The photoisomerization of two thioindigo dyes, 6,6'-dihexyloxythioindigo (1) and 6,6'-diethoxythioindigo (2), has been investigated in Langmuir-Blodgett films, supported multilayers, micelles, reversed micelles, and vesicles. Although each dye photoisomerizes in both directions in solutions, in the assemblies the photoisomerization is selectively cis -* trans. The cis -*• trans photoisomerization in films has been studied by several techniques and found to decrease in efficiency as the surface pressure on the film is increased. Photoisomerization efficiencies are generally low in the other assemblies as well. The results are attributed to the stability of a transoid triplet relative to a perpendicular triplet which can decay to both cis and trans.

Previous studies from our laboratories and elsewhere have shown that amides between fatty acids and the synthetic a,a,a,a-tetra (0-aminopheny1)-porphyrins exhibit good surfactant properties which facilitate their incorporation into structured assemblies characterized by hydrophobic-hydrophilic compartmentalization. This paper will focus on a number of aspects of our studies of these porphyrins at different interfaces.The a,a,a,a (4,O) isomers are readily incorporated into Langmuir-Blodgett films as either free base or metal complexes. Studies of assemblies containing free base and palladium (11) complexes have been carried out in which the porphyrin is irradiated in the presence of oxygen and nonexcited but oxidizable substrates. Much of the reactivity observed can be attributed to lo,* generation. These studies reveal the migration range and reactivity of activated oxygen in a structure related to biomembranes.Several of these synthetic porphyrins have also been examined in cell suspensions and in synthetic reversed micelle solutions. Studies in the former have shown that the porphyrins can mediate the photoinactivation of several enzymes located inside and within the mitochondria1 membrane in tumor cells extracted from rats. They are found to compare favorably to hematoporphyrin derivative in effectiveness.Studies of the same porphyrins in their reactivity towards copper ion incorporation in anionic reversed micelles indicate striking rate differences which can be interpreted in part to structural variations between the porphyrins as well as to their orientation at the hydrophobic-hydrophilic interface.

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