Applying time-resolved laser (337 nm) spectroscopy, we have analysed the photochemical and photophysical behaviour of N,N-dimethyl-4-nitroaniline (DMNA) and its dependence on the irradiation time and the presence of N,N-dimethylaniline (DMA), as reducting agent, and lauryl acrylate (LA) monomer, under aerobic and anaerobic conditions. The laser-induced phosphorescence of the initiator is efficiently quenched by DMA inducing the appearance of new emissions as a result of radiationless processes. The spectral and temporal characteristics of these new bands together with their dependence on both the laser intensity and irradiation time allowed their assignment and provided evidence for the photosensitization process of DMA from the excited initiator to be the main photoinitiation mechanism of polymerization.