Excited Polaron In The Pernigraniline-base Polymer

Abstract: Polyanilines have attracted a great deal of attention in the past decade as a new class of organic conducting materials. The conduction mechanism of them is different from metals or inorganic semiconductors. Carriers in them are made up of solitons, polarons and bipolarons what are nonlinear excitations in the polymer. Experimental observations have been showed that the conductivity is increasing with applied pressure. In present theoretical work,Gao Yuan-Liang tried to study Structure varies of the polymer and its conduction mechanisms under pressure. The results showed that the band gap of the polymer were reduced with increasing pressure. This article is aware that because of bandgap narrowing, the two states in the bandgap low less likely to arouse the electron to the higher high, the formation of excited polaron.For excited polaron, new carriers which may exist in polyaniline under pressure, we need to do some research in theory, in order to provide a theoretical basis for experimental workThe present work studied the pernigraniline-base (PNB), an oxidized form of polyaniline. On the basis of the extended Ginder-Epstein (GE) model,we describe firstly geometric structure and electronic structure of PNB under the different chain length; Secondly, on polaron (a hole polaron as an example)the PNB polymer high-excited state may exist,we carry out self-consistent variational calculation, give the system geometry, electronic structure and optical absorption spectra; Thus, molecular dynamics simulation was used to study stabilizing process of excited polaron in the polymer.Firstly,we investigated self-consistent-variation ground states of a pernigranine-base polymer with various values of the chain length in the extended Ginder-Epstein model, The results showed that the geometry structure and electronic structure of the polymer were related to characteristic 0f monomer number, besides chain length N. 4n+2 and 4n systems possessed different electronic states; When N<40, torsion angles of benzenoid rings and band gap were increased with decreasing N, while that of quinoid rings and bond order wave were decreased with the decreasing N; When N >>40,those diversities all disappeared, and the structure of the polymer was tend to stabilization.Secondly,excited polaron in the pernigraniline-base polymer was investigated in an extended Ginder-Epstein model. In comparison with a common polaron, the excited showed some different nature: its lattice relaxasion was wider and deeper; the two gap levels got nearer. In our calculated absorbance for the excited polaron there was only one peak of low energy(~1.2eV) and its intensity got a rise of ~60%. In the case of the higher electron-libron coupling, energy of excitation for an excited polaron was 12.65eV, which was 1.27eV higher than that of the common. The facts offered a criterion to distinguish an excited polaron from a common one.Thus, molecular dynamics simulation was used to study stabilizing process of excited polaron in the polymer, the system reproduced the evolution of the BOW ,the ring-torsion angles and optical absorption spectra in the 0-500 fs. The results showed, after around 300 fs, excitation level of the electronic structure is stable, the geometry structure,such as the BOW ,the ring-torsion angles, is totally stable, and, the absorption peak at 1.2eV has been completely stable, excited polaron is completely generated, the system stability.