Spectral range, conjugated polymers

As already shown, the sensitized spectra follow the dye absorption. Most of the dyes have sufficiently narrow absorption bands. This does not permit us to obtain the panchromatic sensitivity in the sufficiently broad spectral range. It was proposed to use the polymers with conjugated bonds as sensitizers [21]. The broad diffuse absorption spectra are inherent to such compounds. One can expect higher thermal stability from such sensitizers. In addition the application of binder may be omitted from the preparation of the photosensitive layers, for example, in electrophotography. Polymers with triple bonds, polyphenylenes and polyoxiphenylenes were used as sensitizers [10, 14, 278-280]. The typical results are shown in Fig. 47. The main rules for photoconductivity sensitized by polymers were the same as for the dyes. Optimum sensitization was obtained at the concentration of the sensitizer of 10 1-10-2 g/cm3 relative to the polymeric photoconductor weight. 

From TPA and EA spectra in soluble derivatives of PT and PPV polymers, we know that mAg is about 0.8 eV higher than 1B [34,55]. We therefore expect the Xi transition to be in the mid-lR spectral range, at about 0.8 eV or higher due to the exciton relaxation energy. The BX level, on the other hand, has not as yet been directly identified in ir-conjugated polymers, although a weak two-photon state, termed as fcAg was identified in recent nonlinear optical spectroscopy [56,57]. 

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