Spontaneous and photomechanical twisting of a cyanostilbene-based molecular crystal

Abstract

Developing organic molecular crystals with twisted morphology either through spontaneous formation or in response to external stimuli is compelling yet challenging. In this work, we present a cyanostilbene-based molecular crystal, CS–H, which can spontaneously form a twisted morphology through accelerated growth methods or undergo twisting motion from plates to helicoids under UV irradiation. Structural analysis reveals that weak interlayer interactions are critical for the twisting of CS–H crystals. During the fast crystal growth, weak interlayer interactions endow CS–H crystals with the ability to deform adaptively to the defect-induced surface stress and spontaneously form twisted crystals. Upon exposure to UV irradiation, the closely-packed π–π dimers of CS–H molecules in the crystals undergo [2+2] cycloaddition photoreactions, which induce the lattice change and provide the driving forces for crystal twisting. Such crystalline materials with twisted morphology and photomechanical twisting motion hold great potential as actuators in photoresponsive applications.