Theoretical investigations on forward-backward ESIPT processes of three fluorophores deriving from 2-(2'-hydroxyphenyl)thiazole

摘要

The photophysical properties and excited-state intramolecular proton transfer (ESIPT) processes for 2-(2'-hydroxyphenyl)- 4-chloromethylthiazole (1), 2-(2'-hydroxyphenyl)-4-phenylthiazole (2), 2-(2'-hydroxyphenyl)-4-hydroxymethyl-thiazole (3) were studied at the TD-B3PW91/6-31 + G(d, p)/IEFPCM level. The structures of 1-3 were fully optimized and the corre- sponding structural parameters, infrared spectra and electron densities in the ground (S0 ) and the first excited (S1 ) states were analyzed. The calculated absorption and fluorescence wavelengths of 1-3 reproduced the experimental data. The potential energy curves of the S0 and S1 states were built and the ESIPT processes were clarified. Our results showed that the intra- molecular H-bonds of 3 and 2 in the S1 state were the strongest and the weakest, respectively, and then the ESIPT potential barriers of 3 and 2 were the lowest and highest, respectively. Among the three phenol-thiazole type probes, the compound 2 with phenyl ring group at the 4 position of the thiazole ring had the larger π-conjugation, and had the higher ESIPT poten- tial barrier at the same time. The corresponding compound 1 and 3 with CH2Cl and CH2OH had the lower ESIPT barrier.