INTERACTION OF PHOTOEXCITED NAPHTHALENES WITH TRIFLUOROACETIC-ACID

The bimolecular hydrogen-exchange reaction of naphthalene with trifluoroacetic acid involves the singlet excited state of the hydrocarbon. Comparison of the efficiency of fluorescence quenching of naphthalene by trifluoroacetic acid with the effect of the acid in promoting hydrogen exchange indicates that the initial interaction of trifluoroacetic acid with excited naphthalene affords a π complex, which is 100 times more likely to collapse to ground-state reactants than to proceed to isotopically exchanged products. The trifluoroacetic acid assisted photodecomposition of 1-chloronaphthaiene is also a singlet state reaction. It is believed to involve protonation of the excited halide, followed by electron transfer from the solvent, ether. Support for this mechanismwas obtained by showing that other solvents whose ionization potentials are comparable with that of ether promote similar photochemistry. © 1979, American Chemical Society. All rights reserved.