In Chapter 1, the history of conducting polymers, especially polythiophene and its derivatives, was briefly reviewed. Different approaches of structural modifications to afford small bandgap polythiophene derivatives were discussed. The emergence of metal-containing polymers (metallopolymers) as functional materials has attracted tremendous attention around the world. Introduction of metals into thiophene-based oligomers and polymers, whether the backbone or the side chain of the π-conjugated framework, the electronic, optical, or magnetic properties of the material are expected to be significantly affected by metals through various mechanisms. Synthesis methods to prepare poly(thienylene vinylene) were also briefly reviewed in this chapter.
In Chapter 2, the motivations and objectives were briefly discussed. Two structurally similar compounds, thieno[3,4-d]-1,3-dithiole-2-thione and thieno[3,4-d]-1,3-dithiol-2-one are the starting point of this project due to their unique carbondithiolate structures, which may lead to metal-dithiolate coordinated oligomers or/and polymers, or polymers crosslinked by DTTTF units. For the preparation of monomers, six types of reactions were systematically studied with focus on thieno[3,4-d]-1,3-dithiol-2-one to prepare different direvatives. Different halogenated compounds, Mannich bases, chloromethylated compounds, a number of nucleophilic substituted derivatives and a DTTTF analogue from chloromethylated compounds were successful synthesized. All products were fully characterized through 1H and 13C-NMR, FT-IR, ESI-TOF high resolution mass spectroscopy. The halogenated products were prepared through halogensuccinimides or other halogenation reagents such as Br2, I2. These halogenated compounds may be candidates to prepare homopolymer and/or copolymers bearing carbondithiolate structures by cross-coupling reactions. 4,6-Bis(chloromethyl) thieno[3,4- d]-1,3-dithiol-2-one and its nucleophilic derivatives may be good monomers for the two-step precursor polymerization to achieve fully conjugated poly(thienylene vinylene) derivatives and even metallopolymers with metal-dithiolate coordinations.
Attempted polymerization reactions to homopolymers and copolymers through directly C-C coupling, such as transitional metal catalyzed cross-coupling, Stille reaction, and Ullman reaction, et al. were discussed in the beginning of Chapter 3. Base-promoted and acid-promoted polymerizations were attempted to afford soluble precursor polymers with carbondithiolate structures. However, all the symmetrical thiophene derivatives did not successfully yield processable precursor polymers; asymmetrical monomers generated some possibilities for future study. Synthesis of thiophene-based oligomers, such as dimmers (dithienyl compounds), trimers (trithienyl compounds), and heptamers were also explored in chapter 3, followed by preparation of thiophene-based copolymers through Wittig-Horner reactions. Properties of oligomers, especially trimers were well characterized by NMR, FT-IR, and ESI-TOF. Several conjugated DTTTF derivatives from trimers were prepared by the triethyl phosphite cross-coupling method. These conjugated DTTTF compounds posses some unique properties. They are stable in solid forms, but may be doped in solution forms. The copolymers were characterized by elemental analysis, and FT-IR. UV-Vis spectra of copolymers show their bandgap values are aroud 1.87eV (UV edge calculation).
In the Experimental chapter, all reaction conditions of preparation of new annulated thiophene derivatives and oligomers were documented in details. Physical and spectroscopic properties of these new compounds were also presented in this chapter.
Key words. polythiophene, oligomer, conjugation, synthesis, characterization, DTTTF, metallopolymer