A series of reactive (2, 4) and nonreactive (3, 5) fluorescent probes based on 4-(dimethylamino)-4＇-nitrostilbene (1) have been synthesized. Substitution of a methyl on the dimethylamino group results in blue shifts in emission and increases in Phi(f), and corresponding reactive and nonreactive probes are indistinguishable. Emission spectra of 1-5 were recorded during the photoinitiated polymerization of methyl methacrylate (MMA). For nonreactive probes, only minor changes in emission are observed during the first 40% of the reaction, while at conversions between 50 and 90% lambda(max) is proportional to the conversion. For reactive probes shifts of lambda(max) during the early stages of the process are observed, enabling them to monitor the full polymerization process. It was proven that the shift in emission during the first stage of the reaction is due to covalent attachment of the reactive probes to the PMMA backbone.