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Title:Porphyrin liquid crystals
Author(s):Patel, Bimal Ramesh
Doctoral Committee Chair(s):Kenneth S. Suslick
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Chemistry, Organic
Engineering, Materials Science
Abstract:A new family of tetraarylporphyrins has been synthesized. The key distinguishing feature of these porphyrins is the presence of carboxylic functionality at the eight meta-phenyl positions of tetraphenylporphyrin (TPP). The base porphyrin is called 5,10,15,20-tetrakis(3$\sp\prime,5\sp\prime$-dicarboxyphenyl)porphyrin (H$\sb2$DCarPP). The octa-meta-phenyl substitution pattern allows substituents at the meta positions to direct out and away from the molecular center in three dimensions. These outward-directed alkyl groups created pockets above and below the porphine plane. The "bis-pocket" shape is the critical design feature that gives this family of porphyrins novel and exciting properties.
The synthesis and characterization of H$\sb2$DCarPP, starting with mesitylene, is presented in Chapter 2. A benchtop process for oxidizing mesitylene to uvitic acid has been developed, and it is the key step to obtaining H$\sb2$DCarPP on a gram scale. An unusual crystal structure of an octapyridine-H$\sb2$DCarPP complex is also presented. This host-guest structure shows large, solvent-filled channels in one dimension, and porphyrin-pyridine-porphyrin layers in the other dimensions.
Octa-n-alkyl esters of H$\sb2$DCarPP have also been prepared. The synthesis and characterization of these alkyl H$\sb2$DCarPP derivatives are presented in Chapters 3 and 4. The C$\sb{10}$ to C$\sb{22}$ octa-n-alkyl esters are liquid crystals. In fact, the C$\sb{10}$ and C$\sb{12}$ derivatives are liquid crystalline at room temperature. The C$\sb{10}$ derivative has a liquid crystalline temperature range from $-3\sp\circ$C to 120$\sp\circ$C, the largest range of the series. The bis-pocket shape of the $\rm C\sb{12}\ H\sb2$DCarPP allows it to retain its liquid crystalline properties when metalated with five-coordinate metal ions like the vanadyl ion (VO$\sp{\rm II}$). By comparison, $\rm C\sb{12}\ H\sb2$TCPP (5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin), a relatively flat molecule, loses its liquid crystalline properties when it is metalated with the vanadyl ion.
The alkyl H$\sb2$DCarPP liquid crystals were studied by polarized microscopy. A model for the structure of the liquid crystalline phase is developed from analysis of the birefringence textures of the homologous series of alkyl H$\sb2$DCarPP liquid crystals. X-ray diffraction studies contribute additional information about the mesophase structure. The electron paramagnetic resonance of the C$\sb{12}$ DCarPPVO complex at room temperature gives a broad isotropic signal with lack of hyperfine structure.
Issue Date:1996
Rights Information:Copyright 1996 Patel, Bimal Ramesh
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712399
OCLC Identifier:(UMI)AAI9712399

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