Mechanism Switching and Trapping of Triplet-Triplet Energy Transfer in an Orientationally Disordered Molecular Solid.

摘要

The separation between the ions or molecules in disordered solids varies at random. The optical transition energy could also vary over a wide range for the different molecules or ions in the solid resulting in a large inhomogeneous line width (delta v inh). This allows energy transfer and spectral diffusion studies to be carried out between the same chemical species but at different local environments in these solids using lasers for excitation. Furthermore, when carried out at temperatures at which kT delta v inh, energy transfer becomes unidirectional, i.e., to molecules or ions having transition energies equal or lower than the laser-excited-donors within the inhomogeneous profile. This allows studies on the dependence of the rate and mechanism of the energy transfer on the acceptor concentration (i.e., on donor-acceptor separation) to be carried out by simply changing the laser wavelength within the inhomogeneous profile. By analyzing the temporal behavior of the emission intensity of the pulsed-laser-excited set of molecules or ions (donors), the mechanism of the excitation transfer can be elucidated. These types of studies are carried out on the triplet-triplet energy transfer in a unique type of disordered solid, orientationally disordered molecular solids, e.g., 1-bromo,4-chloronaphthalen (BCN) neat solid.