Absorption Spectra and Molecular Arrangement of Mixed Aggregates in LB-films: Separated, Amalgamated, Persistent and Mosaic Types

摘要

The molecular monolayer assemblies incorporating the aggregates of two kinds of cyanine dyes are interesting as a model of mixed molecular clusters, which afford a possibility to create spectral sensitizers for imaging materials with controlled optical density and spectra in the wide wavelength range. Two dyes with a similar molecular structure may form positionally disordered aggregates of different types: amalgamated and persistent ones. On the other hand, dissimilar dye combinations would give rise to a separated-type aggregate. Intermediate case would be a mosaic-type aggregate. The arrangement of molecules and their parameters (monomer wavelength, transition dipole moment, dipole orientation, disorder) define the positions, line shapes and magnitude of absorption peaks. In this paper, we present numerical quantum mechanical calculations of the absorption spectra of 2D-aggregates of different types. By fitting the calculated spectra with experimental ones, we have obtained possible molecular arrangements, consistently giving good agreement for a wide variety of molar fractions of the mixture.