Theoretical Study Of Polyaniline Doping Mechanism And Hydrogen Bond

Polyaniline as one of the typical conducting polymer has played an important role in conductivity, microwave absorpting and many other fields due to its diverse structures, high electrical conductivity, excellent physical properties and environmental stability. The most striking feature of polyaniline among conducting polymers is that the conductivity will significantly increased through doping, furthermore, the absorbing property will be enhanced accordingly. There have been many experiment researches based on the proton acid doping, however the theoretical studies about the doping process are not common.In this paper, we carried out the first-principles study on the mechanism of hydrochloric acid doped polyaniline. The study was focused on the equilibrium geometries of emeraldine base (EB) and emeraldine salts (ES), the natural bond orbital charge distribution, frontier molecular orbits and energy of singlet as well as triplet state. The calculated result showed that during the doping progress, the benzene and quinone rings turned into the intermediate structure and promoted the bipolaron delocalization, meanwhile, the rings tended to be coplanar and the conjugation was enhanced, hence, the conductivity as well as the absorptivity were elevated. During the transformation from bipolaron to polaron, the charge in quinone ring transfer to benzene rings, and the charge distribution of ES3was balanced indicating that doping progress promoted the charge mobility in the chain. The electrons transferred to the quinone ring and the ended benzene ring from HOMO to LUMO. The singlet energy of each configuration was under their corresponding triplet energy, and the ES1possessed the lowest singlet energy which to be the most stable structure.We also investigated the camphorsulfonic acid doped polyaniline progress, and there was the N-H...O=S type intermolecular hydrogen bond interaction in the solution system. From the geometric structure of ground state, we can drew the conclusion that the N-H and O=S band were elongated by forming the N-H...O=S type hydrogen bond, and the much stronger interaction caused the more obvious elongation. The vibration of N-H in hydrogen bond donor was changed obviously, and the infrared spectrum peak of N-H was enhanced and red shifted. The DPA-DMSO and ICPA-DMSO hydrogen bond complexes were excited to S2and S3state respectively, and the two states were both mainly contributed to the orbital transition from HOMO to LUMO. The electronic densities of all the orbitals for the hydrogen-bonded complexes are entirely localised on the DPA and ICPA monomer. Therefore, the DMSO acceptor kept its ground state. There is ππ*transition from HOMO to LUMO in DPA-DMSO frontier molecular orbital, and obvious intramolecular charge transfer in ICPA-DMSO complex.