Abstract
The ground state conformation, spectroscopy, and photochemical behavior of styrene and eight of its vinyl- and ring-methylated derivatives have been investigated. Introduction of methyl groups at the α-position of the vinyl group or the ortho positions of the phenyl results in increased phenyl-vinyl dihedral angles. Styrenes possessing both α-methyl and ortho-methyl groups adopt orthogonal geometries. Decreased planarity results in a progressive blue-shift in the lowest energy allowed π,π*transition and a decrease in the singlet lifetime. Kinetic modeling of the temperature-dependent singlet lifetimes provides activation parameters for the activated decay pathway, which is assigned to C=C torsion for styrenes with phenyl-vinyl dihedral angles, φ < 60°. Planar styrenes have large torsional barriers (7 ± 1 kcal/mol) and decay predominantly via intersystem crossing and fluorescence at room temperature. Styrenes with values of 30° < φ < 60° have smaller torsional barriers and decay predominantly via C=C torsion at room temperature. Highly nonplanar styrenes decay predominantly via relatively rapid, weakly activated intersystem crossing.
Original language | English (US) |
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Pages (from-to) | 8806-8813 |
Number of pages | 8 |
Journal | Journal of the American Chemical Society |
Volume | 125 |
Issue number | 29 |
DOIs | |
State | Published - Jul 23 2003 |
ASJC Scopus subject areas
- Catalysis
- Chemistry(all)
- Biochemistry
- Colloid and Surface Chemistry