Photoinduced absorption spectrum bleaching

Figure 15 shows the photoinduced absorption (bleaching) spectrum of the single crystals of all-... 

Recently, the results of photoinduced absorption studies (i.e. excitation spectroscopy) of the emeraldine base polymer have been reported.22-24 Photoinduced absorptions were observed23 24 t 0.9eV, 1.4eV and 3.0 eV, accompanied by photo-induced bleaching at 1.8eV and at energies above 3.5 eV. The 1.4 and 3.0 eV photoinduced absorptions have been interpreted, by analogy with the absorption spectrum of the emeraldine salt, to the photoproduction of polarons in emeraldine base.24 Stafstrom et al25 concluded that positive and negative polarons,as well as positive bipolarons account very well for the 1.4 and 3.0 eV photoinduced absorptions. No specific explanation has been proposed for the 0.9 eV photoinduced peak. 

The optical absorption of emeraldine base film, together with selected millisecond photoinduced absorption and long time photoinduced absorption results are shown in Fig. 7. The " steady state (ms) spectrum of emeraldine base has features indicative of both the ring rotation polaron (at 0.9 eV and 2.9 eV) and the ring rotation polaron bound to imine groups (1.4 eV and 2.9 eV) as well as bleaching of the tt-tt band (3.7 eV) [43]. At long times only the trapped polaron is observed [17,27]. 

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