Singlet-triplet interconversion of diphenylmethylene. Energetics,dynamics and reactivities of different spin states

A combination of picosecond and nanosecond laser spectroscopy measurements, chemical quenching experiments and triplet sensitization experiments has allowed the determination of the rapid singlet to triplet and slower triplet to singlet intersystem crossing rates for diphenylmethylene in fluid solution at room temperature. It is shown that under the conditions of the kinetic measurements, singlet and triplet diphenylmethylene (¹DPM and ³DPM, respectively) are in rapid equilibrium relative to reactions, so that knowledge of the values of k_ST and k_TS allows determination of the equilibrium constant and change in free energy for the ¹DPM 〈 ³DPM process. The absolute reactivity of ¹DPM toward a series of alcohols has been determined and is discussed in terms of other current investigations of carbene reactivity.