Amphiphilic copolymers containing 1-(2-naphthyl)ethyl ester groups were prepared and their fluorescence properties were examined. The fluorescence spectra of the copolymers with a higher naphthyl content showed predominantly a broad monomer emission with lambda(max) at 340 nm in methanol, whereas a structured emission with lambda(max) at 344 and 362 nm was observed in aqueous solution. The former spectra changed rapidly to the latter ones upon UV irradiation. Photolysis of the copolymers and the monomeric model compound in methanol gave 2-vinylnaphthalene, whose fluorescence agreed with those of copolymers in water, together with methyl ether, alkylnaphthalenes, and other products. These results indicate that the copolymers hold vinylnaphthalene-like traps, which may emit preferentially in water because of efficient sensitization.