Photophysics and Mechanisms of Intramolecular Electronic Energy Transfer in Bichromophoric Molecular Systems: Solution and Supersonic Jet Studies.

This paper investigates the direct, incoherent energy transfer due to exchange from an excited donor to randomly distributed acceptors. Making use of a general, exact formula for the time and concentration dependent ensemble averaged decay [Blumen and Manz, J. Chem. Phys. 71,4694(1979) ] simple approximate expressions for the limiting cases, of low and high concentrations and of short and long times, also under the inclusion of the back‐transfer in the pair approximation, are derived; for low acceptor concentrations and long times the results of Inokuti and Hirayama [J. Chem. Phys. 43, 1978 (1965)] generalized to arbitrary dimensions, are retrieved. The limits of validity of the different approximations are determined by a numerical evaluation of the exact formula for particular lattices of interest.

On the direct energy transfer via exchange to randomly distributed acceptors

This paper studies the decay law of the excitation of a donor molecule, due to its microscopic long range interactions with moving acceptor molecules. Particular attention is given to the case of acceptor molecules randomly dispersed in a host liquid. From a general approach we derive an exact ensemble averaged formula for the decay of the donor excitation as a function of the molecular motion. The expression obtained is valid for all types of microscopic molecular interactions and for arbitrary ratios of acceptors to inert molecules; from this formula we determine the energy decay for motions which are slow or rapid relatively to the microscopic energy transfer times. If the motion is frozen, we retrieve the decay law valid for acceptors imbedded randomly in a solid matrix [A. Blumen and J. Manz, J. Chem. Phys. (to be published)]. For slow molecular displacements, which obey the Langevin equations of Brownian motion, the diffusion dependent decay law is presented; in the case of low acceptor concentration and multipolar interactions the expression reduces to the Yokota and Tanimoto result [J. Phys. Soc. Jpn 22, 779 (1967)], generalized to spaces of arbitrary dimensions. In the case of rapid motion, the decay becomes motion independent, and is not diffusion controlled.

On the direct energy transfer to moving acceptors

The dynamics of luminescence decay is analyzed within the general scenario of randomly distributed ions with whatever multipole interaction, taking into account energy transfer and migration processes among them. By applying Pade approximants to the Allinger and Blumen expression for the excited state population, a simple expression has been obtained which can be easily fitted to experimental data. This expression can be considered a generalization of the dipole–dipole Yokota–Tanimoto equation. On the other hand, the decay curves from the 5D3 level of the Tb3+ ions in fluorozincate glasses have been measured for different Tb3+ concentrations. The results are analyzed in the framework of the proposed expression.

Energy transfer with migration. Generalization of the Yokota–Tanimoto model for any kind of multipole interaction

Two organic sensitisers 4-biphenylcarboxylate (BPC) and terephthalate (TA) were intercalated into the gallery of layered europium hydroxide (LEuH). PL spectra tests indicated that BPC markedly enhanced the red luminescence of Eu(3+) due to efficient energy transfer between BPC and Eu(3+), forming a contrast to intercalated TA and the starting NO(3)(-) anions in the gallery. The energy level matching of the organic guests and Eu(3+) was also discussed to explain the energy transfer from sensitiser to Eu(3+).

/pdf/intercalation-of-organic-sensitisers-into-layered-europium-2pcn0esnyl.pdf

Intercalation of organic sensitisers into layered europium hydroxide and enhanced luminescence property

We present a dynamical model for the rapid change in relative emission from traps and supertraps in molecular solids when the trap concentration is varied. Good agreement between experiment and the theoretical model is obtained in all cases. The physical picture of this model is similar to that of a percolation model and contrasts with the model based on a transition from localized to extended states.

http://web.mit.edu/robertsilbey/research/papers/1971-1980/rsilbey_dyn_approach_exciton_migration_disordered_molec_solids.pdf

Dynamical approach to exciton migration in disordered molecular solidsa)

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Dynamical approach to exciton migration in disordered molecular solidsa)