Quenching of singlet 9,10-dicyanoanthracene by cis- or trans-stilbene in acetonitrile solution leads to a steady-state mixture consisting of 98.8% trans- and 1.2% cis-stilbene. Quantum yields for isomerization of cis-stilbene increase with increasing stilbene concentration, solvent polarity, salt concentration, and decreasing light intensity. These effects are attributed to a cation radical chain process in which the cis-stilbene cation radical isomerizes to the more stable trans-stilbene cation radical, which undergoes electron hole transfer to neutral cis-stilbene in competition with back electron transfer to the dicyanoanthracene anion radical. One-electron oxidation of cis-stilbene substantially lowers the activation energy for isomerization. In the presence of oxygen, the cation radical isomerization mechanism is suppressed and photooxygenation of cis- and trans-stilbene occurs.
ASJC Scopus subject areas
- Colloid and Surface Chemistry