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

Theherringbone crystal structures of anthracene and tetraceneare effectively altered into & pi;-stacking-based crystal structures,such as pitched & pi;-stacking, brickwork, and sandwich pitched & pi;-stacking crystal structures, by methylthiolation at the peri-positions. The cause of the structural change was examinedthrough theoretical computations and the analysis of the correspondingchlorinated acenes. The carrier transport properties of the methylthiolatedanthracene and tetracene derivatives are also evaluated by the single-crystalfield-effect transistors. The rational design and control of crystal structuresof organicsemiconductors remain critical challenges in the development of superiororganic semiconductors, yet few studies have focused on these topics.In the present work, we demonstrate that the methylthiolation of acenesat the peri-positions of the terminal benzene rings is a rationaland possibly general approach to realize the rubrene-like pitched & pi;-stacking structure. Among the newly synthesized anthraceneand 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 & pi;-stacking crystal structures.Hirshfeld surface analysis of these crystal structures, in comparisonwith the parent anthracene and tetracene crystal structures, revealedthat the methylthiolation effectively disrupts the CH-& pi;interactions in the parent system and induces the & pi;-stacking.The analysis of the crystal structures of the corresponding chlorinatedanthracenes and tetracenes revealed that, although the chlorinationof acenes similarly disrupts the CH-& pi; interactions andinduces & pi;-stacking, the resulting crystal structures significantlydiffer from those of 1-4. The resultsof natural bond orbital analysis highlight the active role of themethylthio groups of 1-4 in inducingthe pitched & pi;-stacking structures via attractive intermolecularinteractions through S-H intermolecular interactions. The observedeffects of the methylthio groups, which were regioselectively introducedto acenes, will help guide the design of organic semiconductors withcontrolled crystal structures.