Effects of dilution with PMMA and network formation on fluorescence from benzimidazolylphenylenes linked to PMMA network

Abstract

AbstractN,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. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010