Electronic processes in polyaniline films photoexcited with picosecond laser pulses: A three-dimensional model for conducting polymers

Abstract

Photoinduced absorption data for polyaniline films in two forms, emeraldine base (EB) and emeraldine salt (ES), are presented and discussed. Electrochemically synthesized films were excited with laser pulses of large intensity (the energy \ensuremath{\simeq}2 eV, the pulse duration \ensuremath{\simeq}8 ps, the pulse energy up to 10 mJ/${\mathrm{cm}}^{2}$). Optical spectra of the EB and ES films in the temperature range from 298 to 363 K are also studied. The polymer film is presumed to be a three-dimensional (3D) system of long finite conjugated fragments of polymer chains. Considering each fragment integrally and taking into account the electronic polarization energy (\ensuremath{\simeq}1.5 eV) for a charge in the film, the 3D model of a charge-transfer exciton is proposed. The low-energy absorption of EB and ES and the electronc processes in photoexcited films are interpreted within the framework of the proposed model, avoiding the commonly adopted approach of an isolated polymer chain.