Intermediate exciton spectrum

Figure 3.9. The Fourier transform of spectra of Fig. 3.8 Projection PK(a>) of the pure excitonic state on the eigenstates of the coupled system of an exciton K and the effective photon continuum in a 2D lattice, for various values of the wave vector K (KXd). The vertical peak represents a discrete state, whose weight is represented by a rectangle (a-d). For an exciton with K < K0, the continuum band (matter-contaminated photons) dominates the spectrum, with a quasi-lorentzian resonance (a,/). For K > K0, the discrete state dominates (d,e). In the intermediate region (b, c) the spectrum reflects the complicated behavior of its Fourier transform cf. Fig. 3.8. 

Figure 6 shows UV-vis-NIR spectra of solutions of ES-HCSA in w-cresol with deficient and excess HCSA dopants. For deficiently doped PANI-ES, the UV-vis-NIR spectrum (Fig. 6a) indicates that even 20% doping is enough to eliminate the characteristic chromophore of EB exciton transition at 633 nm and to promote partial delocalization of polarons as indicated by the appearance of a free carrier tail in the IR region. For the fully doped PANI-ES, the UV-vis-NIR spectrum (Fig. 6b) shows only a peak at —440 nm and a steadily increasing free carrier tail extended to the IR region, which is consistent with an extended conformational structure for the polymer chains. However, when PANI is overdoped (Fig. 6c), the polymer chains possess an intermediate conformation that is less expanded than that of the fully doped PANI-ES, as seen from the decreasing free carrier tail with an absorbance maximum centered at —1000 nm. 

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