Electronic and molecular structures of α,ω-diphenylpolyynes in the lowest excited triplet states

Unusually large |D| values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (|D|=0.396 cm−1) and 1,8-diphenyloctatetrayne (|D|=0.533 cm−1) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T1) states of these diphenylpolyynes were assigned to 3B1u(3πxπ∗x) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T1 states, although the TREPR and phosphorescence spectra indicate interactions between the T1(3πxπ∗x) and Tn(3πxπ∗y) states through spin–orbit and vibronic interactions.