Reducing Of Ring-torsion Angles And Band Gap Of An Emeraldine-base Polymer Under High Pressure

Polyanilines have attracted a great deal of attention because of its variety structure,nice stability,particular adulteration mechanism and widely application foreground. The conduction mechanism of them is different from metals and inorganic semiconductors. Carriers in them are made up of solitons, polarons and bipolarons what are nonlinear excitations in the polymer. Besides, many experimental observations have been showed that the conductivity of polyaniline is increasing with applied pressure until a saturate value 3.2―10GPa. We think the difference is due to the different oxidation degree. In present theoretical work, there is one and only about pernigraniline-base (PNB) which the saturate value is about 7.6 Gpa. As for lower saturate value(3-4Gpa) what happened, there is no explain at present. So we study emeraldine-base (EB) polymer in this article and try to know the applied pressure how to change the geometric structure and electronic structure of EB polymer.We investigated self-consistent-variation ground states of the EB polymer with various values of structure parameter V4,0 from 1.8 to 35.8eV in the framework of the extended Ginder-Epstein model. Variation ground states of the polymer were investigated with various values of structure parameter V4,0 in the extended GE model. Changing V4,0 , while keeping other parameter fixed, we found that ring-torsion angles were sensitive to V4,0. Therefore, we estimated pressure on a ring by changes of its torsion angle. Relations between estimated pressure and V4,0 , the ring-torsion angles, and the band gap were built. The results showed that the theoretical pressure augmented with increasing V4,0 meanwhile the ring-torsion angles and the band gap was reduced. When the pressure increased to 3.0GPa, the gap reduced from 2.01eV to a minimum 0.87eV. This theory is consistent with the experimental observation for the conductivity of the polymer under high pressure. So the pressure vertical to the chain made the ring-torsion angles and the band gap was reduced. That's why the conductivity of the polymer increased.Furthermore, Calculated absorption spectra of the polymer under pressure were given out: while increasing pressure up to 3.0 GPa, theπ—π* absorbance took a blue-shift from 2.01eV to 0.87eV. The spectra provide a way to calibrate pressure.