Fluorescence Energy Transfer and Oxygen Quenching in Solutions of Diphenyloxazole in Cyclohexane

The fluorescent intensity of solutions of diphenyloxazole (PPO) in cyclohexane is measured as a function of concentration for excitation by γ rays. The fluorescence spectrum of the solutions when excited by uv is also recorded. These uv measurements, together with the results of β excitation, were used to examine the quenching influence of oxygen on the solute fluorescence and on the energy transfer from cyclohexane. The decay times of the solutions are measured. The results are interpreted to show: (1) a tendency of PPO to form molecular complexes in cyclohexane and (2) a ``static'' character for the oxygen quenching of cyclohexane. The dependence of transfer probability on solute concentration is discussed.