A simple method for the fabrication of ultrathin films containing low molecular weight dye material is introduced(post-adsorption technique). The chromophore used is 4-nitro-4'-decyloxy azobenzene quaternary ammonium salt (azo-10Q).In classical layer-by-layer (LBL) procedures

where the substrate is dipped alternately into the chromophore solution and thecomplementary polyelectrolyte

the chromophore tends to desorb from the film during subsequent immersion in thepolyanion solution

and there is little or no indication of multilayer growth.The extent of desorption depends somewhat on the selection of polyelectrolyte

the ionic strength and the pH of solution.An alternative approach is to first prepare conventional LBL films from a pair of oppositely charged polyelectrolytes

and then to soak this film into the chromophore solution

where adsorption by penetration into the LBL film may take place.In preliminary results

a linear dependence of UV absorbance on layer number of LBL film thus prepared was found

demonstrating the apparent effectiveness of the post-adsorption technique for the preparation of azo-10Q-containing ultrathin films.