Synthesis, Structure And Properties Of Novel Conjugated Polymers With Thiazolo-fused Units

Conjugated organic polymers are widely used in many practical fields, especially in polymerssolar cells as photovoltaic materials, due to their designable features with many different categoriesand their superior characteristics, such as light weight, easy coating in solution, and flexiblefiguration. It is reported that the synthesis of low band gap organic conjugated polymers is the mostimportant methods to improve the power conversion efficiency (PCE). The literature investigationdisclosed that ultimate polymers used in organic solar cells are based on a donor-acceptor structure,with which donor parts are generally electron-rich thiophene or fused thiophene ring, while theacceptor part are generally low electron density of benzene ring or five-membered heterocyclicelectron withdrawing groups. Thiazole ring is a special kind of five-membered heterocyclic ring,and the thiazole ring is in a lower π-electron density than the thiophene ring, because a C atom inthiophene ring is replaced by a N atom of a greater electronegativity value. Therefore, in acopolymer of thiazole and thiophene, the thiazole can be used as a electronic part. Previous studyrevealed that the thiazole ring in the polymer backbone can play the role of the charge transfer, andcopolymers with fused thiophene ring units are a potential material with good electron transferproperties. This disertation will be engaged in the synthesis of prospective monomers andcopolymers, which two kinds of monomer containing thiazole ring and several monomers withthiophene ring were prepared, and two novel conjugated polymers were obtained. Physicalproperties and electrochemical performance of the synthesized polymers were also examined. Thisinvestigation may put a good foundation for the study of synthesis and properties of novelconjugated polymers with thiazolo-fused units in the future.The research is mainly concluded as follows:Several monomers of containing thiazole ring and containing thiophene ring were synthesized,including two monomers of benzothiophene, two monomers with thiazole ring, and fourmonomers with thiophene ring, which are named as4,7-dibromo-2,1,3-benzothiadiazole,4,7-Bis(phenyl)-2,1,3-benzothiadiazole,4,7-Bis(bromobenzeneyl)-2,1,3-benzothiadiazole;4,5-Bis(bromomethyl)thiazole,4,5-Bis(bromomethyl)-2-iodinethiazole,4-hexyl-2,5-dibromothiazole;2-bromo(methoxy-phenyl)thiophene,2,5-diphenylthiophene,2-bromo-5-phenylthiophene, and2-phenyl-5-bromophenylthiophene respectively. An organotin with thiophene ring,2,5- Bis(trimethylstannyl)thiophene, was also synthesized, which can be easily decomposed in thecolumn separation process.2,5-Bis(trimethylstannyl)thiophene can be purified with hexanerecrystallization. The above synthetic compounds were characterized by GC-Mass and1H NMRrespectively.The alternating copolymerization of the donor units and acceptor units were realized. Twodifferent dibromothiazole monomers were copolymerized with organotin, and two novel organiccopolymers PBeTh and PTzTh were synthesized. The structure of two copolymers was verified by1H NMR,13C NMR and GPC tests. It is proved that copolymers have good solubility inconventional solvents, such as dichloromethane, chloroform, and tetrahydrofuran, which indicatesthat they should show better performance in coating process. The polymer of moderate molecularweight was separated from larger ones by using a methanol recrystallization. An resolution toseparate the polymer with moderate molecular weight in polymerization have been obtained.Molecular weights of the polymer were tested by gel permeation chromatography (GPC).Optical properties and electrochemical properties of the synthesized polymers were tested by UVand CV. The results showed that the maximum absorption wavelength of polymer PTzTh andPBeTh in Chloroform solution were469nm and334nm, respectively. The maximum absorptionpeak of PBeTh shows a135nm shift to blue compared with that of polymer. EA(LUMO level) ofPBeTh is higher than PCBM (C60) by0.3eV, which EAof the polymer PBeTh is-3.91eV and EAof PCBM (C60) is-4.2eV. And the Eg of PBeTh is1.72eV, which can absorb great amount of thesun light and match the solar spectrum well. So PBeTh may have potential application as anelectron acceptor material in organic solar cells.