Synthesis And Characterization Of Conjugated Polymers With Push-pull Electronic Structure

Conjugated polymers with a push-pull electronic structure have unique photoelectrochemical properties and are applied in solar cell materials. Design and synthesis of polymers with excellent properties is the key to improve the photoelectric conversion efficiency of organic solar cells. In this paper, we synthesized a series of new polythiophene derivatives with good thermal stability and solubility. Bying researching the photoelectric properties of the polymers, we study the relationship between the molecular structure and their properties. The main contents are as follows:(1) We synthesized a series of monomers such as 4, 7-di(4–hexyl–thiophen-2-yl)-2, 1, 3-benzothiadiazole(M1), 1, 3-Bis-(4-hexyl-thiophen-2-yl)-5-octyl-thieno[3,4-c]pyrrole-4, 6-dione(M4),5-Octyl-1,3-di-thiophen-2-yl-thieno[3,4-c]pyrrole-4, 6-dione(M6) and 5-(2-ethyl-hexyl)-1,3-di-thiophen-2-yl-thieno[3,4-c]pyrrole-4, 6-dione(M7).And by anhydrous ferric chloride method,polymers P1-P3 were polymerized. The results show that the photoelectric properties of polymer P1 which have more alkyl chain in the backbone decrease because of bigger steric hindrance and bigger torsion angle.(2)By Suzuki coupling reaction,We obtained P4 with 2, 7-dibromo–9–hexyl-carbazole(M11) and 4, 7- two(acid pinacol ester)-2, 1, 3- benzothiadiazole as raw materials and we synthesized P5 with 2, 7-Dibromo-9-(2-ethyl-hexyl)-9H-carbazole(M12) and 4, 7- two(acid pinacol ester)-2, 1, 3- benzothiadiazole as raw materials.The results show that, different alkyl chains to the same position have less influence on the photoelectric properties of polymers.(3) We obtained polymers P6-P8 by Still coupling reaction using 2,5-dibromo-7,7-di(2-ethylhexyl)-7H-3,4- dithia-7- sila- cyclopent [a] pentalene respectively with 1,3-dibromo-5-octyl- thieno [3,4-c] pyrrole-4,6-dione, 4, 7-Bis-(5-bromo-thiophen-2-yl)-be nzo(2,1,3)thiadiazole(M3) and 1,3-bis(5-bromo- thiophen-2-yl)-5-octyl- thieno [3,4-c] pyrrole-4, 6- dione(M8). The results show that, the polymers P6-P8 have wide li ght absorption wavelength and narrow band gap due to the introduction of bithiophene silole.All of the monomers above were confirmed by IR, 1H-NMR, 13 C-NMR, and melting point detection.For polymers,optical properties were studied by ultraviolet-Visible(UV) absorption spectrum and fluorescence spectrum(FL), thermal performance is studied by differential thermal curve(DSC) and thermogravimetric curve(TGA), molecular weight was measured by liquid gel chromatograph and electrochemical properties were studied by Testing cycle volt-ampere curve. Finally, by calculating all these data, we obtained the optical band gap, degree of polymerization, decomposition temperature, electrochemical band gap and HOMO / LUMO orbital energy of the polymers.