMed] [Google Scholar]
  41. Li J. K.; Chen X. Y.; Zhao W. L.; Guo Y. L.; Zhang Y.; Wang X. C.; Sue A. C.; Cao X. Y.; Li M.; Chen C. F.; Wang X. Y. Synthesis of Highly Luminescent Chiral Nanographene. Angew. Chem., Int. Ed. 2023, 62, e202215367. 10.1002/anie.202215367. [DOI] [PubMed] [Google Scholar]
  42. Zhu Y.; Guo X.; Li Y.; Wang J. Fusing of Seven HBCs toward a Green Nanographene Propeller. J. Am. Chem. Soc. 2019, 141, 5511–5517. 10.1021/jacs.9b01266. [DOI] [PubMed] [Google Scholar]
  43. Figueira-Duarte T. M.; Müllen K. Pyrene-based materials for organic electronics. Chem. Rev. 2011, 111, 7260–7314. 10.1021/cr100428a. [DOI] [PubMed] [Google Scholar]
  44. Figueira-Duarte T. M.; Del Rosso P. G.; Trattnig R.; Sax S.; List E. J.; Müllen K. Designed suppression of aggregation in polypyrene: toward high-performance blue-light-emitting diodes. Adv. Mater. 2010, 22, 990–993. 10.1002/adma.200902744. [DOI] [PubMed] [Google Scholar]
  45. Ozaki K.; Kawasumi K.; Shibata M.; Ito H.; Itami K. One-shot K-region-selective annulative pi-extension for nanographene synthesis and functionalization. Nat. Commun. 2015, 6, 6251. 10.1038/ncomms7251. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Li Y.; Jia Z.; Xiao S.; Liu H.; Li Y. A method for controlling the synthesis of stable twisted two-dimensional conjugated molecules. Nat. Commun. 2016, 7, 11637. 10.1038/ncomms11637. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Kumar B.; Strasser C. E.; King B. T. t-Butyl biphenylation of o-dibromoarenes: a route to soluble polycyclic aromatic hydrocarbons. J. Org. Chem. 2012, 77, 311–316. 10.1021/jo2019587. [DOI] [PubMed] [Google Scholar]
  48. Ito H.; Ozaki K.; Itami K. Annulative pi-Extension (APEX): Rapid Access to Fused Arenes, Heteroarenes, and Nanographenes. Angew. Chem., Int. Ed. 2017, 56, 11144–11164. 10.1002/anie.201701058. [DOI] [PubMed] [Google Scholar]
  49. Coventry D. N.; Batsanov A. S.; Goeta A. E.; Howard J. A.; Marder T. B.; Perutz R. N. Selective Ir-catalysed borylation of polycyclic aromatic hydrocarbons: structures of naphthalene-2,6-bis(boronate), pyrene-2,7-bis(boronate) and perylene-2,5,8,11-tetra(boronate) esters. Chem. Commun. 2005, 2172–2174. 10.1039/b501778e. [DOI] [PubMed] [Google Scholar]
  50. Corey J. Y.; Chang L. S. New Precursors to Silafluorenes. J. Organomet. Chem. 1986, 307, 7–14. 10.1016/0022-328X(86)80170-X. [DOI] [Google Scholar]
  51. King B. T.; Kroulik J.; Robertson C. R.; Rempala P.; Hilton C. L.; Korinek J. D.; Gortari L. M. Controlling the Scholl reaction. J. Org. Chem. 2007, 72, 2279–2288. 10.1021/jo061515x. [DOI] [PubMed] [Google Scholar]
  52. Zhang Y.; Pun S. H.; Miao Q. The Scholl Reaction as a Powerful Tool for Synthesis of Curved Polycyclic Aromatics. Chem. Rev. 2022, 122, 14554–14593. 10.1021/acs.chemrev.2c00186. [DOI] [PubMed] [Google Scholar]
  53. Zhai L.; Shukla R.; Rathore R. Oxidative C-C bond formation (Scholl reaction) with DDQ as an efficient and easily recyclable oxidant. Org. Lett. 2009, 11, 3474–3477. 10.1021/ol901331p. [DOI] [PubMed] [Google Scholar]
  54. Shen C.; Zhang G.; Ding Y.; Yang N.; Gan F.; Crassous J.; Qiu H. Oxidative cyclo-rearrangement of helicenes into chiral nanographenes. Nat. Commun. 2021, 12, 2786. 10.1038/s41467-021-22992-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Pun S. H.; Wen E. C. H.; Xia Z.; Chen H.; Fischer F. R.; Miao Q. Reactivity, Regioselectivity, and Synthetic Application of 2-Pyrenyl Units in Scholl Reactions. CCS Chem. 2023, 5, 2069–2077. 10.31635/ccschem.023.202302970. [DOI] [Google Scholar]
  56. Pun S. H.; Wang Y.; Chu M.; Chan C. K.; Li Y.; Liu Z.; Miao Q. Synthesis, Structures, and Properties of Heptabenzo[7]circulene and Octabenzo[8]circulene. J. Am. Chem. Soc. 2019, 141, 9680–9686. 10.1021/jacs.9b03910. [DOI] [PubMed] [Google Scholar]
  57. Huang H. C.; Hsieh Y. C.; Lee P. L.; Lin C. C.; Ho Y. S.; Shao W. K.; Hsieh C. T.; Cheng M. J.; Wu Y. T. Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties. J. Am. Chem. Soc. 2023, 145, 10304–10313. 10.1021/jacs.3c01647. [DOI] [PubMed] [Google Scholar]
  58. Liu T.; Yang J.; Geyer F.; Conrad-Burton F. S.; Hernandez Sanchez R.; Li H.; Zhu X.; Nuckolls C. P.; Steigerwald M. L.; Xiao S. Stringing the Perylene Diimide Bow. Angew. Chem., Int. Ed. 2020, 59, 14303–14307. 10.1002/anie.202004989. [DOI] [PubMed] [Google Scholar]
  59. Cardona C. M.; Li W.; Kaifer A. E.; Stockdale D.; Bazan G. C. Electrochemical considerations for determining absolute frontier orbital energy levels of conjugated polymers for solar cell applications. Adv. Mater. 2011, 23, 2367–2371. 10.1002/adma.201004554. [DOI] [PubMed] [Google Scholar]
  60. Nakai Y.; Mori T.; Inoue Y. Theoretical and experimental studies on circular dichroism of carbo[n]helicenes. J. Phys. Chem. A 2012, 116, 7372–7385. 10.1021/jp304576g. [DOI] [PubMed] [Google Scholar]

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