INTERLAYER ENERGY-TRANSPORT IN LANGMUIR-BLODGETT POLYMER-FILMS OF POLY[2-(9-CARBAZOLYL)ETHYL METHACRYLATE-CO-ISOBUTYL METHACRYLATE]

Excitation energy transport through an ultrathin film has been investigated with a designed structure of copolymers containing carbazole and anthracene chromophores. Poly(isobutyl methacrylate) gives a stable monolayer at the air-water interface, and it is transferrable to a solid substrate. Various kinds of chromophores can be incorporated into this monolayer in the form of methacrylate esters. Using the Langmuir-Blodgett (LB) technique with these copolymers, artificial arrangements of the chromophoric units can be realized in a layered structure of the LB film. The carbazole chromophore exhibited simple monomer emission, and no excimer was detected. This spectroscopic property enabled us to carry out quantitative analyses of the interlayer energy-transfer process. Time-resolved fluorescence spectroscopy clearly showed efficient energy migration among carbazole chromophores. After several steps of interlayer migration, the excitation energy transfers to the anthracene layer coated on the carbazole layers. Although some unknown traps exist in this LB film, statistically random distribution of both the donor and acceptor moieties in each layer results in a high quenching yield of the carbazole excitons. Besides the uniform distribution, an advantage of polymer LB films is the thinness of each layer. These properties make possible the efficient energy transport through the layered structure.