D. Wrobel et al., CHLOROPHYLLS IN POLYMERS .2. PHEOPHYTIN A IN POLYMERS AND THE INFLUENCE OF STRETCHING ON THE STATE OF CHLOROPHYLLS IN ANHYDROUS POLYMER-FILMS, Photochemistry and photobiology, 62(2), 1995, pp. 290-298
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.