Two different mechanisms of stabilization of regular pi-stacks of radicals in switchable dithiazolyl-based materials

Materials based on regular pi-stacks of planar organic radicals are intensively pursued by virtue of their technologically relevant properties. Yet, these pi-stacks are commonly unstable against pi-dimerization. In this computational study, we reveal that regular pi-stacks of planar dithiazolyl radicals can be rendered stable, in some range of temperatures,viatwo different mechanisms. When the radicals of a pi-stack are both longitudinally and latitudinally slipped with respect to each other, the corresponding regular pi-stacked configuration is associated with a locally stable minimum in the potential energy surface of the system. Conversely, those regular pi-stacks in which radicals are latitudinally slipped with respect to each other are stable as a result of a dynamic interconversion between two degenerate dimerized configurations. The existence of two stabilization mechanisms, which can be traced back to the bonding properties of isolated pi-dimers, translates into two different ways of exploiting spin-Peierls-like transitions in switchable dithiazolyl-based materials.