Photocyclization of triphenylamine: an investigation through time-resolved photoacoustic calorimetry

Energetics of formation of the intermediate produced during the photocyclization of triphenylamine (TPA) in alkane and alcoholic solvents have been investigated by employing the time-resolved photoacoustic calorimetric technique. The study, in conjugation with flash photolytic observations, confirms that the long lived intermediate N-phenyldihydrocarbazole (NPDHC) is formed through a cascade of processes. The endothermicity for the process of NPDHC formation from TPA was determined to be ∽53 kcal mol−1 in all the environments studied. The nature and structure of NPDHC have been assigned for the first time. The experimental value of the enthalpy of reaction resembles well that calculated from the semi-empirical (AM1-SCI) method.