Amine dimer cation radical formation upon quenching of trans-stilbene-amine exciplexes by amines

The interaction of singlet trans-stilbene with trialkylamines in benzene solution yields fluorescent exciplexes for which the predominant decay pathway is intersystem crossing to yield triplet trans-stilbene. Both the fluorescence and intersystem crossing processes can be quenched by added tertiary and primary amines. Exciplex quenching is subject to a pronounced steric effect, being inhibited by both N and α-C alkylation. Intramolecular exciplex quenching by the free amino group of α,ω-alkanediamines is highly dependent upon the diamine chain length. The observed steric and chain length effects on exciplex quenching are indicative of the formation of a triplex of trans-stilbene anion radical and a σ-bonded amine dimer cation radical.