Synthesis And Study Of Fluorinated Thiophenes, Bithiophenes And Trithiophenes: Models For The Polymeric Material

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Synthesis And Study Of Fluorinated Thiophenes, Bithiophenes And Trithiophenes: Models For The Polymeric Material

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Title: Synthesis And Study Of Fluorinated Thiophenes, Bithiophenes And Trithiophenes: Models For The Polymeric Material
Author: Turkman, Nashaat
Abstract: 3-Fluorothiophene is a small molecule and the known syntheses for this molecule are far from being straight forward and suffer from many drawbacks such as low yield, long synthetic procedures and the use of expensive or dangerous fluorinating agents. The synthesis of 3-fluorothiophene was accomplished in four steps and 49% overall yield by a very convenient method. 2,5-Dibromo-3-fluorothiophene was prepared in essentially one step synthesis involving a decarboxylation-bromination reaction. Both 3-fluorothiophene and 2,5-dibromo-3-fluorothiophene are potential monomers for a wide variety of fluorinated polythiophenes. Fluoroalkyl thiophene monomers, dimers and trimers were prepared. 3-Heptanoylthiophene is a key intermediate in the synthesis of the fluorinated monomers, dimers and polymers. The synthesis of 3-heptanoylthiophene by the reversible umpolung methodology was accomplished. This methodology has several advantages over the Grignard method such as: no undesirable byproducts were formed, cleaner and straightforward reactions, easier purification process and improved overall yield. The synthesis of 3-(1,1-difluoroheptyl)thiophene and 2,5-dibromo-3-(1,1-difluoroheptyl)thiophene were accomplished. These are interesting monomers which are upon polymerization they could lead to novel conducting polymers. The monomer contains alkyl side chain that renders the corresponding polymer soluble in organic solvents, which is necessary for the processing of the polymer. The fluorinated polymer is anticipated to have remarkable features such as high thermal and oxidative stability, a relatively higher hydrophobicity and lipophobisity in combination with the electrical conductivity. The synthesis of the head-to-tail 3,4'-bis(1,1-difluoroalkyl)-2,2'-bithiophene: model for the corresponding fluorinated polythiophene was accomplished. Unfortunately, this dimer was a liquid and we were not able to obtain its crystal structure. This was motivating for the preparation of the novel molecule: head-to-tail 3,4',4''-tri(difluoromethyl)-2,2':5',2''-terthiophene which was crystallized and studied. This trimer has revealed an interesting inter- and intramolecular fluorine-sulfur interactions that shaped the molecule in the solid state. The sulfur-fluorine intramolecular distance is significantly shorter than the sum of the van der Waals radii. Based on the structural features and the face-to-face packing style, this molecule is an excellent model for an n-type oligomer or polymer. The two-dimensional face-to-face π-stacking motif is very advantageous to high charge mobility which makes the corresponding oligomer an ideal candidate for OFET (Organic Field Effect Transistors) devices.A significant progress was made toward the synthesis of fluorinated fused five-membered ring systems. 1,3-dichloro-5,6-dihydrocyclopenta[c]thiophen-4-one is a key monomer was prepared using the literature method. The synthesis of 1,3-dichloro-4,4-difluoro-5,6-dihydrocyclopenta[c]thiophene which is a fluorinated thiophene monomer was accomplished. The synthesis of the H-T 3,3'-dichloro-4,4',5,5'-tetrahydro-1,1'-bi(cyclopenta[c]thiophene)-4,6'-dione and H-H 3,3'-dichloro-4,4',5,5'-tetrahydro-1,1'-bi(cyclopenta[c]thiophene)-6,6'-dione dimers were accomplished, although the isolation and purification of those dimers were not complete the crystals of both dimers were obtained. Unfortunately we were not able to resolve the x-ray crystal structures.
Date: 2009-09-16
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