Crystal structures of molecular semiconductors: control and prediction Kazuo Takimiya Tohoku University and RIKEN CEMS, N.A., Japan The crystal structure critically affects the carrier transport properties of molecular semiconductors. However, it is vertically impossible to predict the crystal structures of molecular semiconductors, which has been one of the obstacles to developing high-performance molecular semiconductors. Thus, it is highly desirable to develop practical methods to accurately predict the crystal structures of given molecular semiconductors before synthesizing molecules, which is the most time-consuming and labor-intensive process. To tackle this, we are approaching the issue both from the experimental and computational points of view. From the experimental viewpoint, we found the effect of regio-selective methylthiolation to "manipulate" crystal structures of molecular semiconductors. The organic semiconductors with the herringbone crystal structure, like acenes and thienoacenes, crystalize into the rubrene-like pitched pi-stacking structure by methylthiolation at the particular position [1] . On the other hand, peri -condensed polycyclic aromatic hydrocarbons (PAHs), such as pyrene and perylene, upon regio-selective methylthiolation, crystalize into the brickwork structures, enabling ultrahigh mobility of 30 cm 2 V –1 s –1 in 1,3,6,8-tetrakis(methylthio)pyrene based field-effect transistors [2] . In our computational approach, on the other hand, we developed a simple and intuitive way to simulate the brickwork crystal structures of methylthiolated peri -condensed PAHs. Using the method, we can simulate the crystal structures of a range of methylthiolated peri -condensed PAHs, leading to a new high-performance molecular semiconductor showing mobility of up to 30 cm 2 V –1 s –1 [3] . With these experimental and computational results, we will discuss the possibility of molecular design by crystal structure simulations. References 1. C. Wang, K. Takimiya et al ., Chem. Sci . 2020 , 11 , 1573; K. Kanazawa, K. Bulgarevich, K. Kawabata, K. Takimiya, Cryst. Growth Des ., in press (DOI: 10.1021/acs.cgd.3c00525). 2. K. Takimiya, K. Bulgarevich, et al ., Adv. Mater . 2021 , 33 , 2102914. 3. K. Bulgarevich, S. Horiuchi, K. Takimiya, Adv. Mater. , in press (DOI: 10.1002/adma.202305548).
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