FLUORESCENCE AND ENERGY MIGRATION IN THE RANDOM COPOLYMERS OF (1-NAPHTHYLMETHYL)METHACRYLAMIDE AND SODIUM 2-(ACRYLAMIDO)-2-METHYLPROPANESULFONATE

Random copolymers of (1-naphthylmethyl)methacrylamide (1-NpMAm) and sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with varying compositions were synthesized. Fluorescence spectra of the copolymers in organic solution showed predominant monomer fluorescence of the naphthyl (Np) residues even when the Np content in the copolymers is as high as 58 mol %, unlike conventional random copolymers containing Np moieties. In aqueous solution, by contrast, the copolymers showed a strong preference for excimer emission. The excimer intensity increased with increasing Np content, and the copolymers with > 40 mol % Np content showed almost only excimer emission. The total fluorescence quantum yield increased with increasing Np content, despite an excimer component increase, again unlike conventional random copolymers. The copolymer with 58 mol % Np content showed a rapid decay of Np monomer fluorescence with lifetimes of 28 and 268 ps, which agreed fairly well with the rise times of the excimer (29 and 278 ps) at room temperature. All these findings imply that little or no self-quenching site exists and rapid singlet energy migration occurs solely to preformed excimer sites in the copolymers with a higher Np content in aqueous solution. Efficient triplet energy migration was also observed for the copolymers in aqueous rigid solution at 77 K.