Isoelectronic Substitution of a High‐performance Organic Semiconductor with Selenium Atoms: Synthesis and Characterization of Methylthiolated Dibenzo[cd,gh][2,5]diselenapentalene

Abstract

A selenium variant of one of the best molecular semiconductors, 1,3,6,8‐tetrakis(methylthio)pyrene (MT‐pyrene), namely 1,3,5,7‐tetrakis(methylthio)dibenzo[cd,gh][2,5]diselenapentalene (1), was designed, synthesized, and fully characterized through single‐crystal X‐ray analysis and single‐crystal field‐effect transistors. Although the crystal structure of 1 was a brickwork‐related structure similar to that of MT‐pyrene, the transport properties of 1 were far inferior to that of MT‐pyrene. This is attributed to subtle differences in the crystal structure, where the large displacement along the molecular short‐axis direction diminishes the efficient two‐dimensional overlap of HOMO. Since such displacement can be caused by steric congestion of three chalcogen atoms at both sides of 1, two from the methylthio group and one from the core, we also synthesized 1,5‐bis(methylthio)dibenzo[cd,gh][2,5]diselenapentalene (2). However, 2 gave a less intermolecularly interactive crystal structure or one‐dimensional anisotropic structure, which were also not promising as molecular semiconductors, judging from the calculated electronic structures in the solid state. As the selenium‐containing core, dibenzo[cd,gh][2,5]diselenapentalene, has an isoelectronic molecular structure with pyrene and a smaller reorganization energy than pyrene, it is expected to be a promising π‐conjugated structure as organic semiconductors. However, methylthiolation was concluded not to be a suitable molecular‐design strategy to bring out the potential of the core.