Synthesis of New Efficient Fluorophores of Thieno[2,3-b]pyridine Series

The reaction of 4-amino-6-aryl-2-halopyridine-3,5-dicarbonitriles with thioglycolic acid ethyl ester was used to synthesize a series of new efficient fluorophores of thieno[2,3-b]pyridine series. The long-wavelength absorption bands of DMSO solutions of the prepared compounds are at the boundary of the UV and visible regions of the spectrum (λabs 375–388 nm) and show an ambiguous influence of the substituent electronic effect, that was explained by quantum chemical calculations. The emission maxima are in the yellow-green region (λem 490– 510 nm) and they are blue-shifted in the presence of electron donor groups with slightly increasing intensity (Φem 37.8–60.6%). It was found that the nitro group presence causes a complete photoluminescence quenching both in solution and in the solid state. In addition, the position of the emission maximum (λem 473–505 nm) and its intensity (Φem 3.6–72.7%) strongly depend on the polarity and the basic properties of the medium, that was established using the Catalan empirical model.