| An approach to investigate the possibility that rigid rod polymers can conduct has been made. Thus efforts to understand the electronic behavior of these high performance polymers were directed toward calculating the band gaps, band widths, ionization potential and crystal packing of these polymers so as to predict their potential and applicability as conducting materials which could replace the conventional inorganic semiconductors.; The preferred conformation was obtained in each polymer using the EHMO method. In the most stable (minimum energy) conformations of AAPBO, ABPBO, AAPBT, ABPBT, and PDIAB polymers, the axial band gaps were found to be 1.86, 2.31, 1.94, 2.08 and 1.55 eV, respectively. All of these values are in good agreement with the results of theoretically investigated model compounds of PBTs and PBOs, and also experimental estimates 1.4 to 1.8 eV of polyacetylene, a prototye polymer much studied because of its unique electronic properties. In order to analyze the charge-transfer taking place in a polymer-dopant matrix, an initial attempt was made to investigate the band structure and partial oxidation of a bis(oxalato)platinate complex through EHMO methods. A partial oxidation x = 0.35e for platinum at an optimum separation of r(,Pt-Pt) = 2.845 (ANGSTROM) was obtained with a stair-case arrangement between the consecutive oxalate ligands. The effect of doping on band gaps of PDIAB polymer was studied by doping the host polymer with I(,3)('-) and Br(,3)('-) anions. A very small band gap of the order of 0.1 eV was obtained due to the strong polymer-dopant interactions and the electron delocalizations, as compared to the undoped PDIAB polymer. The results also indicate that the bromine- doped PDIAB has larger band gap than the iodine- doped polymers. The technological potential of these polymers is particularly noteworthy because doped films of these polymers have extremely wide range of conductivities. In some final calculations, the recently developed ab-initio quality VEH technique was used to study the electronic band structure of PDIAB polymers. The band gap (2.93 eV) and the ionization potential (5.4 eV) obtained for the PDIAB chain in the coplanar conformation was compared with the corresponding values of the similar -NH containing polymers and also with the results obtained from employing the EHMO method. (Abstract shortened with permission of author.)... |
