Photoactive dopants

Since the photoconductive properties of poly(A-vinylcarbazole) (PVK) were revealed, carbazole-based polymeric materials have been extensively studied [264-266]. Recently, there has been a renewed interest in the study of photo-conductive polymer composites. Photoactive dopants capable of charge injection into the polymer matrix are normally employed. Of these photoactive dopants, C60 and CNTs as well as inorganic SCs have been shown to be among the most efficient to date [267]. 

On the other hand, the dopant ions can also act as recombination centers for photoelectrons and holes thus decreasing the photocatalytic performance (Dvoranova et al. 2002). The frequently reported decrease in photoactivity of metal-ion-doped Ti02 with increasing dopant concentration above a certain doping level is a good illustration of this phenomenon. In fact, visible-light photoactivity could hardly be... 

Therefore, significant improvement in the photoactivity is possible only at low dopant concentrations. It further activates the competitive processes on the photocatalyst surfaces, however, the exact involvement of these processes are still not known. The surface metal ion activates the carbon dioxide molecule in a different way as that of semiconductors, leading to a relatively high product yield compared to the bare photocatalyst. The earth s abundance and cost of the metals are the main problems which adversely affect the process economics, hence the metal doping increases the overall cost of the process. Hence the practical implementation is not possible with the metal doped photocatalyst even though it s a promising route for the conversion of carbon dioxide into chemical and fuels. 

Therefore we have developed an experimental setup which provides mid-IR spectroscopy on timescales from pico- to milliseconds. For the proof-of-princi-ple experiments an azo compound, i.e., diazo Meldrum s acid, was selected. This compound was used as dopant in a polymer matrix, allowing variation of the absorption strength of selected mid-infrared bands over of a wide range. The IR absorption bands of azo functional groups are additionally in a range where nearly no other IR bands are located (-2200 cm-1). Azo compounds are also structurally closely related to the triazene groups in our designed polymers and are classical representatives of photoactive compounds. 

The potential of microemulsion-derived titania gels as host matrices for photoactive ions and molecules was explored by Guizard et al. [94] with the dopants Eu , Nd " ", and pyrene. It was concluded that the gel matrix presented three types of host sites associated with the microporosity, the mesoporosity, and the macroporosity. 

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