Absorption and Fluorescence Properties of Rhodamine B Derivatives Forming Langmuir-Blodgett Films

Surface pressurearea isotherms for mixed films of diodadecylrhodamine B and arachidic acid with varying mixing ratios were recorded. Monolayers and multilayers were deposited on hydrophylic glass slides. Absorption spectra, fluorescence spectra, and relative quantum yields of fluorescence were examined as a function of the mixing ratio in the film. The type of aggregates formed in homogeneous solution was not observed, and the relative quantum yield of fluorescence decreases with increasing amount of dye in the layer. From these results a packing in the Langmuir-Blodgett monolayer can be proposed. Two dye molecules form a dimer in which the transition dipoles and the vector linking the centers of the molecules form an angle of 55O, leading to a dimer without spectral shift. The similarity between the photophysical properties of adsorbed rhodamine B molecules at high coverages and of the monolayers investigated in this contribution could point to a similar packing of the hromophores.