Three-component photoinitiators comprised of an N-arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron-deficient N-arylphthalimide resulted in a greater acrylate polymerization rate than an electron-rich N-arylphthalimide. Triplet energies of each N-arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N-arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron-proton transfer from an intermediate radical species to the N-arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. (C) 2004 Wiley Periodicals, Inc.