Properties and the nature of electric-field-induced variations in optical absorption spectra of polymethine dyes in polymer matrices

The effect of a permanent electric field on the absorption spectra of ionic (cationic and anionic) and intraionic symmetric and asymmetric polymethine dyes in poly-N-epoxypropylcarbazole, polyvinylbutyral, and polystyrene pol ymer films is studied. It is found that the electric field causes an increa se in absorption of symmetric dyes in the short-wavelength region and a dec rease in their absorption in the long-wavelength region. Asymmetric dyes ex hibit opposite properties. These properties are common for these groups of dyes irrespective of their chemical structure and ionic nature. They are re tained both in photoconducting polymers and in polymers that are incapable of charge photogeneration. These effects also take place in liquid solution s, although in this case they are much weaker. Various mechanisms of the in fluence of an electric field on the spectral such as the electron transfer, Stark and Kerr effects, intermolecular interactions, and dye isomerization , are discussed. It is shown that the spectral effects are caused by the re distribution of the electron density in a chromophore of the dye in the gro und state resulting in a change in the probability of vibronic transitions. (C) 2001 MAIK "Nauka/Interperiodica".