Electronic properties of aromatic hydrocarbons II. Fluorescence transfer in solid solutions

The fluorescence of solid solutions of aromatic hydrocarbons has been investigated with the object of studying the transfer of excitation energy from solvent to impurity. Anthracene and pyrene were used as solvents, and the solutes comprised nine larger condensed hydrocarbons. The concentration ranged from 10-5 to 10-1M. Fluorescence spectra were observed by photographic spectrophotometry, and the degree of quenching and quantum efficiency of the transfer process were obtained by comparison with the pure solvent. The dependence of quenching on concentration of impurity may be deduced from a simple theory of exciton migration. The experimental results are in good agreement with this model. The efficiency of a particular impurity species in capturing the excitation cannot be predicted on any simple basis, but there is some evidence that it depends on the symmetry properties of the excited states of solvent and impurity. It is not directly determined by the overlap of solvent emission and impurity absorption, as is the case with sensitized fluorescence.