The Electronic Properties Of Conjugated Polymers And Their Monomers And Oligomers

Several conjugated polymers with all atoms on the same plane are studied,based on density functional theory(DFT)methods,in this paper.The electronic properties of monomers and oligomers of the polymers are also computed and analyzed.The relationship of the electronic properties of monomer,oligomers and polymer are elaborated and the influences of different substituent groups on the band gaps of the polymers are also explicated.In chapter 1,the information of conducting polymers is briefly introduced and the conjugated polymers with the special structure,which are studied widely in the searching of good conducting polymers,are the focus.And at the end,the purpose of our work is briefly stated.In chapter 2,the concept of the DFT method utilized during our computing and the programs implementing the method are elaborated.Moreover,several analysis methods employed in this paper are also introduced,including NICS,NBO,and AIM.In chapter 3,The electronic structures of monomers,oligomers and polymers of poly(p-phenylenevinylene)(PPV)and their derivatives including PO,PFA,PFB,PCN, POCN are calculated and analyzed.The influences of the substituent groups on the band gaps of the polymers are elaborated and the structure aspects such as the bond length alternative are also involved.Also,the influences of the substituent groups on the electronic properties such as energy gaps of the monomers and oligomers are analyzed too,and the emphasis is the NICS.Additionally,the relationship of the electronic properties of the oligomers and polymers are illustrated through the NBO and NICS analysis.The analysis of the Wiberg bond index of the oligomers reveals that the WBI of oligomer are similar while their polymers have a close band gap. Moreover,the result of the analysis of the NICS of the oligomers is the same,showing that the NICS values of the oligomers of the polymers with close band gaps are similar too.In chapter 4,poly(thieno[3,4-b]pyrazine),poly(6H-pyrrolo[3,4-b]pyrazine), poly(furo[3,4-b]pyrazine),and their oligomers are studied.The method using NICS values as a measure of the conjugated degree is introduced.The analysis of NICS values reveals that the conjugated degree of the bonds at the center are stronger than those at the sides and the conjugated degrees of the rings closer to the chain change much more.In chapter 5,several poly(thieno[3,4-b]pyrazine)derivates and their oligomers are studied based on the DFT method.The analysis of the band structure show that there is no strong relationship between the energy gaps of oligomers and band gaps of polymers,that is when the energy gaps of oligomers of a polymer are larger than another the band gap of the polymer may be smaller than the other.