Excitation dynamics of fluorescent probes in polystyrene thin and ultrathin films

Fluorescence dynamics of 6-(N-(7-nitrobenz-2-oxa-1,3-dazo1-4-y1)amino) hexanoic acid(NBD) was used to probe molecular motion in polystyrene (PS) thin and ultrathin films. NBD was tagged to phenyl group of PS with the concentration of 1.3 × 10^-2 mol %. Polymer films with various thicknesses were prepared onto quartz plates by a spin-coating method. Excitation light with the wavelength of 435 nm was irradiated onto the films, and the fluorescence was observed by a spectrometer. Fluorescence intensity per unit thickness (I_u) decreased with decreasing thickness. Since I_uis closely related to fluorescence quantum yield, the result indicates that the quantum yield in the film decreased with decreasing thickness. Based on the analysis using a model composed of surface, bulk and interfacial layers, I _u of the surface and interface layers was claimed to be smaller and larger than the bulk value, respectively. This implies that local free volume and/or molecular motion with a relatively small scale at the surface and interface are/is different from those/that in the bulk. The detailed discussion will be presented in a poster.