OPTICAL PROPERTIES OF PROTOCHLOROPHYLL PIGMENTS .2. ELECTRONIC ABSORPTION FLUORESCENCE AND CIRCULAR DISHROISM SPECTRA

An analysis is presented of the electronic absorption spectroscopic properties of the protochlorophyll pigments by means of the fluorescence excitation and emission spectra, fluorescence polarization, and circular dichroism. From the fluorescence emission and polarization spectra, assignments of the visible absorption bands to four electronic transitions and their vibrational components are made, and their relative orientations are deduced. The main red and blue bands of the protochlorophyll pigments show parallel polarization to each other, in contrast with the case of the chlorophylls where they are perpendicular. On the other hand, the first vibrational overtone of the red band presents a mixed x-y polarization. The circular-dichroism spectra correlate with the fluorescence polarization data, the red and blue regions each showing two circular-dichroism bands of opposite signs. The results are discussed in connection with the theoretical data available for the porphyrin pigments. © 1969.