We have monitored in situ the changes that occur in the charge-transfer (CT) emission from the highly fluorescent probe molecule Fluoroprobe (FP) and its fluorogenic derivative Maleimido-Fluoroprobe (MFP) during the radiation-induced polymerization of methyl methacrylate (MMA). While FP remains as a free, fluorescent molecule in the polymerizing medium, MFP is nonfluorescent and displays FP-like fluorescence only when the maleimido group is incorporated into a growing polymer chain to form its copolymerized, succinimido derivative (pMFP). Very abrupt and pronounced changes in both the spectrum and decay kinetics of the fluorescence are found for both probe molecules on traversing the narrow dose region of the gel effect in which the medium suddenly changes from a slightly viscous liquid to a rigid polymeric glass. The two probe molecules display close to identical behavior, apart from a slight indication of preferential concentration of pMTP in polymer-rich and FP in monomer-rich regions of the medium just prior to vitrification. The in situ CT fluorescence spectra and decay kinetics in the fully polymerized PMMA matrix are characteristic of a slightly polar medium with a dielectric constant close to the static value of 3.5 for PMMA. More detailed (ex situ), wavelength-dependent kinetic studies of fully polymerized samples show a bathochromic shift in the fluorescence to occur with a spectral relaxation time of 16 ns for both probe molecules. This is orders of magnitude shorter than the shortest dielectric relaxation time measured in AC studies and is attributed to rapid reorganization of the dipolar side-chain ester groups of the polymer induced by the fully charged donor and acceptor centers in the CT state of the FP chromophore.