Contorted Heteroannulated Tetraareno[a,d,j,m]coronenes

Abstract

Fused polycyclic aromatic compounds are interesting materials for organic electronics applications. To fine‐tune photophysical or electrochemical properties, either various substituents can be attached or heteroatoms (such as N or S) can be incorporated into the fused aromatic backbone. Coronenes and heterocoronenes are promising compounds in this respect. Up until now, the possibilities for varying the attached fused heteroaromatics at the coronene core were quite limited, and realizing both electron‐withdrawing and ‐donating rings at the same time was very difficult. Here, a series of pyridine, anisole and thiophene annulated tetraareno[a,d,j,m]coronenes has been synthesized by a facile two‐step route that is a combination of Suzuki‐Miyaura cross‐coupling and a following cyclization step, starting from three different diarenoperylene dibromides. The contorted molecular π‐planes of the obtained cata‐condensed tetraarenocoronenes were analyzed by single‐crystal X‐ray crystallography, and the photophysical and electrochemical properties were systematically investigated by UV/Vis spectroscopy and cyclovoltammetry.

Tuning tetraarenocoronenes: Cata‐condensed heteroannulated tetraarenocoronenes with C _2h symmetry have been obtained from three doubly brominated diarenoperylenes. X‐ray diffraction showed that the coronenes mostly adopt S‐shaped contorted π‐planes. The large variety of fused rings in the coronenes′ core allows good control of their photophysical properties and thus their potential use in organic electronics applications.

Introduction

Coronene or [6]circulene, in which one benzene ring is fully surrounded by another six fused hexagonal benzenoid rings, is an often found subunit of polycyclic aromatic hydrocarbons (PAHs). ^[1] Since its first synthesis by Clar and co‐workers in 1957, ^[2] fused aromatic compounds based on coronene have been intensively investigated by synthetic organic chemists and material scientists. ^[3] The strain‐free nature makes the π‐framework of coronene an ideal planar structure. ^[4] Further π‐extensions of coronene by peri‐condensation does not change the planarity of the central π‐plane, ^[5] whereas multifold cata‐condensation introduces contortion to the π‐framework, because of the steric congestion caused by the generation of six cove regions at the peripheries. ^[6] Cata‐condensed hexabenzocoronene (c‐HBC) and its derivatives serve as representative examples in which the six benzene rings at the periphery displace above or below the molecular π‐surface alternatingly as a result of the six cove regions.[ ^3f , ⁷ ] In comparison to their planar counterparts, contorted PAHs show increased solubilities due to reduced intermolecular aggregations, which open the possibilities to use these compounds for solution‐processed applications. ^[8] Furthermore, due to the tendency to pack co‐facially through self‐complementary interactions, larger intermolecular electronic coupling and thus higher charge transport rate along the π‐stacking direction in contorted coronene‐based PAHs are expected. All these features make contorted PAHs good candidates for organic electronics.[ ^7b , ⁹ ]

In order to fine‐tune the spectroscopic and electronic properties, heteroatoms such as nitrogen, ^[10] sulfur,[ ^8f , ^8h , ⁸ⁱ , ^9d , ¹¹ ] oxygen, ^[12] boron ^[13] or both boron and nitrogen ^[14] are incorporated into the backbone of coronene‐based PAHs. Therefore, facile synthetic methods have been developed in recent years to obtain structurally defined heteroannulated coronenes.[ ^3d , ^3e , ¹⁵ ] For instance reported Nuckolls and co‐workers the synthesis of dibenzotetrathienocoronene and its derivatives in 2011, ^[8f] which starts with the PPh₃‐mediated Ramirez reaction of 6,13‐pentacenequinone with CBr₄ to give the 1,1,8,8‐tetrabromobisolefin that was used in Suzuki‐Miyaura cross‐coupling reaction with thiophene boronic ester followed by Mallory photocyclization, to give D _2h‐symmetric dibenzotetra‐thienocoronenes in 47–90 % overall yield. Another strategy to obtain cata‐condensed tribenzotrithienocoronenes was reported by Wei and co‐workers; it starts with the Suzuki‐Miyaura cross‐coupling reaction of 1,3,5‐tri(bromomethyl)‐benzene and substituted phenyl boronic acids to give 1,3,5‐tribenzylbenzenes. ^[16] The key‐step towards C _3h‐symmetric tribenzotrithienocoronenes was a tandem Friedel‐Crafts alkylation/intramolecular cyclodehydrogenation between the 1,3,5‐tribenzylbenzenes and thiophene‐3‐carbaldehyde using FeCl₃ as the oxidant/Lewis acid and acetic anhydride as the dehydrating agent in a CH₂Cl₂/CH₃NO₂ mixture. Some time ago, Müllen and co‐workers reported the synthesis of a three‐fold quinoxalino‐fused coronene based on a hexamethoxy [2.2.2]‐paracyclophane. ^[17] The macrocycle was converted to hexa‐methoxycoronene by photocyclization. Demethylation and oxidative workup gave the coronene quinone, which was reacted with o‐phenylenediamine via condensation to give the final product with D _3h symmetry, using a similar strategy as reported by Zinke and co‐workers. ^[18]

Our research group has been focusing on developing new facile synthetic methods to complex aromatic π‐systems by different approaches. ^[19] In 2016, a series of cata‐condensed diarenoperylenes were reported based on a new synthetic route in which two additional aromatic rings are peri‐fused to the pentacene framework by condensation of an ortho‐aldehyde unit. ^[20] The diarenoperylenes were then regioselectively two‐fold brominated, enabling the synthesis of thiophene‐fused tetraareno[a,d,j,m]coronenes by palladium‐catalyzed Suzuki‐Miyaura cross‐coupling reactions with thienyl boronic ester and subsequent photocyclization (Scheme 1). ^[21] In contrast to the aforementioned approaches, this one allows cata‐condensed tetraarenocoronenes of lower symmetry (C _2h, without consideration of the contortion of the π‐planes) to be synthesized with different fused rings (electron‐withdrawing or ‐donating), which is presented herein.

Scheme 1.

Synthesis of thiophene‐fused tetraarenocoronenes 5, 6 and 9. ^[21] a) (5‐hexylthiophen‐3‐yl)boronic acid pinacol ester, 5 mol% Pd₂(dba)₃, 7.5 mol% tBu₃PHBF₄, 2 M K₂CO₃ (aq.), THF, 80 °C, 16 h; b) hν, I₂, propylene oxide, cyclohexane, 4 h. dba: dibenzylideneacetone, THF: tetrahydrofuran.

Results and Discussion

Synthesis

According to the reactions of dibromoperylenes 1,2 and 7 with (5‐hexylthiophen‐3‐yl) boronic ester as has been prior described (Scheme 1), ^[21] these were cross‐coupled with boronic ester 10 or 15 (Scheme 2) to give the corresponding cross‐coupling products in yields between 36 % (20) and 91 % (17). It is worth mentioning that the two methoxy groups at the pyridine ring of 15 are necessary for the successful cross‐coupling reactions, as no conversion was observed when 1, 2 or 7 were treated with 3‐pyridylboronic acid instead under the same conditions, in which the transmetalation process might be suppressed by the electron‐poor nature of the unsubstituted pyridyl boronic acid. ^[22]

Scheme 2.

Synthesis of cata‐condensed tetraareno[a,d,j,m]coronenes 13, 14, 18, 19, 21 and 23. a) 5 mol% Pd₂(dba)₃, 7.5 mol% tBu₃PHBF₄, 2 M K₂CO₃ (aq.), THF, 80 °C, 16 h; b) hν, I₂, propylene oxide, cyclohexane, 4–24 h; c) DDQ, TfOH, CH₂Cl₂, 0 °C, 20 min. DDQ: 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone, TfOH: trifluoromethanesulfonic acid.

The next steps are the cyclizations of the cross‐coupling products 11, 12, 16, 17, 20 and 22 to the tetraarenocoronenes 13, 14, 18, 19, 21 and 23. First, the photoreactions under the conditions similar to those used for the conversion of 3, 4 and 8 to the thiophene‐fused coronenes 5, 6 and 9 were applied. ^[21] By this method, pyridine‐substituted compounds 16 and 22 were photocyclized to 18 and 23 in 70 and 73 % yields, respectively. However, in the series with the bismethoxy‐pyridyl units, least electron‐rich compound 17 is an exception, as only 26 % of the fully cyclized product 19 was collected after irradiation for 16 h in the presence of 4.0 equiv. of I₂. The poor solubility of substrate 17 in cyclohexane (<0.5 μM) is responsible for the low yield, as only a small portion of the aggregated substrate particles were consumed during the reaction. Photocyclizations of 3‐hexyloxyphenyl substituted compounds 11, 12 and 20 gave even much lower yields in the photocyclization reactions and only 18 % yield of 13 and 3 % of 14 were isolated. Even no cata‐condensed coronene 21 was formed after irradiating substrate 20 for 24 h in the presence of 4.0 equiv. of I₂ and excess propylene oxide.

In comparison to photocyclization reactions, intramolecular oxidative cyclodehydrogenation (Scholl reaction) is a more widely used approach to make fused PAHs by a ring‐closing step. ^[23] Therefore, the three hexyloxyphenyl substituted compounds 11, 12 and 20, were subject to Scholl‐type reactions using DDQ along with triflic acid (Scheme 2). The isolated yield of tetrabenzocoronene 13 was increased from 18 % to 45 % with part of the product lost as the phenol species. ^[24] It should be emphasized that the attached electron‐donating 3‐hexyloxy group plays a crucial role in the cyclization process, as it was found that the oxidative cyclodehydrogenation undergoes double pentannulation if there is no substituent present on the free phenyl rings. ^[19e] The Scholl reaction also makes the cyclization of 20 to the dithiophene‐based compound 21 possible. Treating compound 20 with 6 equiv. of DDQ in the presence of triflic acid in CH₂Cl₂ gave the doubly cyclized product 21 in 62 % yield. Unfortunately, any attempts to increase the transformation of pyridine based 12 to 14 by Scholl‐type conditions failed and gave only decomposition products.

Single‐crystal X‐ray structure analysis

High‐quality single crystals of compound 13, 14, 21 and 23 suitable for X‐ray crystallography analysis were obtained by slow vapor diffusion of CH₃OH into the sample solution in CHCl₃ or CH₂Cl₂.

Isosteric coronenes 13 and 14 show similar conformations and crystalline packing motifs. Both compounds crystallize in the triclinic space group P‐1, with the molecules sitting on inversion centers. Besides the two cove regions, there is also steric repulsion between the fused hexyloxyphenyl rings and the bulky tert‐butyl groups in both structures 13 and 14, which make the two coronenes more contorted than the prior reported thiophene‐based molecules 5, 6 and 9. ^[21] This is reflected by the dihedral angles of 27.2–28.0° of the four carbon atoms in the bay regions where the tert‐butyl groups are attached (Figure 1a and b) being larger than those of 5, 6 and 9 at the same positions (14.4–26.0°) ^[21] and that the angles between ring e at the periphery and the central ring a (28.2° for 13 and 28.4° for 14, Figure 1d and e) are larger than those of the thiophene‐fused congeners 5, 6 and 9 (21.2–26.0°). Both structures show offset coplanar arrangements of the molecules (Figure 1g and h), which do not show any intermolecular π‐stacking, but mainly pack through dispersion interactions.

Figure 1.

X‐ray crystal structures of coronenes 13 (a, d, g and j), 14 (b, e, h and k) and 23 (c, f, i and l). ORTEP plots are at 50 % probability. Enclathrated solvent molecules and hydrogen atoms (except in j–l) are omitted for clarity. The hexyloxy chains in a, b, d, e, g and h are replaced by methoxy groups. Colors for heteroatoms: blue=nitrogen, yellow=sulfur, red=oxygen. For detailed crystallographic data, see the Supporting Information.

Coronene 23 with both cata‐condensed thiophene and pyridine rings, crystallizing in the monoclinic space group P2₁/n, shows a less twisted π‐plane than 13 or 14. The angle between the dimethoxypyridine ring e and the central ring a is 23.8° (Figure 1f). Again, no pronounced intermolecular π‐stacking is observed, but molecules pack mainly via non‐directional dispersion interactions. One molecule perpendicular to the crystalline lattice is surrounded by four parallel molecular dimers (Figure 1i).

Dibenzodithienocoronene 21 crystallizes in the cubic space group Fdd2 (Figure 2). It is interesting that the molecular contortion of 21 is different in conformation from all other coronenes described herein and published before. ^[21] In 21 two annulated hexyloxy‐benzene rings bend towards the same side (U‐shape) while the two fused thiophene rings bend towards the opposite side (S‐shape) of the molecular π‐plane, whereas in all other compounds it is exclusively S‐shape conformations that are found. The bending deformation (the angle between the two hexyloxy chain attached benzene rings) is 56.4° (Figure 2b). Due to the negative curvature,[ ^4b , ²⁵ ] 21 shows chirality and was found as a racemic crystal with two enantiomers. Two molecules sharing the same chirality (M,M or P,P) form one π‐dimer (Figure 2c). In contrast to all other tetraarenocoronenes, here a distinct π‐stacking distance with d _π–π=3.25 Å is observed (Figure 2d).

Figure 2.

X‐ray crystal structures of coronene 21. ORTEP plots are at 50 % probability. Enclathrated solvent molecules, hydrogen atoms (in a–c) and the tert‐butyl groups (in d) are omitted for clarity. The hexyloxy chains are replaced by methoxy groups in a and b and omitted in d. The two enantiomers are highlighted in different colors in c. (M,M: green and P,P: blue). Colors as in Figure 1. For detailed crystallographic data, see the Supporting Information.

By temperature‐dependent ¹H NMR spectroscopy the inter‐conversion energy of two enantiomers of coronene 21 was determined to be 41.5 kJ mol⁻¹ (90.2 Hz) with a coalescence temperature of about −70 °C, observed with the splitting of the two signals of the −OCH₂ groups of the hexyloxy chains at 4.31 ppm (Figure 3).

Figure 3.

Variable‐temperature ¹H NMR spectra (300 MHz, CD₂Cl₂) of coronene 21. For full spectra, see the Supporting Information.

Spectroscopic and electrochemical properties

All precursors and the cata‐condensed tetraarenocoronenes were investigated by photophysical and electrochemical characterizations (Figure 4 and Table 1) performed in CH₂Cl₂ at room temperature. For the sake of completeness, the data of compounds 3–6, 8 and 9 will be included in this comparative discussion. Well‐resolved β‐ and p‐band (π–π* transitions) absorptions ^[26] are observed in the UV/Vis spectra of all compounds. For the uncyclized precursors the positions of absorption maxima depend mainly on the diarenoperylene backbones. For example, compounds 8, 20 and 22 with the same thiophene‐fused perylene backbone, show similar p‐band absorption maxima at 477–478 nm. This absorption peak shows a significantly hypsochromic shift to 433 nm for the pyridine‐fused compound 12. A similar phenomenon is also found for the corresponding emission spectra. Compounds 3, 4, 11, 12, 16 and 17 emit at 472–481 nm, while the emission maxima of the thiophene‐fused compounds 8, 20 and 22 shift bathochromically to 529–533 nm.

Figure 4.

UV/Vis absorption (solid lines) and photoluminescence (dotted lines) spectra of the uncyclized precursors (black lines) and the corresponding tetraarenocoronenes (red lines) measured in CH₂Cl₂ (c=4—26 μmol L⁻¹) at room temperature. The results of compounds 3, 4 and 8 and 5, 6 and 9 are taken from ref. [21].

Table 1.

Summary of the photophysical and electrochemical characterizations of uncyclized precursors and cata‐condensed coronenes.

Compd	λ abs [nm][a,b]	λ em (λ ex) [nm][a]	Φ [%][a,d]	$\tilde{v}$ [cm−1][a,c]	$E\genfrac{}{}{0pt}{}{\mathrm{opt}}{\mathrm{g}}$ [eV][a,b]	IPCV [eV][e,f]	EACV [eV][g]	$E\genfrac{}{}{0pt}{}{\mathrm{CV}}{\mathrm{g}}$ [eV][h]	$E\genfrac{}{}{0pt}{}{\mathrm{DFT}}{\mathrm{HOMO}}$ [eV][i]	$E\genfrac{}{}{0pt}{}{\mathrm{DFT}}{\mathrm{LUMO}}$ [eV][i]
3 [j]	302, 312, 416, 432	479, 502 (416)	14.1±1	2271	2.7	−5.2	−2.5	2.7	−5.1	−2.0
4 [j]	307, 317, 421, 435	481, 502 (421)	12.4±0.4	2198	2.7	−5.3	−2.7	2.7	−5.2	−2.1
8 [j]	298, 454, 478	531 (310)	37.7±0.1	2088	2.4	−5.0	−2.6	2.4	−4.8	−1.9
11	299, 311, 341, 411, 431	472, 502 (311)	53.5±1.3	2015	2.7	−5.2	−2.5	2.7	−5.1	−2.0
12	293, 305, 317, 414, 433	475, 500 (414)	55.3±0.7	2042	2.7	−5.4	−2.6	2.8	−5.2	−2.1
16	302, 311, 647, 416, 435	478, 501 (311)	58.4±0.6	2068	2.7	−5.3	−2.6	2.7	−5.2	−2.1
17	306, 341, 357, 418, 436	478, 506 (341)	54.4±2.0	2015	2.7	−5.3	−2.6	2.7	−5.3	−2.2
20	298, 452, 474	529 (452)	76.3±2.3	2193	2.4	−5.0	−2.6	2.4	−4.8	−1.9
22	300, 376, 456, 478	533 (478)	77.5±1.0	2156	2.4	−5.1	−2.6	2.5	−4.9	−2.0
5 [j]	296, 349, 363, 409, 433	482, 512 (363)	2.5±0.1	2348	2.7	−5.2	−2.5	2.7	−5.1	−1.9
6 [j]	284, 350, 364, 413, 436	476, 509 (364)	2.7±0.1	1927	2.7	−5.3	−2.6	2.7	−5.3	−2.1
9 [j]	350, 363, 398, 419, 442	480, 509 (363)	6.8±0.1	1791	2.7	−5.1	−2.5[k]	n. d.	−5.1	−1.8
13	355, 373, 399, 422, 447	485, 517 (373)	15.0±0.4	1753	2.7	−5.2	−2.6	2.6	−5.1	−2.1
14	355, 373, 421, 446, 475	479, 512 (355)	21.9±0.6	1545	2.5	−5.4	−2.6	2.8	−5.2	−2.2
18	354, 367, 414, 436, 481	486, 519 (367)	35.0±0.4	2360	2.5	−5.3	−3.0	2.3	−5.1	−2.0
19	357, 367, 424, 439, 475	480, 513 (367)	23.1±1.2	1946	2.5	−5.4	−3.3	2.1	−5.3	−2.1
21	352, 368, 447, 454, 484	491, 524 (368)	17.5±0.5	2005	2.5	−5.0	−2.6	2.4	−4.9	−1.9
23	368, 415, 438, 479	482, 515 (368)	16.4±0.8	2084	2.5	−5.2	−2.5	2.6	−5.1	−2.0

[a] Measured in CH₂Cl₂ at room temperature. [b] Estimated from absorption onset. [c] Stokes's shift. [d] Fluorescence quantum yield. [e] Ionization potential. [f] Measured in 0.1 M nBu₄NClO₄ in CH₂Cl₂ at room temperature. The scan speed was 100 mV s⁻¹, and ferrocene/ferrocenium (Fc/Fc⁺) was used as internal reference. IP^CV=−($E\genfrac{}{}{0pt}{}{\mathrm{ox}}{\mathrm{onset}}$ +4.8 eV). EA^CV=−($E\genfrac{}{}{0pt}{}{\mathrm{red}}{\mathrm{onset}}$ +4.8 eV). [g] Electron affinity. [h] $E\genfrac{}{}{0pt}{}{\mathrm{CV}}{\mathrm{g}}$ =EA^CV−IP^CV. [i] Calculated by DFT in vacuum using Spartan 14 at the B3LYP/6‐311G* level of theory. [j] Data taken from reference. ^[21] [k] EA^CV=IP^CV+$E\genfrac{}{}{0pt}{}{\mathrm{opt}}{\mathrm{g}}$ .

The sharp β‐band absorptions in the range of 350–370 nm with significantly increased extinction coefficients are observed in the UV/Vis absorption spectra of all tetraarenocoronenes, clearly indicating the formation of the coronene central cores by cyclodehydrogenation.[ ⁶ , ²⁷ ] Absorption spectra predicted by the time‐dependent density functional theory (TDDFT) calculations indicate that these strong β‐band absorptions in the region of 345–381 nm origin from three main transitions (HOMO‐1→LUMO+1, HOMO‐1→LUMO and HOMO→LUMO+1) with large oscillator strengths (Figure S107–S115 and Table S5–S14). The highest extinction coefficients (>1.60×10⁵ M⁻¹ cm⁻¹) are observed for coronenes 5, 6 and 9 with annulated hexylthiophene rings. Tetrabenzocoronene 13 without any heteroatoms in the aromatic backbone shows two β‐band absorption peaks at 355 and 373 nm, along with one shoulder at 344 nm. Furthermore, two p‐band absorption peaks at 422 and 447 nm were observed, with a high extinction coefficient of 3.68×10⁴ M⁻¹ cm⁻¹ at 447 nm. Note that 13 shows the most bathochromic shift in the p‐band absorption in comparison to other pyridine or thiophene annulated coronenes. In the cases of double thiophene and double pyridine fused coronenes (6 and 23), the β‐band absorptions get sharper with only one maximum at 364 and 368 nm, respectively, while the corresponding extinction coefficients increase in comparison to the tetrabenzocoronene 13. Tetrakispyridinocoronene 19 shows moderate intensities for both of the β‐ and the p‐bands. For coronene 9 with four thiophene units a sharp β‐band absorption peak at 363 nm with the highest extinction coefficient of 1.75×10⁵ M⁻¹ cm⁻¹ in this series is detected. One characteristic absorption peak at 398 nm is observed for 9. ^[8h] Cata‐condensed coronenes with pyridine annulations (14, 18, 19, and 23, except 6) and negatively curved coronene 21 show α‐bands (n–π* transition) at around 480 nm, of which 21 has the most bathochromically shifted maximum at 484 nm.

Emission spectra with similar patterns are found in this coronene series. One main emission peak at 476–486 nm and one second shoulder peak at 509–524 nm are observed in all cases. Coronene 21 shows the most bathochromic emission at 491 and 524 nm. In comparison to the precursors before cyclization, the fluorescence quantum yields of all coronenes decrease, while coronenes with only nitrogen doping show moderate quantum yields of over 20 %.

By cyclovoltammetry the oxidation and reduction waves were measured reflecting the ionization potentials (IPs) and electron affinities (EAs) of all the precursors and the fused coronenes (Table 1 and the Supporting Information). For the tetrabenzocoronene 13, the IP and EA are determined to be at −5.2 and −2.6 eV, respectively. The IPs of the pyridine‐fused coronenes 6, 14, 18 and 19 are about 0.2 eV lower in energy than that of 13, and the tetrakispyridinocoronene 19 shows the most stabilized energy levels of IP=−5.4 and EA=−3.3 eV. Annulation with thiophene rings slightly increase the IPs, in the cases of thiophene‐fused molecules 5, 9 and 21.

DFT calculations

Structural optimizations of the nine tetraarenocoronenes in vacuum were performed based on density functional theory (DFT) calculations at the B3LYP/6‐311G* level of theory. ^[28] The calculated levels of frontier molecular orbitals (FMOs) are summarized in Table 1 and the FMOs are depicted in Figure 5. The FMOs of tetrabenzocoronene 13 were calculated to be at E _HOMO=−5.09 eV and E _LUMO=−2.09 eV. The HOMO levels are slightly stabilized by 0.03–0.04 eV while the LUMO levels are destabilized by 0.11–0.15 eV, if the cata‐condensed hexyloxy‐benzene rings are replaced by hexylthiophene (5) or dimethoxy‐pyridine rings (18). Both the HOMOs and LUMOs of the pyridine‐fused coronenes 6, 14 and 19 are stabilized in comparison to the congeners of 13, 5 and 18, respectively, because of the electron‐withdrawing nature of the pyridyl units. The substitution of benzene rings by hexylthiophene (6) or dimethoxypyridine rings (19) causes similar effects to the FMO levels compared to those of 5, 13 and 18, with the HOMOs getting slightly stabilized by 0.04 eV and the LUMOs destabilized by 0.07–0.09 eV. The highest HOMO level (−4.93 eV) and smallest HOMO‐LUMO gap (3.01 eV) in this coronene series is found for negatively curved molecule 21; this is consistent with the experimentally measured UV/Vis spectra and the electrochemical data. Therefore, the levels of FMOs of these nine cata‐condensed heteroannulated coronenes mainly depend on the aromatic rings fused to the [d,m] edges of the central coronene cores. The aromatic units fused to the [a,j] edges give slightly stabilized HOMOs and destabilized LUMOs.

Figure 5.

Calculated frontier molecular orbitals of the fused coronenes based on DFT at the B3LYP/6‐311G* level of theory using Spartan 14. Black lines: HOMO, red lines: LUMO. The results of compounds 5, 6 and 9 are taken from ref. [21]. The hexyl and hexyloxy chains were replaced by methyl or methoxy groups during the calculations for simplification.

Conclusions

Starting from three doubly brominated diarenoperylenes, cata‐condensed heteroannulated tetraareno[a,d,j,m]coronenes with C _2h symmetry (assuming that the central π‐planes are planar) were obtained by Suzuki‐Miyaura cross‐coupling and subsequent oxidative ring‐closure (Mallory photocyclization or Scholl reaction). By single‐crystal X‐ray diffraction it was found that the tetraareno[a,d,j,m]coronenes adopt S‐shaped contorted π‐planes due to the formation of two cove regions and the repulsion between the bulky tert‐butyl groups and the aromatic units at the [a,j] positions. The dibenzo[a,j]dithieno‐[d,m]coronene 21 exhibits a unique negative curvature (U conformation) with two enantiomers in the solid state. The UV/Vis absorption, fluorescence emission spectra and the DFT‐calculated levels of FMOs of these coronenes mainly depend on the fused aromatic units at the [d,m] edges of the coronene central core; the substituents at the [a,j] positions have less influence. The large variety of (different) fused rings in the coronene core allows the photophysical properties to be fine‐tuned and thus the coronenes′ possible use in organic electronics applications.

Experimental Section

Full details of synthetic procedures and characterization data, NMR spectra, mass spectra, FT‐IR spectra, variable temperature ¹H NMR spectra of compound 21, absorption and emission spectra, cyclovoltammograms, X‐ray crystallographic data as well as the DFT computational details can be found in the Supporting Information.

Deposition Numbers 2088768 (for 23), 2088769 (for 13), 2088770 (for 21), 2088771 (for 14) contain the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service.

Conflict of interest

The authors declare no conflict of interest.

Supporting information

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Supporting Information

X. Yang, F. Rominger, M. Mastalerz, Chem. Eur. J. 2021, 27, 14345.