Extension of the π-conjugated core of methylchalcogenolated polycyclic aromatic hydrocarbon: synthesis and characterization of 1,4,7,10-tetrakis(methylthio)- and tetramethoxy-coronene

Abstract

Controlling the crystal structures of polycyclic aromatic hydrocarbons (PAHs) by regioselective methyl chalcogenolation is an effective strategy for realizing superior molecular semiconductors showing ultrahigh mobility, as exemplified by methylthiolated pyrene and peropyrene. Following the strategy, we designed and synthesized 1,4,7,10-tetrakis(methylthio)coronene (MT-coronene) and 1,4,7,10-tetramethoxycoronene (MO-coronene) as potential candidates for high-performance molecular semiconductors. Since the coronene core is highly symmetric, the regioselective functionalization at the 1,4,7,10-positions seemed to be challenging, and thus, we tested two strategies for constructing such regio-selectively functionalized coronene derivatives; one was the direct functionalization of parent coronene via the iridium-catalyzed borylation reaction, and the other was the stepwise construction of the coronene core with functionalized naphthalene derivatives. Interestingly, the former was suitable for the synthesis of MT-coronene, whereas the latter was suitable for MO-coronene. The crystal structures of MT- and MO-coronene were significantly different from the γ-structure of their parent and classified into the brickwork and the sandwich herringbone structure, respectively. In accordance with the brickwork crystal structures with isotropic but small intermolecular HOMO overlaps, the MT-coronene-based single-crystal field-effect transistors (SC-FETs) showed decent transistor responses with the carrier mobility of up to 0.5 cm² V^–1s^–1. On the other hand, the SC-FETs of MO-coronene, the solid-state electronic structure of which was zero-dimensional due to the sandwich herringbone structure, were far inferior to those of MT-coronene. Based on the crystal structures and theoretical calculations on MT- and MO-coronene, we analyzed the tendency of the intermolecular interactions and intermolecular HOMO overlaps in the solid state, which explains the performances of the coronene system as molecular semiconductors. Furthermore, we compared the solid-state structures of a series of methylthiolated PAHs, pyrene, perylene, peropyrene, and coronene, to figure out the differences in the performances as molecular semiconductors, which gave us new insights into the relationship between the molecular, packing, and electronic structure in the solid state, showing viewpoints for superior molecular semiconductors.