Vibrational and electronic infrared absorption spectra of benzophenone in the lowest excited triplet state

Time-resolved infrared absorption spectra of photoexcited benzophenone (BP) in carbon tetrachloride and benzene were measured with the use of a dispersive nanosecond time-resolved infrared spectrometer. The vibrational infrared spectrum of BP in the n–π* T1 state (T1 BP) was obtained. The CO stretch mode of T1 BP was not observed in contrast to the transient Raman spectra reported previously. In addition, a broad electronic absorption band ascribable to the T2 ← T1 transition was observed in the wavenumber region higher than ∼2000 cm−1. Those results indicate that time-resolved infrared spectroscopy is powerful not only for observing vibrational transitions in an excited electronic state but also for examining transitions among closely lying excited electronic states of conjugated molecular systems.