Spectroscopy and defect states in polyaniline

Abstract

We report the far-infrared through visible photoinduced absorption (PA) spectra of polyaniline in the emeraldine-base and leucoemeraldine-base forms. The direct-absorption spectrum of emeraldine base (EB) has a broad absorption centered at 2 eV (the "exciton" band) and an absorption band at-3.6 eV (the m.-~* band gap). The PA spectra of EB for pumping into the "exciton" band and across the band gap are nearly identical, indicating the same types of charged defect states are created upon photoexcitation. The direct absorption spectrum of leucoemeraldine base (LB) shows only the~-m* band-gap absorption at-3.6 eV. For pumping into this absorption band, the PA spectrum of LB is very similar to that of EB, although important differences result from the lack of quinoid structures in this material. Based on our results, we propose a model for the photocreation of defect states in leucoemeraldine base and emeraldine base. The central roles of phenyl-ring rotations and of massive polarons are discussed.

A suitable model for emeraldine salt

“…In the case of EB phase, the experimental photoemission spectrum shows two transitions: 29,30 ͑a͒ A strong absorption centered at 2 eV and ͑b͒ an absorption band ͑the → * band gap͒ at 3.6 ͑solution͒ or 3.8 eV ͑film͒. Our PBEh calculations ͑see Fig.…”

Kinetic Mass of RT-BO Defect States in a Pernigraniline-Base Polymer

“…RT relaxation dominates the effective mass of coupled defects. Experimentally, very small infrared active vibration modes indicate a large polaron mass [11,12]. Our theory showed the origin of the large defect mass.…”

Electronic Phenomena in Polyanilines

“…This absorption is associated with a ring rotation polaron trapped adjacent to a quinoid ring. This trapped ring rotation polaron is readily observed in the photoexcitation spectra of emeraldine base [24,33]. Comparison of the magnitude of the photoinduced ir active vibrations and electronic absorption confirms the large mass of the photoexcited defects.…”

“…Photoexcitation of LEB films and powders with superbandgap light leads to new intragap absorptions centered at 0.7 eV and 2.9 eV [24,33]. This photoinduced absorption has been described in terms of formation of a ring rotation polaron [24][25][26]33.…”