A novel Ru(II) complex possessing two sequentially linked viologen units, Ru-V(1)-V(2)(6+), was synthesized and characterized. Upon excitation of the Ru(II) unit (lambda(exc) = 532 nm, fwhm approximately 10 ns), a long-lived charge-separated (CS) state is observed (tau = 1.7 micros) by transient absorption spectroscopy. Unlike Ru(bpy)(3)(2+), which cleaves DNA upon photolysis through the formation of reactive oxygen species, such as (1)O(2) and O(2)(-), the photocleavage of plasmid DNA by Ru-V(1)-V(2)(6+) is observed both in air and under N(2) atmosphere (lambda(irr) > 395 nm).

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A novel [2]catenane 1 incorporating 2,2'-bipyridine and cyclobis-(paraquat-p-phenylene) (BXV 4 ) was synthesized by self-assembly. X-ray analysis and molecular modeling revealed the structure of the ligand 1. The complexation of 1 within a ruthenium complex afforded a catenane-type artificial photosynthesis assembly 2, in which the sensitizer (Ru 2 center) and the acceptor (BXV 4 ) are linked noncovalently. Molecular modeling indicated that the catenane complex 2 has two main conformers with different sensitizer ± acceptor distances; its macrocyclic polyether unit is more extended than that in 1.

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The synthesis and photophysical properties of a ruthenium dyad (4) and triad (5) are reported. Both biomimetic systems are physical models for the photosynthetic reaction center. They consist of a ruthenium(II)-polypyridyl sensitizer featuring chemically attached 3,3‘-dimethyl-4,4‘-viologen and 4,4‘-viologen electron acceptors. The binding of the chemically attached electron acceptors by the three structurally different crown ethers, DB30C10, BBO5O5, and AAO5O5, offers a remarkable tool for the enhancement of the lifetimes of the charge separated states (τCS), up to a factor of 2 × 104. The drastic increase in the lifetimes observed can be explained by a decrease in the reorganization energy λ due to the presence of the crown ether units bound to the viologen acceptor.