Mechanical-force-induced thermochromic-to-photochromic conversion of a coupled Schiff base hinged via a biphenyl moiety†

A biphenyl-linked dimeric Schiff base (bis-SACz) demonstrated exclusive thermochromism in its crystalline state but transformed to a photochromic amorphous state upon being subjected to grinding. By contrast, the corresponding monomer (SACz) lacked this behavior, highlighting the unique function of the biphenyl group. Quantum chemical calculations suggested enhanced thermochromism due to a significant energy level alignment.