Triplet-triplet absorption of biphenyl

Biphenyl in a cooled alcoholic solution shows structured TT absorption bands, weak in the visible and strong in the UV with a maximum at 3700 angstrom and en epsilon(tau) = 50 000 litre mole(-1) cm(-1). Calculations using the PPP SCF method with a large configuration interaction are done using a planar model. The influence of the extension of the configuration interaction and of the planarity of the molecule in the triplet state on the calculated energies and oscillator strengths are tested. The bends are tentatively assigned to the week B-3g(-) <- B-1u(+) and A(g)(+) <- B-1u(+) and the strong A(g)(-) <- B-1u(+) transitions.