Lanthanide ions as sensitive probes. Part III. Triplet-energy transfer from 2-acetonaphthone and 2-acetylfluorene to europic ions in frozen solution

Transfer of triplet energy from 2-acetonaphthone and 2-acetylfluorene to tervalent europium ions was investigated in rigid glass by measuring the quantum yields of donor phosphorescence and acceptor fluorescence and the decay of donor emission under selective excitation of the ketone at different Eu³⁺ concentrations. It is suggested that transfer originates in the n,π* triplet, which is only slightly above the lowest π,π* triplet of the sensitizer. A suggested photokinetic scheme, consistent with the presumed exchange mechanism, explains the observed behaviour and yields transfer rate constants of 2·3 and 10 | mol^–1 s^–1 for the two sensitizers. Spectroscopic observables predicted by statistical treatments were in very good agreement with experiment and were consistent with the assumed exchange mechanism. Alterations in the predicted time-dependence of phosphorescence intensity by donor self-quenching and by changes in the microscopic decay probability expression are considered.