Tunable solid-state photoluminescence based on proton-triggered structural transformation of 4,4′-bipyridinium derivative

An organic molecular system with proton-tunable photoluminescence properties based on a mono-substituted bipyridinium derivative 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride, which possesses both pyridine and carboxylic acid groups as proton-responsive units, has been developed. Through controlling the pH value of the self-assembled systems, three compounds with different degrees of protonation have been obtained. These compounds display distinctly different luminescence behaviors and undergo solid-state structural conversion in response to changes in pH values. In particular, luminescence switching triggered by acid–base vapor can be realized.