Effect of the thickness of a dicarbocyanine dye layer on the conformational composition and spatial orientation of layer components

The conformational and aggregate structure and the spatial orientation of polyatomic organic molecules on solid substrates are investigated by the example of molecular layers of symmetric and asymmetric dicarbocyanine dyes. It is shown that the structure of a dicarbocyanine dye layer is determined by two mechanisms: (i) the change in the symmetry of the intramolecular charge distribution in the monomeric components of the layer as a result of the intermolecular interaction with the substrate, which leads to closer values of the equilibrium concentrations of two monomers with different spatial structure (rotational stereoisomers), and (ii) the association of monomer molecules with formation of dimers and J aggregates. The relative position of the spectra of the layer components, the spatial orientation of the components, and the concentration ratio of different monomeric forms depend on the structure and the electron-donating ability of terminal groups. In going from a monomolecular layer to multilayered structures, the asymmetry of the intramolecular charge distribution induced by the substrate and the ratio of different stereoisomeric forms first change and then become stabilized.