Semi-empirical study of a set of 2-(2′-hydroxyphenyl)benzazoles using the polarizable continuum model

A set of molecules (2-(2′-hydroxyphenyl)benzoxazol (HBO), 2-(2′-hydroxyphenyl benzothiazole (HBT) and 2-(2′-hydroxyphenyl)benzimidazole (HBI)) exhibiting excited-state intramolecular proton transfer was studied using the polarizable continuum model in low-polar, non-protic solvents (chloroform and carbon tetrachloride), combined with the AM1 semi-empirical molecular orbital method in both gaseous and condensed phase. The heats of formations (ΔHf) are lowered by the solvent effect, especially in chloroform. The increase in the solvent polarity causes an enlargement of the Stokes shift between absorption and emission.