When Donors Turn into Acceptors: Ground and Excited State Properties of Fe<sup>II</sup> Complexes with Amine-Substituted Tridentate Bis-imidazole-2-ylidene Pyridine Ligands
Yannik Vukadinovic, Lukas Burkhardt, Ayla Päpcke, Anabel Miletic, Lorena Fritsch, Björn Altenburger, Roland Schoch, Adam Neuba, Stefan Lochbrunner, Matthias Bauer
Abstract
-heterocyclic carbene (NHC)-pyridine ligands is presented. In the homoleptic complexes imidazole-, methylimidazole-, or benzimidazole-2-ylidene, NHC donors are employed in combination with pyridine, functionalized in the 4-position by dimethylamine or dibenzylamine. The effects of these different functionalities on the electronic structure of the complexes are examined through detailed ground state characterization by NMR, single crystal X-ray diffraction, as well as electrochemical and spectroscopic methods. The net influence of these different functionalities on orbital-orbital and electrostatic ligand-iron interactions is investigated thoroughly by density functional theory, and changes in the excited state behavior and lifetimes are finally examined by ultrafast optical spectroscopy. Great deviations of the initially expected effects by substitution in 4-position on the photochemical properties are observed, together with a significantly increased π-acceptor interaction strength in the benzimidazole-2-ylidene functionalized complexes.