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Influence of Multiple Protonation on the Initial Excitation in a Black Dye

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journal contribution
posted on 08.12.2011, 00:00 by Maria Wächtler, Stephan Kupfer, Julien Guthmuller, Jürgen Popp, Leticia González, Benjamin Dietzek
Solvent pH influences electronic and optical properties of photoactive systems by protonation/deprotonation of basic/acidic positions. In this study a joint experimental and theoretical approach is presented to analyze the acid/base properties of a new 4H-imidazole ruthenium(II) complex (Ru). The imidazole ligand is substituted by two dimethylamino groups and hence offers four positions for protonation. To identify the species present in certain acid concentration ranges calculated absorption and resonance Raman (RR) spectra are compared to experimental results. It is shown that three different protonated species can be prepared separately from each other by varying the acid concentration in solution and the character of the substituent can be switched from electron donating to electron withdrawing by protonation, which plays an important role in the further analysis of pH-dependent photoinduced processes in these systems.