Heterocyclic dyes displaying excited-state intramolecular proton-transfer reactions (ESIPT): computational study of the substitution effect on the electronic absorption spectra of 2-(2 '-hydroxyphenyl)-1,3-benzoxazole derivatives

Semi-empirical molecular-orbital methods were used to simulate the electron ic absorption spectra of a series of 2-(2'-hydroxyphenyl)-1,3-benzoxazole d erivatives, namely AMI and MNDO-PM3 for geometry optimization and INDO/S-CI and HAM/3 for spectroscopic features. Wavelengths of maximum absorption th at agree better with experimental data were found when INDO/S-CI was applie d to PM3-generated inputs. Chemical substitution redshifted the absorption spectrum of all the model compounds, a feature discussed based on the calcu lated energy levels of frontier orbitals and charge redistribution upon ele ctronic excitation.