STRUCTURES AND DYNAMICS OF THE LOWEST EXCITED TRIPLET-STATE, RADICAL-CATION AND RADICAL-ANION OF 1,4-DIPHENYLBUTADIYNE - TIME-RESOLVED RESONANCE RAMAN-STUDY

Time-resolved resonance Raman spectra of the lowest excited triplet st ate T-1, the radical cation R(.+) and the radical anion R(.-) of 1,4-d iphenylbutadiyne (DPB) have been measured. It has been shown that the C=C symmetric stretch exhibits low-frequency shifts in the order, S-0 (2219 cm(-1)), R(.+) (2156 cm(-1)), R(.-) (2108 cm(-1)), and T-1 (1999 cm(-1)), indicating that the C=C triple bond weakens in this sequence . However, the frequency shifts are not as large as those observed for diphenylacetylene (DPA), suggesting that in the case of DPB the unpai red electron (spin density) is distributed over the two C=C triple bon ds of the conjugated system, which makes the weakening of the C=C bond s of DPB much less than that of DPA. It has also been shown that like DPA, the ionization of DPB to generate R(.+) can occur biphotonically through the T-1 state.