Substituent-directed ESIPT-coupled Aggregation-induced Emission in Near-infrared-emitting Quinazoline Derivatives.

A series of ESIPT (excited state intramolecular proton transfer) active systems (HQz1-HQz6) derived from quinazoline have been reported. The ESIPT emission for these derivatives gets completely quenched in solvents with diverse polarities which have been restored via aggregation-induced emission (AIE) with large Stokes shift (up to 314 nm). It varied from 450 to 701 nm just by altering substituents at the para position of hydroxy group in the central phenyl ring. As well, HQz1-HQz6 displayed solid state emission [∼455 (blue) to ∼704 nm (red)]. The formyl group on the central hydroxy-phenyl ring of these derivatives induces ESIPT by increasing acidity of the hydroxy proton which has been followed by 1 H NMR studies. Further, it has been clearly shown that emission colour and aggregate morphology can be fine tuned by incorporating apt substituents. The present study offers a simple route to obtain colour tunable ESIPT emission via AIE which is very important for biological imaging and fabrication of optoelectronic devices.