A novel method to prepare functional polymer LB films is described. The copolymers of N-dodecylacrylamide with N-acryloxysuccinimide, of which the succinimide moiety is subject to a replacement reaction, form a stable condensed monolayer in a wide range of copolymer compositions. By contact of the monolayer with 1-(1-naphthyl)ethylamine on a water surface, the naphthyl chromophore can be incorporated into the copolymer monolayer by a replacement reaction with a N-hydroxysuccinimide group. The introduction of a large dyestuff, 3-(2＇-aminoethyl)-6-tert-butyl-7-[4＇-[N-ethyl-N-(2-methylsulfonylaminoethyl)amino]2＇-methylphenylimino]pyrazolo[3,2-c][1,2,4]triazole was also succeeded.