• Rupert Bauer

      Articles written in Journal of Chemical Sciences

    • 1,1″,1‴-Trialkyl[4,2′;4′,4″;6′,4‴] quaterpyridinium trichlorides as electron transfer agents

      Rupert Bauer Klaus Hofstadler Christian Königstein

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      Photo- and electrochemical properties of a novel class of electron transfer substances (1,1″,1‴-trialkyl[4,2′;4′,4″;6′,4‴] quaterpyridinium trichlorides) have been studied for hydrogen producing systems containing sensitizerS, electron transfer agentR, electron donorD, and platinum catalyst. 1,1″,1‴-trimethyl [4,2′;4′,4″;6′,4‴] quaterpyridinium trichloride (1) and 1,1″,1‴-tribenzyl [4,2′;4′,4″;6′,4‴] quaterpyridinium trichloride (2) quench the excited state of Ru(bipy)3Cl2. Irradiation (λ>400 nm) of solutions containing Ru(bipy)3Cl2,1 or2 and EDTA lead to the formation of radicals of1 or2. A solution of radicals of compound1 can change its colour reversibly with change of pH-values (colourless in acidic, blue in alkaline solutions). Also, compounds1 and2 are able to produce H2 without additional sensitizer (irradiation light: λ>300 nm). Hydrogen production rates, quantum yields, and turnover numbers have been determined in two different systems (S, R, D, Pt, λ>400 nm; andR, D, Pt without additional sensitizer, λ>300 nm). Hydrogen production rates with compounds1 and2 are of the same order of magnitude as those with methyl viologen. The radicals of1 and2 are much more stable against oxygen, than those of methyl viologen. Cyclovoltammetry showed that the redox potentials of compounds1 and2 are dependent on pH: increasing pH values result in more negative redox potentials. Coulometric analysis showed that e.g. compound1 could accept 5 electrons at pH=4·8 and 3·4 electrons at pH=12·6 compared to only one electron for methyl viologen (independent of pH). This behaviour is explained with reference to protonated radicals.

    • Light-induced hydrogen production using waste compounds as sacrifical electron donors

      Christian Königstein Rupert Bauer

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      Systems for the conversion and chemical storage of solar energy are usually based on photo-induced electron transfer reactions from an excited sensitizer to an electron acceptor (i.e. an electron relay compound). We have investigated the photo- and electrochemical properties of two novel electron relay compounds: l,l″,r″′-trimethyl[4,2′; 4′,4″; 6′,4″′]quaterpyridinium trichloride (1) and 1,1′,1″,1″′-tetramethyl[4,2′; 4′,4′’; 6′,4″] quaterpyridinium tetrachloride (2). When solutions containing Ru(bpy)3Cl2 or Zn-porphyrin (as photosensitizer), compound1 or2 and EDTA (as sacrificial electron donor) are irradiated by visible light (λ > 400 nm), only the formation of reduced relay compound 1 occurs. Addition of platinum catalyst to such solutions with compound 1 leads to the formation of hydrogen. Quantum yields are in the range of 5%, calculated for absorbed light. Using other sacrificial electron donors such as alcohols or glucose (or waste compounds like 4-chlorophenol) did not result in hydrogen evolution. However,1 and2 are reduced by these sacrificial electron donors in the absence of an additional photosensitizer, when near UV irradiation light (λ > 280 nm) is used. Quantum yields for hydrogen production with compound1 are about 2%, calculated for absorbed light out of GC-measurements from H2 in the gas phase above the irradiated solution. The photo- and electrochemical properties of compounds1 and2 are discussed.

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