ON THE INDIRECT DETERMINATION OF TRIPLET ENERGIES AND LIFETIMES BY THE TRIPLET-QUENCHING METHOD - A REEVALUATION OF LITERATURE DATA ON THE TRIPLET-STATE OF AZULENE

The indirect determination of a triplet energy by the triplet-quenching method is based on reversible triplet energy transfer (TET). In the TET from a donor D to an acceptor A, two kinds of reversibility are to be distinguished: the geminate reversibility in an encounter pair, 3D* ... 1A half arrow right over half arrow left 1D ... 3A*, and the nongeminate reversibility after dissociation of a pair in 1D and 3A*. With azulene as triplet energy acceptor, the nongeminate reversibility of TET must not be neglected; it is essential for obtaining reliable estimates of the triplet energy and of the order of magnitude of the triplet lifetime. With one exception, a reevaluation of literature data gives good agreement of the indirectly determined triplet energy of azulene with the value obtained from the 0,0 transition of the phosphorescence.