TRANS-STILBENE-AMINE EXCIPLEXES. BEHAVIOR OF THE EXCIPLEX, SOLVENT-SEPARATED RADICAL ION PAIR, AND FREE RADICAL IONS.

Article abstract of DOI:10.1021/ja00315a041

The interaction of singlet trans-stilbene with several trialkylamines and diamines in acetonitrile solution has been investigated by a combination of steady-state measurements and time-resolved resonance Raman spectroscopy. Adduct formation between trans-stilbene and acyclic monoamines is proposed to occur via a short-lived exciplex (contact radical ion pair) intermediate, which is not quenched by ground-state amine. A solvent-separated radical ion pair is formed either directly from an encounter complex or via the exciplex and decays by intersystem crossing to yield triplet trans-stilbene, dissociation to yield free radical ions, or quenching by ground-state amine. Intersystem crossing is more rapid for the diamines vs. monoamines, resulting in a lower yield of free radical ions. Quenching of the solvent-separated radical ion pair by ground-state amine is subject to the same stereoelectronic effect as observed for exciplex quenching in nonpolar solvent.