Photoinduced Electron Transfer in Amino Acid Assemblies
The preparation and photophysical characterization of a series of redox-active lysines and related model compounds based on polypyridyl ruthenium complexes are described. Donor-chromophore-acceptor triad 1, [PTZpn-Lys(RuIIb2m)2+-NH-prPQ2+] (PF6−)4 (see below), was prepared by assembly of a modified ruthenium bipyridyl chromophore (RuIIb2m, where b = 2,2′-bipyridine, m = 4′-methyl-2,2′-bipyridyl-4′-carbonyl), an electron donor (phenothiazine, PTZ), and an electron acceptor (paraquat, PQ2+) on a lysine (Lys) scaffold utilizing amide bonds. This derivatized amino acid exhibited efficient (>95%) quenching of the ruthenium metal-to-ligand charge-transfer (MLCT) excited state upon irradiation with a 420-nm laser pulse in CH3CN. The resulting redox-separated state, [(PTZpn·+)-Lys(RuII,b2m)2+-NH-(prPQ·+)], stored 1.17 eV and lived for 108 ns (k = 9.26 × 106 s−1) as observed by transient absorption spectroscopy. Also studied was a series of related model systems that included model chromophores, simple chromophore-quencher dyads linked by amide bonds, and chromophore-quencher dyads based on lysine. An account of the kinetic behavior of these systems including triad 1 and a discussion of factors that influence the lifetime of the redox-separated states, their efficiency of formation, and their energy storage ability are presented. © 1993, American Chemical Society. All rights reserved.
Mecklenburg, SL; Peek, BM; Schoonover, JR; McCafferty, DG; Wall, CG; Erickson, BW; Meyer, TJ
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