The performance of a series of phthalimide derivatives as fl uorescent probes for moni- toring of cationic photopolymerization of monomers by Fluorescence Probe Technology (FPT) has been studied in comparison to the performance of a 7-diethylamino-4- methylcoumarin (Coumarin 1) probe. It was found that the phthalimide probes are much more stable than Coumarin 1 under cationic polymerization conditions. Moreover, the aminophthalimide probes turned out to be long-wavelength sensitizers for the dia- ryliodonium photoinitiators used to initiate the polymerization process. The sensitizing effect of the probes compensates in excess the inhibiting effect of their amino groups on the cationic polymerization kinetics.