Molecular organization of perylene derivatives in Langmuir-Blodgett multilayers

In this work we discuss molecular organization and spectroscopic properties of Langmuir-Blodgett multilayers of two fluorescent perylenetetracarboxylic acid derivatives and their mixtures with fatty acid. A single component and mixed films were formed on pure water surface and deposited onto solid substrate by multiple vertical substrate immersion. After the deposition spectroscopic properties of the multilayers were studied. The X-ray diffraction profiles show periodical structures with the period of 1.5 nm of the multilayer pure dye films deposited onto gold covered glass substrates. The optical spectroscopy analysis shows that perylene dye molecules are present in monomer and aggregated forms in both types of the films, which is revealed by the absorption and fluorescence spectra as well as two-exponential decay of fluorescence. The morphology of the films in the nanoscopic scale was examined using atomic force microscopy. The LB film topography made of the dye with shorter alkyl chain substituent revealed emergence of belt-like aggregates, whereas in the case of the dye with longer alkyl chain substituent columnar structure was observed. Our results show that the dye aggregation in the LB multilayer systems is not the same as in single LB layers.