Synthesis of low band gap polymers

Cammisa, Eduardo G. (2000) Synthesis of low band gap polymers. Masters thesis, Memorial University of Newfoundland.

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Abstract

A novel synthetic pathway to 4H-cyclopenta[2,l-b:3',4’-b’] dithiophen-4-one 2-8, which is a valuable precursor for a variety of low band gap polymers, has been developed. From 2-8, the derivatives 4,4’-bi-(4H cyclopenta[2,l-b:3',4’-b’] dithiophenylidene) 2-34 and 2,6-dibromo-4H cyclopenta[2,l-b:3',4’-b’] dithiophen-4-one 2-36, were prepared. A poly(4H-cyclopenta[2,l- b:3’, 4'-b’]dithiophen-4-one) (poly 2-8) film was modified by chemical reaction with Lawesson's reagent giving a new material, which exhibited a smaller band gap (0.8-1.0 eV) than the starting poly 2-8 (1.1-1.2 eV). Compound 2-34 was electrochemically polymerized and cyclic voltammetry showed that the resulting polymer has a low band gap (0.5-0.9 eV), consistent with a theoretical prediction. Compound 2-36 is a useful starting material for the synthesis of new polymers. -- The known compound 2,2'-(ethyne-l,2-diyl)bis(thiophene) 3-3 was synthesized using an adaption of a literature procedure, and 3-3 was used for the synthesis of its novel derivatives 4,5-di-thiophen-2-yl-1,3-dithiol-2-one 3-5 and tetrathien-2-yl-thiophene 3-6. Electrochemical polymerization of 3-6 gave a polymer with a band gap of ca. 1.8 eV. -- Dithieno[3,2-c:2',3’-e][1,2] dithiin 4-1 was prepared by using a literature method. Electrochemically prepared films of poly 4-1 did not show any electroactivity for the disulfide bridge in acetonitrile.

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