A theoretical study of the emission spectra of indole and its analogs: indene, benzimidazole, and 7-azaindole

The complete active space (CAS) SCF method and multiconfigurational second- order perturbation theory (CASPT2) have been used to study the electronic s pectra of indole, indene, benzimidazole, and 7-azaindole. The paper is focu sed on the study of the low-lying valence triplet and singlet electronic st ates at the optimized geometries of the excited states. The geometries have been optimized by using analytic CASSCF derivatives. CASPT2 point calculat ions have been performed in order to obtain band origins and relaxed emissi on energies. The results are analyzed in the context of the complex emissio n processes, both fluorescence and phosphorescence, displayed by the title compounds, which can be used as biochemical probes in the characterization of protein properties and activity. (C) 2000 Elsevier Science B.V. All righ ts reserved.