Polymorph-dependent solid-state fluorescence and selective metal-ion-sensor properties of 2-(2-hydroxyphenyl)-4(3H)-quinazolinone.

2-(2-Hydroxy-phenyl)-4(3H)-quinazolinone (HPQ), an organic fluorescent material that exhibits fluorescence by the excited-state intramolecular proton-transfer (ESIPT) mechanism, forms two different polymorphs in tetrahydrofuran. The conformational twist between the phenyl and quinazolinone rings of HPQ leads to different molecular packing in the solid state, giving structures that show solid-state fluorescence at 497 and 511 nm. HPQ also shows intense fluorescence in dimethyl formamide (DMF) solution and selectively detects Zn(2+) and Cd(2+) ions at micromolar concentrations in DMF. Importantly, HPQ not only detects Zn(2+) and Cd(2+) ions selectively, but it also distinguishes between the metal ions with a fluorescence λ(max) that is blue-shifted from 497 to 420 and 426 nm for Zn(2+) and Cd(2+) ions, respectively. Hence, tunable solid-state fluorescence and selective metal-ion-sensor properties were demonstrated in a single organic material.