Influence of Molecule-Substrate Interaction on Component Composition of Cyanine Thin Films

It was found that the absorption spectra of thin films of cyanine molecules are considerably broader than spectra of their solutions. This is because the equilibrium solutions of molecules contain all-trans isomers as major component, whereas their layers contain several monomeric (all-trans and cis isomers) and associated (dimers and J aggregates) components. Presence of molecular components in layer depends on the electron-donor ability of end groups and surface molecular concentration. The asymmetry in the electron density distribution along conjugated chain affects the equilibrium concentration of isomers in a molecular layer.