Synthesis and Characterization of a Trisheteroleptic Ru II ‐Based Molecular Switch

• Published in: Chemistry : a European journal 2014-11, Vol.20 (47), p.15426-15433
• Main Authors: Monczak, Katharina, Peuntinger, Katrin, Sorsche, Dieter, Heinemann, Frank W., Guldi, Dirk M., Rau, Sven
• Format: Article
• Language: English
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201403418

The synthesis of a trisheteroleptic ruthenium complex [Ru(tb)(dppz)(tmbiH 2 )][PF 6 ] 2 (tb=4,4′‐di‐ tert ‐butyl‐2,2′‐bipyridine, dppz=dipyrido[3,2‐a:2′,3′‐c]phenazin, tmbiH 2 =5,6,5′,6′‐tetramethyl‐2,2′‐bibenzimidazole) is described. In addition, the structural characterisation by means of 1D, 2D 1 H NMR spectroscopy, and mass spectrometry, along with determination of the solid‐state structure of the important precursor Ru(tb)(dppz)Cl 2 , supports the proposed octahedral coordination geometry. The capability of tmbiH 2 to form hydrogen bonds is corroborated by the solid‐state structure. The photochemical characteristics of this complex can be described as a combination of the “light switch” effects, which are either attributed to the dppz or to the tmbiH 2 ligand. To illustrate the molecule’s double switchable features, steady‐state absorption and emission measurements were performed, which include the determination of the quantum yield and the p K a values of the acidic protons of the tmbiH 2 ligand. Notably, the emission lifetimes are sensitive to the solvents used. This phenomenon is due to a proton‐coupled deactivation of the excited metal‐to‐ligand charge transfer (MLCT) state of the complex.