Photophysics and Redox Behavior of Chiral Transition Metal Polymers

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Abstract
The absorption and emission spectra, excited-state lifetimes, quantum yields, and electrochemical measurements have been obtained for a new series of chiral complexes based on three different chiral 2,2‘:6‘,2‘ ‘-terpyridine ligands, (−)-ctpy, (−)-[ctpy-x-ctpy], and (−)-[ctpy-b-ctpy], with one, two, or multiple Ru metal centers. The room-temperature absorption and emission maxima of {[((−)-ctpy)Ru]-(−)-[ctpy-b-ctpy]-[Ru((−)-ctpy)]}(PF6)4 and ((−)-[ctpy-b-ctpy])-{[Ru((−)-[ctpy-b-ctpy])](PF6)2}n were shifted to lower energies and also exhibited significantly longer luminescence lifetimes when compared to [Ru((−)-ctpy)2](PF6)2, {[((−)-ctpy)Ru]-(−)-[ctpy-x-ctpy]-[Ru((−)-ctpy)]}(PF6)4, and ((−)-[ctpy-x-ctpy])-{[Ru((−)-[ctpy-x-ctpy])](PF6)2}n. In terms of their electrochemical behavior, all of the complexes studied exhibited one Ru-centered and two ligand-centered redox waves and the {[((−)-ctpy)Ru]-(−)-[ctpy-x-ctpy]-[Ru((−)-ctpy)]}(PF6)4, ((−)-[ctpy-x-ctpy])-{[Ru((−)-[ctpy-x-ctpy])](PF6)2}n, and ((−)-[ctpy-b-ctpy])-{[Ru((−)-[ctpy-b-ctpy])](PF6)2}n complexes were found to electrodeposit upon ligand-based reduction. The difference between the formal potentials of the Ru-centered and the first ligand-centered (least negative) waves corresponded linearly with the changes in the observed emission energies. The shifts in energy are discussed using a particle-in-a-box model, and the luminescence lifetimes are discussed in terms of the structure of the excited-state manifold.

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