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https://hdl.handle.net/2142/21096
Description
Title
Porphyrin liquid crystals
Author(s)
Patel, Bimal Ramesh
Issue Date
1996
Doctoral Committee Chair(s)
Kenneth S. Suslick
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Chemistry, Organic
Engineering, Materials Science
Language
eng
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.
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