Quenching of dual fluorescences of pyrene vapor by high-pressure oxygen or nitric oxide

Abstract

Quenching of dual fluorescence emissions (S 1 - and S 2-fluorescence) of pyrene- h 10 and pyrene- d 10 by oxygen or nitric oxide in the vapor phase at 170°C has been investigated over a wide range of the quencher pressure up to 1000 torr. In addition to slow emission, the S 2-fluorescence contains a small amount of fast emission which is not quenched even at the highest pressure of quenching gas. From the change of the ratio between the S 1 - and S 2-fluorescence quantum yields with the pressure of the quenching gas, the rate constant of the forward internal conversion S 2 ▪ S 1 is found to be ≈ 3 × 10 13 s −1 regardless of excitation energy, while that of the reverse internal conversion S 2 ▪ S 1 is found to change from 1 × 10 9 to 3 × 10 10 s −1 on increasing the excitation energy from 33.6 × 10 3 to 42.7 × 10 3 cm −1. The quantum yield of the fast S 2-fluorescence is evaluated to be about 5 × 10 −6 irrespective of excitation energy.