Configuration of 2-(2-thienyl)-5-aryloxazoles in their ground and excited states

The electronic absorption and emission spectra of a series of 2-(2-thienyl)-5-aryloxazoles in solutions, vapors, and matrices (ethanol-ether, 77 K) have been studied, and the fluorescence quantum yields have been determined. The basicity constants in aqueous solutions in the ground state have been measured spectrophotometrically. The set of spectroscopic data indicate that the configuration of the 2-(2-thienyl)-5-aryloxazoles in the ground state is nearly planar and is practically independent of the temperature and the state of aggregation. Conversely, in the excited state the configuration of these molecules is generally nonplanar and depends on external factors.