Evidence for Triplet Exciplex Formation in the Reaction of Amines

l-Phenyl-2-acetoxy-2-methylpropanone-l has been irradiated with 25ns flashes of 347 nm light in benzene or cyclohexane solution. Absorption measurements yielded the following: at the end of the flash the triplet-triplet spectrum was observed (triplet decay rate constant: &t = (3.0 ±0.2) 105 s i). In the presence of aliphatic amines (e.g. triethanol amine) radicals were formed much more slowly than triplets disappeared, as clearly indicated by spectral changes at wave lengths between 330 and 380 nm. The radical precursor thus evidenced is presumed to be an exciplex. Rate constants: + amine: (1.2 + 0.2) 109 1/mol s; /."exciplex: ( 9 ± 1) 106 s 1 .