Mechanism of interaction of coumarin-based fluorescent molecular probes with polymerizing medium during free radical polymerization of a monomer

The effect of an electron-donating and an electron-withdrawing substituent at 4-position and selected electron-donating substituents at the 7-position of coumarin structure on its ability to monitor free radical photopolymerization of diethylene glycol dimethacrylate by the Fluorescence Probe Technique (FPT) has been evaluated. It was found that the fluorescence spectra position of the probes studied depends only on changes of the medium polarity and is not sensitive to changes of microviscosity. The changes of microviscosity of the medium upon monomer polymerization can be monitored only with probes that have fluorescence in liquid monomer partially quenched by the substituents, using relative fluorescence intensity measured at peak maximum. Mechanism of how the probes work has been discussed. Moreover, photostability of the probes studied under free radical photopolymerization conditions has been evaluated and the factors affecting the photostability have been suggested. 7-Amino-4-trifluoromethylcoumarin was found to be the most sensitive and photostable probe under the conditions studied.