Indeno[1,2-b]fluorenes (IFs), while containing 4n π-electrons, are best described as two aromatic benzene rings fused to a weakly paratropic s-indacene core. In this study, we find that replacement of the outer benzene rings of an IF with benzothiophenes allows the antiaromaticity of the central s-indacene to strongly reassert itself. Herein we report a combined synthetic, computational, structural, and materials study of anti- and syn-indacenodibenzothiophenes (IDBTs). We have developed an efficient and scalable synthesis for preparation of a series of aryl- and ethynyl-substituted IDBTs. NICS-XY scans and ACID calculations reveal an increasingly antiaromatic core from [1,2-b]IF to anti-IDBT, with syn-IDBT being nearly as antiaromatic as the parent s-indacene. As an initial evaluation, the intermolecular electronic couplings and electronic band structure of a diethynyl anti-IDBT derivative reveal the potential for hole and/or electron transport. OFETs constructed using this molecule show the highest hole mobilities yet achieved for a fully conjugated IF derivative.
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We thank the National Science Foundation (CHE-1301485) for support of the U Oregon research, as well as for support in the form of an instrumentation grant (CHE-1427987). The device studies at WFU were supported by the National Science Foundation under grant ECCS-1254757. C. R. thanks the University of Kentucky Vice President for Research for start-up funds, and Dr Gjergji Sini for fruitful discussions. K. U. was partly supported by the Osaka University Scholarship for Short-term Overseas Research Activities 2013. HRMS were obtained at the Mass Spectrometry Facilities and Services Core of the Environmental Health Sciences Center, Oregon State University, supported by grant #L30-CS00210, National Institute of Environmental Health Sciences, National Institutes of Health.
Electronic supplementary information (ESI) available: Experimental details, spectroscopic data, computational details, device details and copies of 1H and 13C NMR spectra. CCDC 1451107–1451110. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc00950f
Marshall, Jonathan L.; Uchida, Kazuyuki; Frederickson, Conerd K.; Schütt, Christian; Zeidell, Andrew M.; Goetz, Katelyn P.; Finn, Tristan W.; Jarolimek, Karol; Zakharov, Lev N.; Risko, Chad; Herges, Rainer; Jurchescu, Oana D.; and Haley, Michael M., "Indacenodibenzothiophenes: Synthesis, Optoelectronic Properties and Materials Applications of Molecules with Strong Antiaromatic Character" (2016). Chemistry Faculty Publications. 86.