Knowledge Bank

Polarized absorption measurements have been made on benzophenone and substituted benzophenones of know crystal structure. It has been shown conclusively that the singlet $n\to \pi \ast$ transition in benzophenone is polarized parallel to the carbonyl direction, whereas in the case of 4,4-dimethoxybenzophenone the transition is polarized perpendicular to the carbonyl direction. The polarization of the singlet triplet transitions in these molecules has also been determined. The symmetries and structures of the singlet and triplet $n\pi \ast$ states will be discussed, as well as the vibronic nature of the transitions that are manifest in the low temperature spectra.