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 (T-1) states of these diphenylpolyynes were assigned to B-3(1u)((3)pi(x)pi(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 T-1 states, although the TREPR and phosphorescence spectra indicate interactions between the T-1((3)pi(x)pi(x)(*)) and T-n((3)pi(x)pi(y)(*)) states through spin-orbit and vibronic interactions. (C) 1999 Elsevier Science B.V. All rights reserved.