One-Pot Synthesis of Dihydrothiazole-Hydrazone Hybrids and Evaluation of Their Absorption and Emission Properties.

Abstract

A simple, one-pot method for the synthesis of seven novel dihydrothiazole-hydrazone compounds is presented, employing a condensation-cyclization protocol, with the products characterized by FTIR, 1H NMR, 13C NMR, and ESI-MS. Thiazoles and hydrazones are distinguished by versatile chelating properties and fluorescent conjugated scaffolds, and their combination can be considered a promising route to obtaining tunable fluorophores. According to the UV-Vis absorption and fluorescence data, all seven compounds demonstrated absorption maxima at 412-420 nm and emitted a yellow-green light at 554-575 nm. The substituent present at the C-4 position of the dihydrothiazole ring governed the emission wavelength and intensity. Electron-donating groups increased emission intensity and shifted the emission to longer wavelengths, whereas electron-withdrawing groups quenched fluorescence, likely via a photoinduced electron transfer (PET) deactivation mechanism. The Stokes shifts (142-155 nm) also followed the same substituent-dependent pattern. Moderate fluorescence quantum yields (1.64-5.54%) were observed for the thiazoles, indicating that the presence of different functional groups influenced the efficiency of excited-state relaxation. The way substitution influences absorption and emission behavior establishes the dihydrothiazole-hydrazone core as a versatile unit that can be tuned to serve as a fluorophore for sensing, biological, and optoelectronic applications.