Investigation of the interaction of macromolecules of semiconductor polymers and cyanine dye

Abstract

In the article the results of experimental and quantum-chemical study of a composite based on a photoconductive polymer and a cyanine dye are presented. The absorption and fluorescence spectra of the dye were studied experimentally. The results showed that the spectra of the cyanine dye in the polymer matrix are batochromatically shifted with respect to the absorption and fluorescence spectra of the dye in the solution. The broadening of the dye spectra, as well as their shift, is associated with a more dense packing of molecules in solid films. As a result, the forces of intermolecular interaction of the dye molecules increase,
which is manifested in a decrease in the energy of the electronically excited state of the dye. Through the comprehensive analysis of spectral data and quantum chemical calculations, the most optimal configuration and optical properties of the dye and polymer molecules are predicted. It was found that the conformation of the «sandwich» with the distance between interacting molecules equal to 2.2–2.4 Å is the most optimal. The calculations showed that in the complexes of the cyanine dye and photoconductive polymer the delocalization of the electron density, as well as a change of the dipole moment of the transition occurs. In this case, the energy of the S₀-S₁ transition is decreased and the intensity of the short-wave absorption is increased, which is proportional to the oscillator strength for the transition. The contribution coefficient of the HOMO-LUMO molecular orbitals in the studied complexes is quite large. The obtained results can be used to create systems with predictable properties.