The phosphorescence decay kinetics in the presence of a statistical distribution of molecules over the rates of radiative and non-radiative deactivation of triplet excitations

Approximate formulas of phosphorescence decay kinetics under the conditions of the statistical scatter of molecules over rate constants of radiative or non-radiative deactivation of triplet excitation have been obtained. It is shown that the phosphorescence decay function has different form for these two cases. The obtained difference in kinetics was used to establish the reason for the deviation from the exponential law and faster decay of the sensitized phosphorescence of naphthalene and diphenyl in n-paraffin matrices ( T = 77 K) in the presence of heavy atoms in the donor.

Peculiarities of the Energy Transfer of Electronic Excitation in Carbazolyle-Containing Polymers

Luminescence spectra of poly-N-vinylcarbazole (PVK), poly-N-epoxypropylcarbazole (PEPK), poly-N-vinyl-3-chlorocarbazole (Cl-PVK), and polystyrene (PS) films doped with bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate) iridium [Btp2Ir(acac)] have been studied. The indicated carbazole-containing polymers are promising for the application in electroluminescence devices. The quantum yield of sensitized phosphorescence by Btp2Ir(acac) molecules in carbazole-containing polymer matrices is found to be lower than at their direct excitation in the PS matrix. The additional doping of the PVK-based composite with benzophenone, which transforms some of singlet excitons into triplet ones, diminishes the intensity of the sensitized phosphorescence of Btp2Ir(acac) molecules, which testifies that the efficiency of energy transfer via singlet excitons is higher than via triplet ones. The results obtained can be explained by a competition between the process of energy transfer onto the acceptor site, on the one hand, and the processes of exciton localization at the tail energy states and the trapping of triplet excitons by the products of polymer oxidation, on the other hand. The quantum yield of sensitized phosphorescence by Btp2Ir(acac) molecules in the PVK matrix is found to be almost 1.5 times lower than in the PEPK one. A conclusion is drawn that, in the PVKmatrix, the process of singlet exciton autolocalization at excimer-forming centers followed by the creation of sandwich-like excimers competes with the process of excitation energy transfer onto the acceptor.

Reversible redox modulation of a lanthanide emissive molecular film

Reactive nitrene insertion is utilized in the surface construction of ferrocene-incorporating europium d–f dyads exhibiting a reversible redox switched sensitized phosphorescence.