Optimizing the white light emission in the solid state isatin and thiazole based molecular hybrids by introduction of variety of substituents on isatin and thiazole ring systems

An efficient and practical 3-component reaction strategy has been developed for the synthesis of a series of multi-colour emissive isatin-thiazole based fluorophores, thiazolylhydrazonoindolin-2-ones (4) from readily available isatins (1), thiosemicarbazide (2) and α-bromoketones (3) in the presence of biodegradable citric acid (0.1 N) in ethanol at reflux temperature for 40-60 min. The reaction proceeds <i>via</i> condensation (C[double bond, length as m-dash]N) and subsequent heterocyclization (C-S & C-N) in one-pot. Nature-friendly reaction profile, easy to perform, wide substrate scope, use of non-hazardous solvents/catalysts, good functional group tolerance, excellent yields (91-98%) in short reaction times, scalability and products do not require column chromatography purification are the attractive features of the present MCR strategy. The photophysical properties of the titled compounds (4) in both solid and solution states have been evaluated. The study reveals that the prepared isatin-thiazole based molecular hybrids exhibited tunable photophysical properties by varying the substituents on both isatin and thiazole motifs. To our delight, the titled compounds, 4k, 4l, 4m, 4u and 4y displayed white light emission with mega Stokes shifts in the solid state.