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Design, synthesis and mesomorphic behavior of 2,5-disubstituted pyridine liquid crystals

Getmanenko, Yulia A
http://rave.ohiolink.edu/etdc/view?acc_num=kent1185592311

Abstract Details

2007, PHD, Kent State University, College of Arts and Sciences / Department of Chemistry.
Calamitic (rod-like) 2,5-disubstituted pyridine liquid crystals were synthesized, their mesomorphic properties were examined by DSC analysis and polarized optical microscopy, and the charge transport properties of the selected materials were studied by the time-of-flight technique. The Negishi coupling of 2,5-dibromopyridine with alkyl- and arylzinc chlorides resulting in 2-substituted-5-bromopyridine was used as a key step in the construction of the variety of mesogens. Isomeric 2-bromo-5-substituted-pyridines can be prepared by Negishi or Stille coupling of 2-bromo-5-iodopyridine, and in this case the reaction takes place at the C-I site with good selectivity. The literature reaction conditions used for the preparation of 2-substituted-5-methylpyridines were optimized for 3-alkylpyridines with longer tails, and 2-iodo-5-alkylpyridines and 2-tri-n-butylstannyl-5-alkylpyridines were prepared and used as important intermediates for the construction of phenylpyridine, phenyl-bipyridinyl and thiophene-pyridine liquid crystals. A new convenient approach to 2-substituted-5(or 6)-tri-n-butylstannylpyridines was developed using the mild conditions of Negishi coupling of 2-bromo-5(or 6)-tri-n-butylstannylpyridine with organozinc chlorides. Literature conditions (i-PrMgCl, THF, room temperature) used for the synthesis of several 2-bromo-5(or 6)-substituted-pyridines were extended to the preparation of 2-bromo-5(or 6)-tri-n-butylstannylpyridines, and this method is a good alternative to a standard approach which utilized n-BuLi/ -78 °C conditions. The change of the solvent from THF to toluene led to the isomeric 2-tri-n-butylstannyl-5-bromopyridine isolated in good yield. New 2-substituted-5-tri-n-butylstannylpyridines are stable and can be purified by Kugelrohr distillation in most cases or by column chromatography on untreated silica gel. These pyridinylstannanes were exstensively used for the preparation of mesogens constituted of different combinations of 2,5-disubstituted pyridine and thiophene rings. Tetrasubstituted imidazoles were synthesized and their glass forming properties were studied by DSC analysis. Intoduction of N-3-Phenyl-propyl substituent in parent N-H-imidazoles resulted in a substantial reduction of the melting point and formation of stable organic glasses with Tg above room temperature. A series of liquid crystals with dithieno[3,2-b;2’,3’-d]-thiophene core were prepared as potential semiconductors by the Stille coupling with thienylstannanes.
Robert Twieg (Advisor)
447 p.
Chemistry, Organic
phenylpyridine LCs; thiophene-pyridine LCs; pyridinyl stannanes; selective Negishi coupling; liquid crystal semiconductors; smectic liquid crystals

Recommended Citations

Citations

  • Getmanenko, Y. A. (2007). Design, synthesis and mesomorphic behavior of 2,5-disubstituted pyridine liquid crystals [Doctoral dissertation, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1185592311

    APA Style (7th edition)

  • Getmanenko, Yulia. Design, synthesis and mesomorphic behavior of 2,5-disubstituted pyridine liquid crystals. 2007. Kent State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1185592311.

    MLA Style (8th edition)

  • Getmanenko, Yulia. "Design, synthesis and mesomorphic behavior of 2,5-disubstituted pyridine liquid crystals." Doctoral dissertation, Kent State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=kent1185592311

    Chicago Manual of Style (17th edition)

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© 2007, all rights reserved.
This open access ETD is published by Kent State University and OhioLINK.