The Study On The Geometries, Electronic Properties And Conductivity Of Furo [3,4-b] Pyridine-type Heterocyclic Compounds

In this paper, we used density functional theory (DFT) to study the geometries and electronic properties of Furo[3,4-b]pyridine-type heterocyclic compounds, from monomer, oligomer to polymer. The relationship of the geometries, electronic properties of monomer, oligomers and polymer are elaborated, and the influences of nitrogen atoms substitution on the band gaps of the polymers are also discussed. We also calculated the structures, electronic properties and electrical conductivity of the copolymer that thiophene, furan, pyrrole are used as electron donor, and furan [3,4-b] pyridine-type heterocyclic units are used as a acceptor.In chapter 1, we briefly introduce the status of organic conductive polymers, practical values, conductive mechanism, design principles and so on. Because they have great potential for the development of electronic devices and other fields, conjugated oligomers and polymers have been extensively investigated for both academic and industrial applications. At the end, the purpose of our work is briefly stated.In chapter 2, we elaborated the concept of the DFT method utilized during our computing and the programs implementing the method. Moreover, several analysis methods employed in this paper are also introduced, including AIM, NBO, and NICS.In chapter 3, the electronic structures of six different furo[3,4-b]pyridine-type heterocyclic compounds (they are FPD, FPZ, FPDZ, FPMD, FTZ1, and FTZ2) are studied, from monomer, oligomer to polymer. For these compounds, we analyzed and discussed the influence of the nitrogen atoms substitution's number on their structure, electronic properties, and the conductivity. And their internal relations between the electronic structure and energy gap of oligomers and polymers are discussed by means of the atom in molecule(AIM), the natural bond orbital(NBO), and nucleus- independent chemical shift(NICS). In this study, we discussed in detail the properties of central bond in oligomers and polymers. The change of NICS as a method examining conjugational degree is reported. The change of NICS shows that the conjugation in central section are stronger than that in outer section, and the structure in central are closer to quinoid structure. We also calculated the polymers'period boundary condition, and obtain the band structure. The band structure analysis show that these polymers all have narrow energy gap, they can be consider as intrinsic conductor.In Chapter 4, the thiophene and thieno[3,2-b]thiophene are used as electron donors, FPD, FPZ, and FTZ are used as electron acceptors, so we got six co-polymers(they are FPD-th, FPZ-th, FTZ-th, FPD-tt, FPZ-tt, and FTZ-tt). We intend to understand the difference of conductivity by their electronic structures studies. The change of NICS shows that the conjugation in central section are stronger than that in outer section. The band structure analysis show that these polymers all have narrow energy gap, especially for thiophene based polymers. They are potential conductive material.In chapter 5, we used furan and pyrrole as electron donors, and FPD, FPZ, and FTZ are used as electron acceptors, so six alternating donor and acceptor conjugated copolymers are obtained. We study their structures and electronic properties by means of the atom in molecule(AIM), the natural bond orbital(NBO), and nucleus-independent chemical shift(NICS). The changes of NICS also show that the conjugation is stronger in the central section than in the outer section. The H-bonding interaction and N-substitution in the acceptors play a very important role on the geometries, electronic structures and the energy gap. The theoretical results suggest that pyrrole-based polymers are good candidates for conducting materials, compared with furan-based polymers. With the increase of nitrogen atom substitution in the acceptors in these polymers, the intermolecular charge transfers along the polymeric axe are enhanced, and the bond length alternations, the HOMO-LUMO energy gap (Eg) for these polymers are decreased. The results suggest that the six polymers all have lower energy gaps (in the range of 0.81-1.26 eV), which indicate that these proposed polymers are good candidates for the n-doping conductive materials, especially for (FTZF)n and (FTZP)n.