Limits to the applicability of the rule of equality to unity of the sum of quantum yields of fluorescence and transition to the triplet state for complex organic molecules in the condensed phase (A review)

摘要

For different classes of molecules, we have estimated from experimental data the lower limit of the height of S (1) levels for which the rule q (fl) + q (T) = 1 (q (fl) is the fluorescence quantum yield, q (T) is the quantum yield of formation of the triplet state) begins to be violated; i.e., direct nonradiative transition from the S (1)-state to the ground state appears, the quantum yield of which exceeds measurement errors. We have found that, for compounds of different classes, this limit varies from 15000 to 21000 cm(-1). It has been shown that the difference in the limit may be explained in terms of the inductive resonance theory of nonradiative transitions, which takes into account the localization of the electronic transition, its rate constant, and the overlap of the vibronic spectrum of the molecule with the vibrational spectrum of high-frequency vibrations taking into account the variation in the rate constant of the intersystem crossing transition to the triplet state.