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

Abstract

Nanosecond time-resolved resonance Raman spectra of the T1 states and Raman spectra of the S0 states of 1bromonaphthalene and 1,4-dibromonaphthalene were measured. Ab initio calculations were also performed to determine the optimized geometries and vibrational spectra for the S0 and T1 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 T1 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 T1 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. (C) 2000 John Wiley and Sons, Ltd.