HIGH POLARITON REFLECTANCE IN HEPTAMETHINEBIS-(DIMETHYLAMINO)CYANINE CHLORIDE CRYSTAL

The reflection spectra of single crystals of bis(dimethylamino)heptamethinium chloride were measured with polarized light in the region from 500 to 38000 cm-1. The Kramers Kronig transformation was calculated and the determined dielectric functions are discussed in terms of the polariton and molecular exciton theories. The highly anisotropic reflection band is caused by one narrow molecular transition, which is polarized parallel to the molecular chain. The bathochromic shift of the transition energy compared to the value in solution and the large splitting of transverse and longitudinal modes are explained by the molecular exciton theory. The expected charge resonance transition could not be found. That will be discussed in respect to the arrangement of the molecules in the crystal.