TIME-RESOLVED EPR AND PHOSPHORESCENCE STUDIES OF THE LOWEST EXCITED TRIPLET-STATE OF BENZIL

Time-resolved EPR (TREPR) and phosphorescence studies of the excited triplet states of benzil in various environments are made. On the basis of the TREPR spectral pattern and the phosphorescence peak position (lambda(m)), the T1 state is classified into three types. A clear correlation is found between the zfs and lambda(m) for the T1 states in various environments. This correlation indicates that both the zfs and lambda(m) are determined by the geometry of the T1 state, particularly the dihedral angle (theta) between the two carbonyl groups. A model calculation of the zfs can account for the observed change in terms of the change in theta.