Polarized Absorption and Emission of Chlorophyllin, Phycoerythrobilin and Phycocyanobilin in Stretched Polyvinyl Alcohol Films

X-ray diffraction, polarization microscopy and polarized spectra of chlorophyllin and Congo red in polyvinyl alcohol (PVA) indicate that this is a two-phase medium which also affects the spectral properties of the chromophores. However, in most cases, conclusions are still permitted about transition moment directions from measurements of polarized absorption and emission spectra of dye in polyvinyl alcohol. With the aim of trying to estimate the shape of phycoerythrobilin and phycocyanobilin, the polarized components of absorption and emission spectra as well as fluorescence excitation spectra in polyvinyl alcohol film, stretched to various degrees, were measured. A dye of elongated shape (congo red) was used as an orientation standard. During the process of elongation the concentration ratio between the acidic and basic phycoerythrobilin forms was found to change. This effect is explained by the two-phase nature of polyvinyl alcohol and a change in volume ratio of these phases. The low anisotropy of the absorption and emission spectra of phycoerythrin and phycocyanin chromophores, as well as the ratio of their long to short wavelength absorptions, strongly suggest that they adopt at least partially coiled shapes in the polyvinyl alcohol solvent. The phycoerythrin and phycocyanin chromophoric groups probably have different tendencies to be coiled also in their pigment—protein complexes, as is corroborated by previous results for phycocyanin spectra in the same anisotropic medium.