Nanosecond time-resolved resonance Raman spectroscopic and ab initio MO investigation of substituent effects on the triplet states of bromonaphthalenes

Nanosecond time-resolved resonance Raman spectra of the T-1 states and Raman spectra of the S-0 states of 1-bromonaphthalene and 1,4-dibromonaphthalene were measured. Ab initio calculations were also performed to determine the optimized geometries and vibrational spectra for the S-0 and T-1 states of 1-bromonaphthalene and 1,4-dibromonaphthalene were predicted, The results were compared with those previously found for 2-bromonaphthalene and it was found that the Br atom substitution position and number both affect the changes in the C-Br bond in the T-1 and T-n states. The intensities of the time-resolved resonance Raman spectra indicate that the C-Br bond changes its structure much more in the T-n state relative to the T-1 state of 2-bromonaphthalene than 1-bromonaphthalene or 1,4-dibromonaphthalene. Possible implications of these substitution position effects on the 'reluctant' bond cleavage processes occurring from the T-n states of bromonaphthalenes are discussed. Copyright (C) 2000 John Whey & Sons, Ltd.