Theoretical studies of relaxation processes in excited state impurity molecules: Application to naphthalene dimers

We present a theoretical study for the relaxation modes of multilevel impurities embedded in a low temperature matrix. The equations of motion for the relevant macrovariables are derived, and the limits of validity carefully delineated. The theory is applied to triplet excitations of naphthalene dimers; the results provide the relations between the microscopic coupling and relaxation mechanisms and the observed spectroscopic data (phosphorescence, EPR, population relaxation, and energy transfer). Comparison is made with relaxation models developed previously, and the limitations of those are discussed.