LAYERED STRUCTURE OF LANGMUIR-BLODGETT POLYMER-FILMS MEASURED BY INTERLAYER ENERGY-TRANSFER

The layered structure of Langmuir-Blodgett (LB) films of poly(vinyl octal) (PVO) has been investigated by the time-resolved fluorometry of the energy transfer between layers containing energy donor and acceptor moieties. The poly(vinyl octal)s containing phenanthrene and anthracene chromophores (P and A polymers) were synthesized by the acetalization of poly(vinyl alcohol) with octanal and chromophoric aldehyde. The polymer was spread onto pure water and transferred by dipping a quartz plate vertically. The samples (P(n)A), which consisted of two layers of P polymer, n layers of PVO, and two layers of A polymer (n = 0-8) were prepared for fluorescence measurements. The transfer ratio was unity for all the films, and the thickness measured by ellipsometry was proportional to the number of layers. Although the surface film was deposited on the substrate well, energy-transfer efficiency for each P(n)A was larger than the theoretical value predicted by Forster mechanism. This indicates the structural relaxation of the layered polymer films. Assuming Gaussian distribution of the chromophores, the theoretical decay functions for the phenanthrene fluorescence were calculated by the Monte Carlo method according to the Forster mechanism and then were fitted with the observed decay curves. The procedure enabled quantitative evaluation of the partly disordered structure of the polymer LB films. Fluorescence analysis based on the interlayer energy transfer is quite sensitive to microscopic change of the film structure in the molecular dimension.