Consequences of the One‐Electron Reduction and Photoexcitation of Unsymmetric Bis‐imidazolium Salts |
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Authors: | Verena Gierz Jascha Melomedov Dr. Christoph Förster Christine Deißler Dr. Frank Rominger Prof. Dr. Doris Kunz Prof. Dr. Katja Heinze |
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Affiliation: | 1. Institute of Inorganic Chemistry, Eberhard Karls‐University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen (Germany);2. Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg‐University of Mainz, Duesbergweg 10‐14, 55128 Mainz (Germany), Fax: (+49)?6131‐3927277;3. Institute of Organic Chemistry, Ruprecht Karls‐University of Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) |
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Abstract: | Coupling of uronium salts with in situ generated N‐heterocyclic carbenes provides straightforward access to symmetrical [ 4 ]2+ and unsymmetrical bis‐imidazolium salts [ 6 ]2+ and [ 9 ]2+. As indicated by cyclic and square‐wave voltammetry, [ 6 ]2+ and [ 9 ]2+ can be (irreversibly) reduced by one electron. The initially formed radicals [ 6 ].+ and [ 9 ].+ undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two‐electron reduction are the two carbenes. Upon irradiation with UV light both [ 6 ]2+ and [ 9 ]2+ emit at room temperature in solution but with dramatically different characteristics. The different fluorescence behavior is analyzed by emission spectroscopy and interpreted by using time‐dependent density functional calculations as largely due to different excited‐state dynamics of [ 6 ]2+ and [ 9 ]2+. The geometries of both radicals [ 6 ].+ and [ 9 ].+ and excited states {[ 6 ]2+} * and {[ 9 ]2+}* are substantially different from those of the parent ground‐state molecules. |
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Keywords: | bis‐imidazolium salts chromophores excited‐state dynamics photochemistry redox chemistry |
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