Ultrafast investigations of the photophysics of 4-phenylbenzophenone in solution

Transient absorption experiments were used for ultrafast studies of intramolecular energy transfer in 4-phenylbenzophenone (PBP) in solution. Previous experiments suggested that triplet–triplet energy transfer occurs between the benzophenone and biphenyl chromophores. This mechanism is investigated and a new model involving a phenyl ring isomerization is discussed. The intersystem crossing time is found to be identical within error in benzophenone and PBP. Unlike benzophenone, PBP can undergo a structural change in the excited state which shuts off the intersystem crossing due to the significant decrease in potential energy of the S1 state. This drop in energy also decreases the S1–S0 energy gap, enhancing internal conversion significantly over benzophenone.