Solution-and solid-state emitters with large Stokes shifts combining pyrene and 4-hydroxythiazole fluorophores

•Pyrenyl-substituted “push–pull” 4-RO-thiazoles were synthesized.•They exhibits fluorescence in solution at 598–626 nm with quantum yields 0.19–0.29.•Large Stokes shifts (up to 8500 cm−1) were observed.•Solid-state fluorescence at ∼590–640 nm with quantum yields 0.04–0.15 was observed.•Time-resolved fluorescence, (TD)DFT and X-ray-diffraction studies were performed.

4-Hydroxy-5-nitrophenyl-2-(pyren-1-yl)thiazole and a series of its O-substituted derivatives were synthesised. These compounds are fluorescent in solution, emitting light in the region 598–626 nm with quantum yields 0.19–0.29. Large Stokes shifts, approaching 8500 cm−1, were explained by the intramolecular charge transfer character of the lowest excited state, confirmed by TD DFT calculations. The O-substituted compounds also exhibited fluorescence in the solid state. The lack of solid-state emissive properties of the parent hydroxythiazole and the emission of its O-acetyl derivative are discussed in terms of their crystal packings.

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