Self-quenching and electronic energy transfer of triplet molecules. The benzaldehyde-biacetyl system in the vapor phase

Abstract

The triplet-triplet energy transfer from benzaldehyde to biacetyl and the competing self-quenching between triplets and ground state molecules of benzaldehyde were investigated in the dilute vapor phase by monitoring the phosphorescence (T1(nπ*)So) decay of benzaldehyde. Following excitation into the S1(nπ*)S0 absorption band, a triplet self-quenching rate constant of kSQ=(2.4±0.1) × 104 s−1 Torr−1, corresponding to a gas-kinetic cross section of σSQ=0.22 A2, was measured. The collision-free lifetime of the benzaldehyde triplet was found to be 2.3 ± 0.4 ms. Substitution of the aldehydic proton by deuterium reduces kSQ by a factor of two: complete deuteration of the molecule has no further effect. Under the same excitation conditions, the energy transfer rate to biacetyl is kET=(2.8 ± 0.1) × 106 s−1 Torr−1, with σET = 24 A2. This process is not influenced by deuteration.