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

过渡金属络合物作为光酸或光碱，无论是在紫外光下直接激发悬挂式(有机)光酸/光碱基元，还是在光谱的可见部分激发MLCT跃迁，都已有文献报道。然而，基于贵金属-无过渡金属络合物的光碱的系统的超快、机理研究几乎还是空白。到目前为止，喹啉类化合物的光碱性研究主要集中在分子(全有机)衍生物上。因此，本研究旨在合成可被可见光激活的新型Fe(II)-NHC络合物，并对其机理进行表征。这项设想的研究结合了(I)新络合物的合成和(Ii)激发态质子转移(ESPT)反应的高级光谱表征。我们将研究基于Fe(II)-NHC络合物的光碱中哪些分子内激发态弛豫途径与预期的光碱性竞争。深入理解本项目所针对的机理的关键是了解从溶剂到电子激发的光碱性络合物可能的激发态特定的ESPT反应性。

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.