Unsymmetrically Extended Polyfused Aromatics Embedding

Letter pubs.acs.org/OrgLett

Unsymmetrically Extended Polyfused Aromatics Embedding Coronene and Perylene Frameworks: Syntheses and Properties Sushil Kumar,† Man-Tzu Ho,‡ and Yu-Tai Tao*,† †

Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan Department of Chemistry, National Central University, Chung-Li 32054, Taiwan

‡

S Supporting Information *

ABSTRACT: A series of polyfused aromatics containing coronene and perylene in their frameworks was successfully constructed by a modified Ramirez−Corey− Fuchs reaction as the key reaction. Typical six-membered annulation and atypical five-membered annulation through controlled reaction conditions led to a range of extensively conjugate aromatics as possible candidates for organic semiconductors. A significant p-type field-effect mobility of 0.42−0.64 cm2/V·s was obtained from one of the derivatives, dibenzo[a,d]coronene.

T

transistor devices were also fabricated for selected samples to demonstrate their potential as charge conducting materials. The major synthetic approaches are displayed in Schemes 1 and 3. In both schemes, similar central key starting polyaryl

he organic skeletons with multiple benzene rings fused together in linear or nonlinear ways have always been a subject of intensive investigations due to their rich electronic properties and potential in diverse applications like nonlinear optics, light-emitting diodes, field-effect transistors, and solar cells.1 The efficiency of charge conduction, photoluminescence, and related material features count on the size, shape, and functional groups decorated around the aromatic core, among others. The packing of these polyaromatics, as determined by the electrostatic, steric, and π−π interactions between neighboring molecules, greatly influence those bulk properties to be used in the organic electronics.2 Thus, the ability to design and synthesize new frameworks of polyfused aromatics is essential to fully explore the potential of these systems. A plethora of synthetic approaches have been developed for highly symmetric polyfused aromatics like linear acenes, perylenes and coronene and their derivatives by Scholl, Clar, Müllen, and others.3 The discovery of a parent coronene framework by Scholl and Meyer in 1932 created a new class of semiconductor materials with the extension of conjugation from the central coronene core.4 For example, the symmetrically extended tetrabenzocoronene, hexa-cata-benzocoronene, hexa-peri-benzocoronene, and/or their ring-substituted derivatives have been reported to give decent field-effect mobility in thin film or single crystal state.5 Extended polyaromatics with perylene as the central core have also been explored in various applications.6 The unsymmetrically extended derivatives remain less explored,7 presumably due to a lack of generalized synthetic strategies toward these compounds. In this work, we report the synthesis and spectroscopic characterization of a number of extended polyaromatics embedding perylene and coronene frameworks using common and uncommon pathways of Scholl reactions on the arylated olefinic derivatives. Field-effect © XXXX American Chemical Society

Scheme 1. Synthesis of Coronene- and Perylene-Embedded Derivatives

olefin derivatives are used (Scheme 2). These olefinic derivatives have been the primary building block in the structural design of many polyaromatic hydrocarbons and also an ideal candidate to study the Scholl reactions due to good solubility and low oxidation potential.8 Many research plans Received: November 15, 2015

A

DOI: 10.1021/acs.orglett.5b03291 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters have been used to prepare these derivatives, featuring their applicability in the oxidative coupling and related reactions. Two powerful tools for the construction of these derivatives are Ramirez−Corey−Fuchs9 and Suzuki coupling or the Barton− Kellogg reaction10−reaction between azomethine and thioketone, followed by dethionation reaction. However, these were either low or even nonyielding for the ketones desired in our design (Scheme 2). For example, when

oxidizing reagents.11 Due to failure of the first two reagents in our case, the derivatives 5−9, 14−18, and 29−31 were subjected to iodine-mediated oxidative coupling under UV irradiation. This nevertheless could not result in complete fusion, even in the presence of higher equivalency of iodine (2.5−5.0). In the case of 5−9 and 14−18, the mixtures could not be purified, while the partially fused derivatives 32 and 33 were isolated in a pure state (Scheme 3).

Scheme 2. Synthesis of Polyaryl Olefins

Scheme 3. Synthesis of Perylene-Embedded Derivatives

thioketone 35 reacted with azomethine 36, the yield of thioepoxide 37 was rather low, at 27%. Additionally, the general Corey−Fuchs reaction on the ketones 2, 11, and 20−22 did not yield the desired dibromo olefin derivatives 3, 12, and 23− 25 by employing triphenylphosphine or the more reactive trialkoxyphosphines. Thus, a synthetic protocol for dibenzocorones and benzonapthoperylenes similar to that for tetrabenzocoronene and hexabenzocoronene cannot be used. Instead, a modified process with carbon tetrachloride and triphenylphosphine as the reagent (1/3/6, mole ratio with respect to the ketone reactant) was found to give the desired dichloro olefin derivatives. In addition, the scope of the reaction was expanded by enforcing a similar strategy on five ketones (2, 11, and 20− 22) to obtain the dichloro olefin derivatives (4, 13, and 26−28) in excellent yields of 78−85% (Scheme 2). The reason for discriminative reactivity of aromatic ketones toward the reagents like carbon tetrabromide and carbon tetrachloride was considered on the basis of low flexibility of the aromatic core in the chosen ketones in accommodating the two bromo atoms on the other side of the double bond. The smaller chlorine atom allows the reaction to proceed smoothly. To prepare the polyarylolefins (5−9, 14−18, and 29−31), the dichloromethylene derivatives were treated with aryl boronic acid employing the palladium-catalyzed Suzuki coupling in the presence of phase-transfer catalyst. The use of phase-transfer catalyst not only reduced the reaction time but also led to purer products. To obtain completely fused derivatives, derivatives 5−9, 14− 18, and 29−31 were subjected to a two-step oxidative coupling strategy using iodine and iron chloride as the catalyst. A variety of reagents is available to carry out oxidative coupling (or cyclodehydrogenation) on these derivatives, like DDQ, iron chloride, or iodine (UV-mediated coupling). The rate of oxidative coupling depends on the oxidation potential of polyaryl olefins, functional groups, and the strength of the

Complete fusion of aryl groups to the desired aromatic nucleus was achieved using iron chloride in nitromethane. Although the coupling reaction carried out by use of Lewis acids are not free from side products from chlorination, polymerization, aryl transfer, or even rearrangement of the desired products,12 higher yields of fully fused products in 71− 85% can be achieved by controlling the reaction time and mole ratio of iron chloride used. The product skeletons were unraveled on the basis of NMR, MALDI-TOF mass, and also crystal XRD analyses for selected ones (Figure S87, SI). The product structures were constructed predominantly through six-membered ring oxidative coupling modes, although as will be elaborated later, abnormal five-membered ring coupling was also observed. The rate of coupling reaction for the polyaryl olefin derivatives was affected by their functional groups, which modulate the oxidation potential. Electron-donating substituents such as methoxy groups on the phenyl rings not only lowered the reaction time but also increased the yields of reactions (Table 1, entries 2, 7, 12, 13), whereas fluoro groups on the phenyls slightly deactivated the aromatic skeleton for the desired coupling reactions. For 3-thienylated derivative 9, an inseparable mixture of annulated and polymerized products was obtained. Additionally, the derivative 18 substituted with a 1naphthyl moiety gave a mixture of annulated products that could not be isolated in pure state. (Table 1, entry 10). The Scholl reaction of derivatives 8 and 17 led to the formation of the DNC and NPP by a regiospecific cyclodehydrogenation reaction. The possible formation of the other analogous hydrocarbons such as DNC1 or DNC2 was ruled out on the basis of the NMR and single-crystal XRD data. When the Scholl reaction was applied on tetraphenyl-olefin 32, a rare cyclodehydrogenation reaction with five-membered ring coupling gave indenoperylene derivative Ph-BINP in an excellent yield of 80%. One phenyl group remained unfused in B

DOI: 10.1021/acs.orglett.5b03291 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters

depend on the concentration and the nature of the solvent.16 This phenomenon was also observed for perylene derivative Met-BFP, when concentration-dependent NMR spectra were taken in solvents like DMSO-d6 (Figure S89a, SI). Significant shifting and merging of NMR signals were observed upon increasing the derivative concentration in solution. The aggregation in this derivative can be explained based on the increased dipole moment and planarization of the molecule after fusion from the precursors A and B (Figure S89b, SI). The DBC and BNP derivatives displayed light-yellow to yellow color, while indeno- and fluorenthrenoperylene derivatives gave orange color in their solid states. Absorption spectra of the derivatives as recorded in dilute dichloromethane solutions are illustrated in Figure 1a and S90−91, while related

Table 1. Conversion of Aryl Olefins to Fused Derivatives through Oxidative Coupling Reactions entry

reactant

product

yieldc (%)

timed (h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

5 6 7 8 9 14 15 16 17 18 32 33 33 34

DBC Met-DBC Flu-DBC DNC mixturea BNP Met-BNP Flu-BNP NPP mixtureb Ph-BINP Met-PhBNP Met-BFP Met-BBFNP

76 81 65 77

24 6 20 12 12 24 6 24 12 24 36 4 12 24

70 85 69 71 80 81 82

a

Compound DTC could not be isolated pure. bIn this case, mixtures of derivatives were obtained. c,dYields and time are given for iron chloride-mediated oxidative coupling reactions.

this derivative even with excessive iron chloride, which also led to polymerization. Indeed, very few reports on this unexpected five-membered oxidative coupling are known. One precedent was described by Mü llen et al. in their synthesis of benzoindenoperylene from structurally common naphthalene derivatives using Lewis acids like FeCl3 and AlCl3 at room and elevated temperatures, respectively.13 The derivative 33 carrying methoxy groups produced fluorenthrenoperylene derivative Met-BFP via successive six-, five-, and six-membered cyclodehydrogenation reactions (Table 1, entry 12). Additionally, we were able to isolate pure Met-PhBNP with only 1-fold oxidative coupling reaction on 33 with a shorter reaction time of 4 h. In order to rationalize the formation of Ph-BINP and DNC, two plausible mechanisms are suggested (Schemes S4 and S5, SI). The loss of one electron from the partially fused derivative 29 can result in a cation radical that allows the six- or fivemembered ring fusion reactions. The existence of cation− radical intermediates in the oxidative coupling reactions is already well-acknowledged.14 In the 3,9-substituted polyaryl olefins 31−33, the five-membered ring closure occurred possibly due to difference in electron-richness7,12b on the benzoanthracene unit. The formation of the DNC was attributed to the higher reactivity of 1-position as compared to the 3-position of naphthyl unit, resulting from the resonance stabilization of cation-radicals. The chemical transformation of polyaryl olefins into their ring-fused analogous was confirmed for DNC and PhBINP derivatives based on their single-crystal XRD analyses (Figure S88, SI). Indenoperylene derivative PhBINP was found to be slightly twisted due to steric hindrance at the bridging positions. An efficient π−π overlap (overlap distance, 3.378 Å) was observed among polyaromatic segments in the crystal packing. Similarly, the X-ray crystal structure of DNC showed that the molecule was twisted at the naphthyl bridge, while there was efficient cofacial packing among the coronene units, with an interplanar distance of 3.3 Å. Owing to their planar aromatic skeletons and polar functional groups, some perylenes15 and other polyaromatic derivatives exhibit aggregation behavior in their solution states. Different stacking patterns such as J- and H-aggregates form

Figure 1. (a, b) Normalized absorption and emission spectra as recorded in dichloromethane.

data is summarized in Table S1 (SI). Coronene hydrocarbon exhibits four absorption bands in the region of ∼250−350 nm, with the maximum absorption observed at ∼300 nm. The absorption featured were assigned to be attributed due to the π−π* electronic transitions of coronene core. 17 The dibenzocoronene DBC displayed a bathochromic shift in absorption profile, with the structurally analogous absorption pattern centered at 293, 330, 379, and 399 nm. Thus, absorption features of both coronene and DBC are best described by similar electronic states with different energies. Perylene hydrocarbon shows absorption in the range of ∼250− 435 nm,18 whereas benzonaphthoperylene, indenoperylene, and fluorenthrenoperylene derivatives afford structurally similar but shifted absorption maxima toward higher wavelength region presumably due to extension of conjugation. In perylene derivatives, the HOMO is primarily localized in the perylene unit, indicating the electronic transitions could best be attributed by this core (Figure S95, SI). The DBC and BNP derivatives displayed blue to blue-green, Ph-BINP yellow, while Met-BFP orange emissions in their dilute solutions Figure 1b and S92−93, SI). In the derivatives BNP to Met-BFP, the emission color shifts from blue to orange presumably due to increased conjugation. To demonstrate the potential of these polyfused aromatics, single-crystal field-effect transistors (SCFETs) were fabricated with one of the derivatives. Thus, rod-shaped single crystals of the derivative DBC were obtained by the physical vapor transport method at 360 °C using helium as the carrier gas. A top-contact, top-gate SCFET was fabricated by laminating the crystal on a glass substrate with painted colloidal graphite as the source and drain, perylene as the dielectric, and colloidal graphite on its top as the gate electrode. The channel length, width, and perylene thickness were 1.0−0.5 mm, 0.25−0.20 mm, and 1.8−2.5 μm, respectively. An average mobility of 0.42 cm2/V·s and maximum mobility of 0.64 cm2/V·s were obtained for DBC (Figures S96−98 and Table S2, SI). C

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(7) Kelber, J.; Achard, M.-F.; Durola, F.; Bock, H. Angew. Chem., Int. Ed. 2012, 51, 5200−5203. (8) (a) Wu, Y.-T.; Kuo, M.-Y.; Chang, Y.-T.; Shin, C.-C.; Wu, T.-C.; Tai, C.-C.; Cheng, T.-H.; Liu, W.-S. Angew. Chem., Int. Ed. 2008, 47, 9891−9894. (b) Kumar, S.; Tao, Y.-T. J. Org. Chem. 2015, 80, 5066− 5076. (9) (a) Desai, N. B.; McKelvie, N.; Ramirez, F. J. Am. Chem. Soc. 1962, 84, 1745−1747. (b) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 13, 3769−3772. (10) (a) Plunkett, K. N.; Godula, K.; Nuckolls, C.; Tremblay, N.; Whalley, A. C.; Xiao, S. Org. Lett. 2009, 11, 2225−2228. (11) (a) Grzybowski, M.; Skonieczny, K.; Butenschön, H.; Gryko, D. T. Angew. Chem., Int. Ed. 2013, 52, 9900−9930. (b) Zhang, X.; Jiang, X.; Zhang, K.; Mao, L.; Luo, J.; Chi, C.; Chan, H. S. O.; Wu, J. J. Org. Chem. 2010, 75, 8069−8077. (12) Sarhan, A. A. O.; Bolm, C. Chem. Soc. Rev. 2009, 38, 2730− 2744. (b) Rempala, P.; Kroulík, J.; King, B. T. J. Am. Chem. Soc. 2004, 126, 15002−15003. (c) Pradhan, A.; Dechambenoit, P.; Bock, H.; Durola, F. J. Org. Chem. 2013, 78, 2266−2274. (13) Avlasevich, Y.; Kohl, C.; Müllen, K. J. Mater. Chem. 2006, 16, 1053−1057. (14) (a) Rempala, P.; Kroulík, J.; King, B. T. J. Org. Chem. 2006, 71, 5067−5081. (b) Clowes, G. A. J. Chem. Soc. C 1968, 2519−2526. (c) Zhai, L.; Shukla, R.; Wadumethrige, S.; Rathore, R. J. Org. Chem. 2010, 75, 4748−4760. (15) (a) Sugiyasu, K.; Fujita, N.; Shinkai, S. Angew. Chem. 2004, 116, 1249−1249. (b) Shin, W. S.; Jeong, H.-H.; Kim, M.-K.; Jin, S. H.; Kim, M.-R.; Lee, J.-K.; Lee, J. W.; Gal, Y.-S. J. Mater. Chem. 2006, 16, 384− 390. (16) (a) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev. 2011, 40, 5361−5388. (17) Hirayama, S.; Sakai, H.; Araki, Y.; Tanaka, M.; Imakawa, M.; Wada, T.; Takenobu, T.; Hasobe, T. Chem. - Eur. J. 2014, 20, 9081− 9093. (18) McCusker, C. E.; Castellano, F. N. Chem. Commun. 2013, 49, 3537−3539.

In conclusion, we have successfully synthesized new series of polyfused aromatics containing perylene and coronene frameworks through a multistep synthetic approach involving new ways of utilizing Scholl reactions. Newly constructed derivatives are well characterized by spectroscopic techniques such as NMR and MALDI−mass techniques. The chemical structures of DBC, Flu-DBC, DNC, and Ph-BINP were confirmed by single-crystal XRD analysis and were found to have face-to-face packing arrangements. One of the derivatives DBC (dibenzocorone) gave an average p-type field-effect mobility of 0.42 cm2/V·s.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.5b03291. Detailed experimental procedures and complete spectroscopic analysis (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +886-2-27831237. Tel: +886-2-27898580. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Ministry of Science and Technology, Taiwan (Grant No. 103-2120-M-009-003-CC1) is gratefully acknowledged.

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REFERENCES

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DOI: 10.1021/acs.orglett.5b03291 Org. Lett. XXXX, XXX, XXX−XXX