Photocyclization of Diphenylamine Studied by Time-Resolved Thermal Lensing. Heat of Reaction, Energetics, and Reactivity of Intermediates

Article abstract of DOI:10.1246/bcsj.65.1084

The time-resolved thermal lensing (TRTL) technique was employed to study the photocyclization of diphenylamine (DPA) to form intermediate 4a,4b-dihydrocarbazole (DHC) in methanol solution at room temperature.The heat of reaction, ΔH, was determined to be (2.6+/-0.2)*10² kJmol^-1 (¹DPA -> ¹DHC): The reaction proceeds endothermically.The ring closure step proceeds on the triplet surface (³DPA^* -> ³DHC^*).These triplet states are found to be isoenergetic by analyzing the time evolution of the TRTL signal. ³DHC^* is located at 21 kJmol^-1 above ¹DHC.Furthermore, two-color laser flash photolysis experiments have revealed that the photoexcitation of intermediate ¹DHC leads to the recovery of parent DPA and therefore inhibits the formation of carbazole.