Crystal structures of dimethoxyanthracens: a clue to a rational design of packing structures of π-conjugated molecules.

We carried out a systematic investigation of packing structures of a series of dimethoxyanthracenes, i.e., 1,4- ( 1 ), 1,8- ( 2 ), 1,5- ( 3 ), 2,6- ( 4 ), and 2,7- derivative ( 5 ). The packing structures of the dimethoxyanthracenes are classified into two types, a rubrene-like pitched π-stack ( 1 - 3 ) and a typical herringbone packing ( 4 and 5 ), which evidently show that the position of methoxy groups is crucial to determine the packing structure of dimethoxyanthracenes. Effects of the substitution position on intermolecular interactions are analyzed by the noncovalent intermolecular interaction (NCI) method, Hirshfeld surface analysis, and symmetry-adapted perturbation theory (SAPT) method, thus clarifying active roles of the mthoxy groups in the formation of rubrene-like pitched π-stack. The present results shed light on a molecular design strategy to realize the rubrene-like pitched π-stack in the solid state, which had been regarded as a packing structure limited for rubrene and its closely related derivatives.