FLUORESCENCE QUENCHING BY SINGLET ENERGY TRANSFER .I. FROM BENZENE AND TOLUENE TO PI-BONDED MOLECULES

The rates of intermolecular, electronic energy transfer from the singlet-state benzene and toluene to a variety of π-bonded molecules (CS2, COS, cylic ketones, 4-pentenal, 1,3-pentadienes, 1,3-butadiene, etc.) have been measured. The most efficient quenchers are CS2 and carbonyl compounds, while the conjugated dienes are one order of magnitude less efficient than CS2. Furthermore, the energy transfer to 1,3-butadiene-h6 is about 12% faster than that to 1,3-butadiene-d6, indicating a much smaller deuterium isotope effect than an isotope effect found in the triplet energy transfer from biacetyl to the perhydro- and the perdeuterio-1,3-butadienes. The importance of the overlap between the energy-loss spectrum of the donor and the excitation spectrum of the acceptor for efficient transfer is stressed.