Methylthiolation of Acenes: Change of Crystal Structure from Herringbone to Rubrene-like Pitched π-Stacking Structure

The rational design and control of crystal structures of organic semiconductors remain critical challenges in the development of superior organic semiconductors, yet few studies have focused on these topics. In the present work, we demonstrate that the methylthiolation of acenes at the peri-positions of the terminal benzene rings is a rational and possibly general approach to realize the rubrene-like pitched π-stacking structure. Among the newly synthesized anthracene and tetracene derivatives, bis(methylthio)anthracene, bis(methylthio)tetracene, and tetrakis(methylthio)tetracene (1, 3, and 4), but not tetrakis(methylthio)anthracene (2), were found to have pitched π-stacking crystal structures. Hirshfeld surface analysis of these crystal structures, in comparison with the parent anthracene and tetracene crystal structures, revealed that the methylthiolation effectively disrupts the CH−π interactions in the parent system and induces the π-stacking. The analysis of the crystal structures of the corresponding chlorinated anthracenes and tetracenes revealed that, although the chlorination of acenes similarly disrupts the CH−π interactions and induces π-stacking, the resulting crystal structures significantly differ from those of 1–4. The results of natural bond orbital analysis highlight the active role of the methylthio groups of 1–4 in inducing the pitched π-stacking structures via attractive intermolecular interactions through S–H intermolecular interactions. The observed effects of the methylthio groups, which were regioselectively introduced to acenes, will help guide the design of organic semiconductors with controlled crystal structures.