Unraveling two distinct polymorph transition mechanisms in one n-type single crystal for dynamic electronics

Cooperative transitions have acquired much attention for low transition barriers, ultrafast kinetics, and structural reversibility but cooperative transitions are rare in molecular crystals and their origin is poorly understood. Here the authors show that reorientation of the alkyl side chains in a 2-dimensional quinoidal terthiophene triggers cooperative behavior, and establish alkyl chain engineering to control the polymorphic behavior.