This paper will describe our recent efforts toward understanding the influence of structure on the excited state kinetics of heteroleptic phenanthroline (HETPHEN) Cu(I)diimine complexes. Toward this end, we have synthesized and fully characterized the ground and excited state kinetics of a series of CuHETPHEN model complexes. Analysis of the crystal structure of CuHETPHEN complexes bearing the commonly used blocking ligand 2,9-(2,4,6-trimethylphenyl)-1,10-phenanthroline shows a distorted tetrahedral environment around the Cu(I) center and strong inter-ligand interaction. Variation of the 2,9-substitution on the second phenanthroline ligand results in a wide span of triplet excited state lifetimes, from ~700 ps to over 70 ns in acetonitrile. A new blocking ligand, 2,9-(2,4,6-tri-isopropyl-phenyl)-1,10-phenanthroline was synthesized and used in the preparation of model CuHETPHEN complexes. The increase in steric bulk also enforces a distorted tetrahedral geometry around the Cu(I) center, but prevents any inter-ligand interaction. Notably, the CuHETPHEN model complexes are all relatively strong excited state reductants, with potentials ~-1.2V vs. SCE. The mononuclear CuHETPHEN complexes are currently being used to build linked bimetallic complexes and electron donor-acceptor dyads. We anticipate that these results will contribute to the design of CuHETPHEN complexes with long-lived triplet states to facilitate intra- and intermolecular charge transfer, charge accumulation, and catalysis.

Tuning triplet excited state lifetimes in CuHETPHEN complexes

254th National Meeting (2017)

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