EXCIMER FORMATION AND ENERGY TRAPPING IN LANGMUIR-BLODGETT-FILMS OF POLY(VINYL OCTAL) CONTAINING PYRENE CHROMOPHORE

Mono- and multilayered films of poly(vinyl octal) containing pyrene chromophore have been prepared by the Langmuir-Blodgett (LB) technique. The photophysical processes, excimer formation and energy trapping of pyrene chromophore in the 2-dimensional and quasi 3-dimensional systems, have been investigated by photostationary and time-resolved fluorescence spectroscopy. Monolayered films of the polymer on pure water were transferred to a quartz plate at 19 °C as a Y-type film. UV absorbance and fluorescence intensity of the built-up films were proportional to the number of layers. The obtained films show little excimer emission. The ratio of excimer fluorescence to the monomer fluorescence is much less than that of mixed films fabricated from a conventional fatty acid with pyrene chromophore, at the same concentration of the chromophore in a plane. Fluorescence decay analysis by a 2-dimensional energy-transfer model gives the density of excimer-forming sites. The results indicate that the polymer LB films attain a statistically uniform distribution of pyrene moieties. In multilayered films, the decay curves did not fit to the Förster kinetics in which energy migration is not involved, and they were analyzed by the Yokota-Tanimoto Padé model involving migration of the excited state among pyrene moieties. The diffusion coefficient for the energy migration was found to be 1 × 10−8 cm2 s−1. The observed characteristics of the polymer LB films are attributed to the uniform distribution of pyrene moieties and the thin thickness of each layer. © 1990, American Chemical Society. All rights reserved.