Abstract
A transition-metal catalyzed alkyne benzannulation allowed an unprecedented synthesis of circumpyrene, starting from 3,11-dibromo-6,14-dimesityldibenzo[hi,st]ovalene (DBOV). The circumpyrene was characterized by a combination of NMR, mass spectrometry, and single-crystal X-ray diffraction analysis, revealing its multizigzag-edged structure. Two newly introduced C═C bonds in circumpyrene strongly perturbed the electronic structures of DBOV, as evidenced by increased optical and electrochemical energy gaps. This is in good agreement with an increased number of Clar's sextets as well as a decreased number of π-electrons in the conjugation pathway of circumpyrene, according to anisotropy of the induced current density (ACID) calculations. The present approach opens a new avenue to multizigzag-edged nanographenes and offers insights into their (opto)electronic properties.
Highlights
Two newly introduced C C bonds in circumpyrene strongly perturbed the electronic structures of DBOV, as evidenced by increased optical and electrochemical energy gaps
The smallest circumarenes, namely circumbenzene[30−34] and circumnaphthalene,[35] were synthesized by Scholl and Clar, respectively, and their soluble derivatives were later employed in supramolecular self-assembly andelectronic device studies.[36−38] A larger circumanthracene was first synthesized by Diederich and colleagues,[39] and its tetracyano derivative was more recently reported by Feng
Reactions occurring at bay regions of polycyclic aromatic hydrocarbons (PAHs), such as intramolecular Friedel−Crafts alkylation,[41−43] Diels−Alder cycloaddition,[30,35] and cyclization of preinstalled ethynyl bonds,[36] permit this obstacle to be surmounted and are capable of building extended aromatic cores
Summary
Nanographenes, extended, nanosized, polycyclic aromatic hydrocarbons (PAHs), exhibit unique and structuredependent electronic, optical, and magnetic properties,[1−3] highlighting their potential as next-generation carbon materials for photonics, (opto)electronics, and spintronics.[4−10] Nanographenes having both zigzag edges (L-regions) and armchair edges (with bay-regions), e.g. periacenes, anthenes, and zethrenes, have attracted particular attention because of their low energy gaps and/or open-shell characters.[11−18] On the other hand, multizigzag-edged nanographenes, consisting only of zigzag edges and K-regions, without bay regions, have been frequent targets of theoretical studies.[19−28] there are still a limited number of synthesized examples, precluding detailed experimental investigations.[29]. This is in good agreement with an increased number of Clar’s sextets as well as a decreased number of π-electrons in the conjugation pathway of circumpyrene, according to anisotropy of the induced current density (ACID) calculations.
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