Heteroleptic bis-tridentate Fe(II)-NHC complexes as photobases

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Transition metal complexes, acting as photoacids or photobases, either upon direct excitation of a pendant (organic) photoacid / photobase motif by UV light or upon excitation of MLCT transitions in the visible part of the spectrum, have been reported in literature. However, almost no systematic ultrafast, mechanistic studies of noble-metal free transition-metal complex based photobases exist. Up to now, studies on quino¬line-based photobasicity are generally focused on molecular (full-organic) derivatives. Thus, this proposal aims at the synthesis and mechanistic characterization of new Fe(II)-NHC complexes as photobases that can be activated by visible light. The envisioned research combines (i) synthesis of new complexes and (ii) advanced spectroscopic characterization of excited-state proton transfer (ESPT) reactions underlying the photobasic action. We will investigate which intramolecular excited-state relaxation pathways in Fe(II)-NHC complex-based photobases compete with the envisioned photobasicity. Key to the in-depth mechanistic understanding targeted in this project is to understand possible excited-state specific ESPT reactivity from the solvent to the electronically excited photobasic complexes.