Spectroscopic and AFM Study of Unsymmetrical Diester of Perylene-3,4,9,10-Tetracarboxylic Acid in Monolayers Formed by Means of Langmuir-Blodgett Technique

The synthesis of perylene monoimide dye and the ability of Langmuir and Langmuir-Blodgett (LB) films formation are reported. The perylene-like dye - n-butyl diester of N-(n-octyl)imide of perylene-3,4,9,10-tetracarboxylic acid and arachidic acid (AA) or thermotropic liquid crystal 4-octyl-4'-cyanobiphenyl (8CB) were used to compose mixtures of different mole fraction. The electronic absorption and emission spectra of the dye in diluted chloroform solution, a 10 mu m thick liquid crystal sandwich cell, in the monomolecular film on water surface (in situ) and after deposition on quartz substrates were recorded. In the Langmuir and LB films the dye molecules reveal tendency to creation of self-aggregates what is reviled by significant broadening of the absorbance bands and changes in emission spectra. It has been shown that the molecules of the perylene dye under investigation exhibit a strong tendency to create H-types of aggregates in highly concentrated LB films. The emission spectra show the genuine excimer emission of the dye in the LB films. The AFM surface image of the pure dye monolayer showed that molecules form a two-level film with height of about 0.6 nm and 2.5 nm. Topographies of mixed monolayers with arachidic acid revealed three-level structures with circular domains of AA within the dye monolayer. From the highest analyses, a partial miscibility of the dye with arachidic acid (AA) is postulated.