Multi‐Color Photoluminescence Based on Mechanically and Thermally Induced Liquid‐Crystalline Phase Transitions of a Hydrogen‐Bonded Benzodithiophene Derivative

Controlling assembled structures of pi-conjugated liquid-crystalline molecules is of great interest in the development of stimuli-responsive luminescent materials due to their molecular motility in the ordered states. Herein, we describe a mechanoresponsive hydrogen-bonded benzodithiophene liquid-crystalline molecule that exhibits a tricolor photoluminescence switching at ambient temperature. The compound shows a shear-induced phase transition from a rectangular columnar to a metastable optically anisotropic mesophase, which is accompanied by the luminescent color change from yellow to sky-blue. The metastable mesophase exhibits a time-responsive transformation to another metastable mesophase showing a blue-green emission through isothermal aging at room temperature. The luminescent color of aged sample reverts back to the initial yellow color by thermal annealing at 150 degrees C. These dynamic structural changes accompanied by the emission color changes are governed by distinct pi-stacking modes and hydrogen-bonded patterns. The shear-induced luminescent color change from yellow to blue is found to occur above the shear strain of 390 % at which the shear stress is 2.4x10(5) Pa as determined from dynamic viscoelastic measurements.