SPECTRAL PROPERTIES OF BACTERIOCHLOROPHYLL-C IN NEMATIC LIQUID-CRYSTAL .1. MONOMERIC FORMS OF DYE

The spectroscopic features of bacteriochlorophyll c and bacteriopheoph ytin c in a nematic liquid crystal matrix have been investigated. Abso rption, circular dichroism, fluorescence and time resolved delayed lum inescence spectra have been measured. The pigment is introduced to the liquid crystal from a dry and from a hydrated chloroform solution. In both cases the pigment is in the monomeric form. Hydration of the sol vent and the presence or absence of the central Mg atom affect the int eraction of the pigment molecules with the liquid crystal matrix, chan ging the fluorescence anisotropy. A model for the bacteriochlorophyll c orientation in the liquid crystal is proposed and the averaged angle s between the transition moments and the liquid crystal orientation ax is are determined. A slow process (in the microsecond range) of radiat ive deactivation of energy absorbed by the pigments is observed. This delayed emission could be due to pigment ionization and delayed charge recombination and/or thermal activation from the triplet to the excit ed singlet state.