SPECTRAL AND LUMINESCENT STUDY OF NONRADIATIVE PROCESSES ACCOMPANYINGTHE PHOTOPROTOLYTIC DISSOCIATION OF AMMONIUM FORMS OF COMPLEX ORGANIC-COMPOUNDS

Spectral and luminescent methods (measurements of absorption, excitati on, and fluorescence spectra at 293 K and measurements of spectra, deg rees of polarization, and quantum yields of fluorescence and phosphore scence at 77 K) were used to study specific features of the nonradiati ve deactivation processes accompanying the photoprotolytic dissociatio n of the ammonium forms of aminoderivatives of coumarin, benzanthrone, and polycyclic aromatic hydrocarbons in acidified ethanol solutions. The comparison of absorption and excitation spectra showed that Q, the ratio of the photodissociation rate to the sum of rates of deactivati on processes for the electron-excited S-1 state of an ammonium ion, wh ich compete with photodissociation, decreased in the aromatic amines-3 -aminobenzanthrone-7-aminocoumarins series by at least two orders of m agnitude. The low-temperature measurements were used to estimate the r ate constants of singlet-triplet conversion k(ST) and determine the po sition and the orbital nature of the fluorescent and phosphorescent le vels of the ammonium ions under consideration. The series of compounds under study was found to have a correlation between a decrease of the ratio Q and an increase of k(ST) which gives evidence of a rather str ong competition between the singlet-triplet conversion of ammonium for ms and their photodissociation. It is likely that a sharp increase of k(ST) characterizing a change from 3-ammonium benzanthrone to ammonium forms of coumarin is caused by the inversion of pi pi type S1 level and the n pi type T-2 level.