title: Torsional barriers for planar versus twisted singlet styrenes.
abstract: Kinetic modeling of the temperature-dependent lifetimes of styrene and several methyl-substituted styrenes has been used to obtain the torsional barriers for singlet-state C=C rotation. The barrier for C=C torsion is found to be correlated with the ground-state phenyl-vinyl dihedral angle, varphi, planar styrenes having barriers of approximately 6.5 kcal/mol and moderately twisted styrenes having smaller barriers. Highly twisted styrenes undergo exceptionally rapid intersystem crossing. This unexpected dependence of excited-state behavior on varphi is attributed to a change in the character of the excited states from delocalized for planar styrenes to localized for highly twisted styrenes.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA. lewis@chem.northwestern.edu
authors.forename: Frederick D
authors.initials: FD
authors.lastname: Lewis
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Zuo