CHLOROPHYLLS IN POLYMERS .2. PHEOPHYTIN A IN POLYMERS AND THE INFLUENCE OF STRETCHING ON THE STATE OF CHLOROPHYLLS IN ANHYDROUS POLYMER-FILMS

In the first part of this study the spectral properties of pheophytin a in rigid, unstretched anhydrous polyvinyl alcohol and nitrocellulose films have been studied in order to establish the influence of the ce ntral magnesium atom on the stare of chlorophylls in polymer systems. The absorption, fluorescence, excitation spectra and fluorescence inte nsity decays in the polymer films and in the solutions from which they are cast are reported. It is shown that pheophytin a aggregate format ion is influenced by the nature of the polymer system. An aggregate of pheophytin a is found in polyvinyl alcohol films over a wide concentr ation range. On the other hand, pheophytin a exists in the monomeric f orm in unstretched nitrocellulose films at concentrations below 6 X 10 (-6) mol/g. In the second part of this work, the influence of stretchi ng of the films on the state and distribution of embedded chlorophyll pigments, is described. Here we show that the chlorophyll a molecules are found to undertake a heterogenous distribution in polyvinylalcohol matrices, since stretching partially disrupts the pocket-like structu res present in unstretched films. In contrast, chlorophyll a and pheop hytin a molecules can be embedded in a monomeric state in nitrocellulo se matrices and moreover they remain homogeneously distributed upon st retching. The chlorophyll/nitrocellulose system is concluded to be a u seful model system for studies of donor-donor energy transfer processe s.