Transient resonance Raman spectroscopic and ab initio MO investigation of substituent effects on the T1 triplet states of halobiphenyls

Abstract

Nanosecond transient resonance Raman spectra of the T1 states and Raman spectra of the So states of nine halogenated biphenyl compounds were obtained and ab initio computations were performed to determine the optimized geometry and vibrational wavenumbers of the T1 and S0 states of 10 halogenated biphenyl compounds. Substitution of halogen atoms at meta or para positions relative to the interring C - C bond leads to little change in the structure of the halogenated biphenyl compounds relative to the corresponding So and T1 states of biphenyl. Substitution of halogen atoms at ortho positions results in significant increases in the twisting between the two phenyl rings of the So and T1 states of the halogenated biphenyl compounds relative to the So and T1 states of biphenyl. The degree of twisting between the two phenyl rings in ortho-substituted halogenated biphenyls appears to depend on the steric, electronegativity and/or polarizability properties of the halogen atom. © 2001 John Wiley & Sons, Ltd.