Regularities of the processes of radiationless conversion in polyatomic molecules

The processes of radiationless conversion in aromatic and heteroaromatic molecules are investigated theoretically. The values of constant rates of internal conversion are calculated. The theoretical estimation of constant rates of S–T conversion aromatic hydrocarbon molecules and in their carbonyl-, thiocarbonyl-, and nitroderivatives and in azaheterocyclic molecules are given. The S-T conversion probability between the states of different orbital nature (nπ* and ππ*) is equal to ca. 10¹⁰–10¹¹ sec^?1 that is two to four orders higher than the conversion probability between the states of the same orbital nature. It is shown that the process of T-S conversion may be described in the second and in the highest orders of perturbation theory. The luminescent characteristics of molecules are connected with the relative position of electron states of different orbital nature and multiplicity and conversion characteristics.