EXCIPLEX EMISSION AND PHOTOFRAGMENTATION REACTIONS OF CONTACT ION-PAIRS GENERATED VIA QUENCHING OF CYANOAROMATIC SINGLETS BY AMINO-ALCOHOLS

Intermolecular quenching of singlet cyanoaromatics by 1,2-amino alcohols in nonpolar solvents results in an oxidative fragmentation of the amino alcohol donor concurrent with two-electron reduction of the cyanoaromatic. In several cases the reactive pairs exhibit weak exciplex fluorescence which can be closely correlated with the fragmentation; the attenuation of exciplex fluorescence as well as the photofragmentation as solvent polarity is increased for the intermolecular reaction indicates that a contact ion pair exciplex is the reactive intermediate. Molecules containing both an electron acceptor and an amino alcohol exhibit strong exciplex fluorescence and enhanced photofragmentation efficiencies in nonpolar solvents; both exciplex fluorescence and fragmentation persist in these cases as solvent polarity increases. An increase in fragmentation and decrease in fluorescence yields is observed as solvent polarity or base strength is increased, again indicating that the reactive state is an emissive ion-pair exciplex.