N,N'-5-(2-benzimidazolyl)-1,3-phenylenebis(methacrylamide) (BIPBMA) was synthesized and copolymerized with methyl methacrylate (MMA) by changing feed BIPBMA/MMA molar ratio. The swelling experiments suggest that these cross-linked copolymers (c-copolymers) have a polymer network structure. To compare with c-copolymers, synthesized 3-(2-benzimidazolyl) phenylmethacrylamide (BIPMA) was copolymerized with MMA by changing feed BIPMA/MMA molar ratio. These linear copolymers (l-copolymers) were dissolved in N,N-dimethylacetamide (DMA). The fluorescence spectra of c-copolymers were well fitted by trial-and-error contraction with sums of five or less of Lorentzian equations. The fluorescence spectra of l-copolymers were so distributed that only the initial peak was fitted to a single Lorentzian equation. The fluorescence spectra of BIPBMA/DMA solutions with various concentrations were also fitted to sums of five or less of Lorentzian equations. The fitted coefficients were used to quantify dilution effect. The fluorescence intensity of c-copolymers is higher than that of l-copolymers in a same chromophore concentration. A relation between the intensity and the chromophore concentration shows a concentration quenching owing to chromophore aggregating for c-copolymer, l-copolymer, and the solution. A critical concentration point before which the intensity increases appeared in the plots of intensity against concentration for the c-copolymer and the solution. The critical point of the c-copolymer is higher than that of the solution and that of the l-copolymer (if observed). This suggests that the network formation and the dilution break up the chromophore aggregates. The fluorescence spectra of c-copolymers (1/200) adjusted by varying AIBN concentrations suggest that the fluorescence is independent of the extent of cross-linking. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1841-1845, 2010