ARRANGEMENT OF A HYDROPHOBICALLY SHIELDED PORPHYRIN, ,15,20-TETRAKIS(3,5-DI-TERT-BUTYLPHENYL)PORPHYRIN, IN OCTADECYLAMINE LANGMUIR-BLODGETTMULTILAYERS

A hydrophobically shielded porphyrin, 0,15,20-tetrakis(3,5-di-tert-but ylphenyl)porphyrin (TBP), and 5,10,15,20-tetra(p-tolyl)porphyrin (TTP) were comparatively studied in octadecylamine (ODA)-based monolayers a nd Langmuir-Blodgett mono- and multilayer films. Regardless of its con centration, TTP was found to undergo severe aggregation resulting in a pproximately a 100- fold decrease of the fluorescence lifetime relativ e to homogeneous solutions. In contrast, TBP exhibited far less tenden cy to aggregate. In the case of diluted films, where the TBP/ODA ratio was 1:99 or lower, two-component emission decay curves were observed with the lifetimes of 9 and 4 ns, which can be attributed to the coexi stence of monomeric and dimeric forms of the porphyrin. An increase in TBP concentration led to a gradual decrease of the lifetimes; however , they remained longer than 1.5 ns even at a TBP/ODA ratio as high as 1:3. With TBP/ODA ratios less than 1:4, the isotherms exhibited a phas e transition at approximately 20 mN/m. As may be suggested from the mo lecular areas, TBP molecules can generally be adopted in two forms whe n embedded in an ODA matrix. One form presumes monomeric molecules ori ented perpendicular to the film plane, and the other form comprises fa ce-to-face dimers with porphyrin macrocycles aligned parallel to the f ilm plane.