Photoinduced Picosecond Bimolecular Reaction between trans-Stilbene and Carbon Tetrachloride

A new photochemical reaction has been found between trans-stilbene and carbon tetrachloride. In carbon tetrachloride, the first excited singlet (S1) state of trans-stilbene decays with a time constant of 3.1 ± 0.2 ps, a factor of ten or more faster than in alcohols and hydrocarbons. The mechanism of this anomalous lifetime shortening has been studied by using four time-resolved spectroscopies: sub-microsecond infrared, picosecond Raman, sub-picosecond visible absorption, and picosecond fluorescence. After photoexcitation to the S1 state, a bimolecular reaction occurs between trans-stilbene and the solvent carbon tetrachloride to form a stilbene-Cl adduct and the trichloromethyl (·CCl3) radical. Then, the stilbene-Cl adduct and the ·CCl3 radical are likely to react further in about 100 μs, following second-order reaction kinetics. The newly found photochemical reaction between trans-stilbene and carbon tetrachloride can serve well as a prototype for studying the microscopic mechanism of bimolecular reactions in solution.