ELECTRON-TRANSFER QUENCHING ACCOMPANIED BY HIGHLY EFFICIENT ENERGY MIGRATION IN POLYMER LANGMUIR-BLODGETT-FILMS

Copolymers of N-dodecylacrylamide (DDA), which has the excellent property to form LB film, and 2-(9-carbazolyl)ethyl acrylate (CzEA) with various copolymer compositions were prepared to investigate the electron transfer quenching of the excited carbazole chromophore in LB film assembly. The copolymers form a stable condensed monolayer and LB film in a wide range of copolymer compositions. In LB films, the emission spectra show only the structured emission characteristic of the monomeric carbazole chromophore at 350 nm and no excimer emission whereas the corresponding N-vinylcarbazole copolymer LB films in the previous study show strong emission from excimer which acts as an energy trapping site. For the quenching study, the DDA-CzEA monolayer are in direct contact with the mixed monolayer of barius stearate and stearyl viologen quencher. The emission of the excited carbazole was quenched effectively by a small amount of the viologen quencher in the mixed monolayer. The quenching efficiency was varied linearly by the mole fraction of carbazole chromophore in the copolymer monolayer. The effective electron-transfer quenching is attributed to the highly efficient energy migration between carbazole chromophores, which is assisted with a regular alignment of carbazole chromophore and no excimer formation in the copolymer LB films. The plots of (I-0/I - 1) (I in the presence of and I-0 in the absence of the quencher) vs distance (R) between the quenchers gave a linear relationship. The mechanism of electron transfer quenching in the LB film assembly is discussed on the basis of electron-tunneling and energy migration.