Alternating copolymers containing an aromatic chromophore in every monomer unit 3. Intramolecular excimer formation and energy transfer in poly(1-naphthylmethyl methacrylate-alt-2-vinylnaphthalene)

Alternating and random copolymers of 1-naphthylmethyl methacrylates (1NpMMA) and/or 2-vinylnaphthalene (VNp) were synthesized, and their fluorescence properties compared in tetrahydrofuran (THF) or 1,4-dioxane. The alternating copolymer of 1NpMMA and styrene (a-1NpSt) was found to form an excimer as freely as the corresponding random copolymer, and poly(1NpMMA-alt-VNp) (a-1NpVNp) also showed an excimer emission, indicating that excimer formation between the naphthyl (Np) chromophores in the alternating methacrylate sequences cannot be inhibited. The observation of monomer emission for 1NpVNp-type copolymers suggests that energy transfer occurs favourably from the 1NpMMA units to the VNp ones at room temperature, and that the transfer in the opposite direction, i.e., the transfer from the VNp units to the 1NpMMA ones, is possible at higher temperatures. The fluorescence-quenching study, however, showed no enhancement of the quenching efficiency for a-1NpVNp at room temperature. The predominant one-way energy transfer might not facilitate the long-range energy migration along the polymer chain.