Singlet-triplet transitions system

A direct proof of the reversibility of singlet-triplet transition has been deduced from time-resolved studies of the fluorescence observed under a selective excitation of a and X rovibronic states resulting from the perturbation between (u = 0) and (0= 1) vibronic states in CO. In the former case, the fluorescence shows a biexponential decay, while in the latter one it exhibits an initial induction followed by the decay (Fig. 4 see also Fig. 3 bottom). The ratio of rate constants for the s- l and l- s processes (determined by a simple kinetic treatment) is in a good agreement with the expected thermal distribution after a complete equilibration of the ( + / ) system. ... 

An increase in the ion annihilation exergonicity AG to values comparable to the excited triplet-state energies (AG I LT < 0) opens an additional electron transfer channel (T-route). In the simplest case, only one excited triplet 3 A or 3 D becomes accessible. Triplet emission can be directly observed from the ECL systems involving rare earth and transition metal complexes with allowed (due to extensive spin-orbit coupling) triplet-singlet electronic transition. 

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