RuII polyimine complexes have been widely studied as photosensitizers due to their intense metal-to-ligand charge transfer (MLCT) transition. In contrast, their abundant and environmentally benign congeners, FeII, have received little attention. Such a discrepancy lies in the fact that the energy splitting between the t2g and eg orbitals in FeII is much less than that in RuII when ligated identically. Therefore, the photochemically reactive 3MLCT state is usually deactivated in unity yield by low-lying metal-centered states in common FeII polyimine complexes.1 Recently, we demonstrated effective suppression of such deactivation using strongly donating tridentate N-heterocyclic carbene (NHC) ligands, resulting in elongated 3MLCT lifetime from 150 fs to 9 ps.2 By subtle manipulation of the ligand energy level, the 3MLCT lifetime can be further increased to 20 ps. This implies great prospects of sensitizing TiO2 with novel FeII NHC complexes, which is now being actively conducted in our group. In parallel, we have constructed heteroleptic tris(bidentate) FeII NHC complexes from the perspective of more versatile functionalities.3 This also delivered an 3MLCT lifetime as long as 16 ps. Further chemical modification is now on the way, aiming at fitting the sophisticated Fe NHC chemistry to the earnest expectation for photochemically valuable FeII? compounds.References 1 A. Cannizzo, et al. Coord. Chem. Rev., 2010, 254 , 2677.2 Y. Liu, et al. Chem. Commun., 2013, 49 , 6412.3 Y. Liu, et al. To be submitted.

Towards harnessing solar energy with abundant iron(II) <i>N</i>-heterocyclic carbene complexes

248th National Meeting (2014)

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Towards harnessing solar energy with abundant iron(II) N-heterocyclic carbene complexes