Synthesis and Solvatochromism of New Thiazole Derivatives Bearing N,N-Bis(2-methoxyethyl) Benzenesulfonamide Moiety.

New thiazole derivatives containing N, N-bis(2-methoxyethyl)benzenesulfonamide groups at the C(4) atom and amino groups bearing electron-donating and electron-withdrawing substituents at the C(2) atom of the heterocycle were obtained via a three-step synthetic method. The sulfonamide intermediate compounds were synthesized with a disubstituted amine of bis(2-methoxyethyl)amine and dibrominated intermediates were obtained via the reaction of bromine. The final step of the Hantzsch thiazole synthesis via different thiourea derivatives yielded the desired thiazole derivatives. In addition, their absorption, emission and solvatochromic properties were examined in several solvents. All compounds presented large Stokes' shift values within the range of 5020-11,974 cm⁻¹ and excellent photostabilities which are important characteristics of fluorophores. The o-methoxyphenylamino substituted thiazole displayed the largest Stokes' shift value of 11,974 cm⁻¹ in methanol suggesting that the molecule was highly polarized in the excited state. They are dependent on solvent polarity and generally display bathochromic shifts in polar solvents with a linear correlation in the fluorescence wavenumbers and the Stokes' shift values versus the empirical parameter values of solvent polarity and solvent polarity parameter values. Notably, the excited state dipole moment was greater than the dipole moment in the ground state. The Kamlet-Taft analysis revealed that the solvatochromic response of thiazole derivatives were closely related to the solvent polarity, ability of H-bonding, and electron-donating and withdrawing groups on the benzene ring. The Catalán model was employed to investigate solvent effects on structural variations among the studied compounds, revealing that the type and position of substituent affected dipolarity, polarizability, and hydrogen bonding capabilities.