Crystal-Structure Control of Molecular Semiconductors by Methylthiolation: Toward Ultrahigh Mobility

Abstract

Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: The crystal structure of organic semiconductors has been regarded as one of the crucial factors for realizing highperformance electronic devices, such as organic field-effect transistors. However, although the control of crystal structures of organic semiconductors has been examined in the last two decades of intensive efforts of the development of organic semiconductors, active measures to control crystal structures enabling high carrier mobility are still limited. In 2016, our research group noticed that regioselective methylthiolation could provide a selective crystal structure change from an ordinary herringbone structure to a pitched π-stacking structure, similar to the crystal structure of rubrene, in the benzo[1,2-b:4,5-b′]dithiophene (BDT) system. Following this serendipitous finding, our group systematically investigated the relationship between the molecular and crystal structures of a range of methylthiolated aromatic and heteroaromatic compounds. This Account provides a comprehensive overview of our research efforts and advancements in the development of methylthiolated small-molecule-based organic semiconductors (molecular semiconductors). We first describe the outline of the past development of molecular semiconductors, focusing on the types of crystal structures of high-performance molecular semiconductors. Then, we describe our findings on the drastic crystal structure change in the BDT system upon methylthiolation, detailing the causes of the change in terms of the intermolecular contacts and intermolecular interaction energies. This is followed by the confirmation of the generality of the crystal-structure change by methylthiolation of a series of acene and heteroacenes, where the herringbone structure in the parent system is unexceptionally transformed into the pitched π-stacking structure, a promising crystal structure for highmobility molecular semiconductors well exemplified by the prototypical molecular semiconductor, rubrene. In fact, the methylthiolated anthradithiophene afforded comparable high mobility to rubrene in single-crystal field-effect transistors. Then, we demonstrate that the sandwich herringbone structures of peri-condensed polycyclic aromatic hydrocarbons, including pyrene, perylene, and peropyrene, change into brickwork crystal structures upon methylthiolation and that, among these compounds, very promising molecular semiconductors, methylthiolated pyrene and peropyrene, showing ultrahigh mobility of 30 cm 2 V s −1 , are realized.Through the studies, by gaining insights into the underlying mechanisms driving the crystal structure changes, we lay a strong foundation for tackling challenges related to controlling the crystal structures and developing high-performance molecular semiconductors. This will be a distinct approach from the past activities in the development of molecular semiconductors that mainly focused on molecules themselves, including their synthesis, properties, and characterization....

MT-pyrene-Based Conductive Radical Cation Salts: Crystal and Electronic Structure and Transport Properties

“…However, the crystal structures of these conducting salts were not fully elucidated, and thus, their electronic structures have been unknown in the last three decades. During the course of our investigation on methylthiolated molecular semiconductors, we have shed light on this “old” but attracting molecule and elucidated that neutral MT-pyrene crystallized into a brickwork structure and showed ultrahigh mobility of greater than 30 cm 2 V –1 s –1 with a band-like transport . The origin of such superior transport property of MT-pyrene was boiled down to the 2D nature of the solid-state electronic structure, which originated in the characteristic brickwork crystal structure (Figure b); the tight-binding band calculations by assuming the quarter-filled state showed the Fermi surface with an anisotropic closed cylinder .…”