Sterically induced polymorphism: ON–OFF control of excited-state intramolecular proton transfer (ESIPT) luminescence of 1-methyl-2-(2′-hydroxyphenyl)benzimidazole

Abstract

By introduction of ‘appropriate’ steric hindrance into 2-(2′-hydroxyphenyl)benzimidazole, the obtained compound forms polymorphic crystals based on either intramolecular or intermolecular hydrogen bonding, which respectively show strong ESIPT luminescence (ON state; Φ = 0.74) and practically no luminescence (OFF state; Φ = 0.007). Further, the luminescence can be switched off and on by heating and grinding.