Ruthenium Polypyridine Complexes. On the Route to Biomimetic Assemblies as Models for the Photosynthetic Reaction Center

Abstract

We describe in this Account the preparation of RuL(3) complexes and their significance as biomimetic models for the photosynthetic reation center. Their preparation from simple or more complicated bypyridine ligands L and their photophysical data, especially their stability, are reported. Biomimetic models involving three concepts of the interaction of RuL(3) with acceptors in coordinatively, mechanically, or covalently linked supramolecular assemblies are also presented. The electron transfer (ET) of the noncovalently linked assemblies of RuL(3) complexes carrying polyether chains with one or two anisyl binding sites (4 or 5) with the cyclic bisviologen was studied. Molecular modeling and NMR titration clearly show the formation of supramolecular assemblies. Time-resolved spectroscopy demonstrated that ET and charge separation in the RuL(3) complexes with two binding sites are more efficient. The more constrained RuL(3)-bisviologen-catenane (6) possesses two conformations which exhibit different efficiency in ET, creating a charge-separated state in the microsecond domain. The covalently linked Ru(bpy)(3)(2+)-viologen assemblies having one (7, diad) or two bisviologen arms (8, diad) result in efficient ET. Addition of linear polyethers, cyclic polyethers, or crowns generates new triads and tetrads of the pseudorotaxane type. Molecular modeling and NMR titration clearly indicate the formation of supramolecular assemblies. The analysis of time-resolved studies proves fast ET and especially long-lived charge-separated states in these pseudorotaxanes. These data, compared with the findings for the photosynthetic reation center, show conclusive results. The lifetimes of the charge-separated states increase clearly in the sequence for noncovalently < mechanically < and covalently linked assemblies.

Photoinduced Processes within Compact Dyads Based on Triphenylpyridinium‐Functionalized Bipyridyl Complexes of Ruthenium(II)

“…Removal of bridging insulators (spacers) to extend molecular rigidity was anticipated to be at the expense of an undesirable increase of the intercomponent electronic coupling, usually withdrawn by the use of saturated-but often flexible-spacers such as methylene fragments. [11,12] However, in the present case, the selected 2,4,6-triphenylpyridinium (H 3 TP + ; Figure 1) electron-acceptor group (A) owns the great asset of possessing two bulky phenyl substituents ortho to the N pyridinio atom connected to P. These rings are likely to prevent the pyridinium from adopting a coplanar conformation with the covalently linked photosensitizer, as for instance in the case of 1-tpy ( Figure 1). [10] This pronounced steric hindrance, localized around the P-A linkage, is assumed to warrant the disruption of the conjugation between the connected subunits.…”

“…To circumvent this drawback, we reasoned that the adverse contribution of electronic coupling could be counterbalanced by using a primary light-triggered electron-donor (*P) stronger than *[Ru(tpy) 2 ] 2 + , namely the archetypal ruthenium(ii)-tris-bipyridyl complex. [11,15] It is thus expected that, despite the noticeable intramolecular interaction, the excited-state reducing strength of P will remain strong enough to initiate the transient reduction of A. Another advantage that could be taken of such a replacement stems from the fact that 0-bpy is a much greater luminophore than 0-tpy, thus making the photophysical study easier to carry out.…”

Synthesis, crystal structure determination, spectroscopic and electrochemical studies of trans-[Ru(PPh3)2(bbpH2)Cl]Cl·CHCl3·H20 (bbpH2=2,6-bis(benzimidazolyl) pyridine) – an infinite double columnar supramolecule in the solid state

“…Thus, the luminescence behavior of (1) is similar to that of [Ru(terpy) 2 ] 2+ , but different from that of [Ru(bbpH 2 ) 2 ] 2+ . (5) [Ru(terpy) 2 ] 2+ 1.28 c (6) [Ru(bpy) 3 ] 2+ 1.27 d (7) [Ru(bpy) 2 (BibzImH 2 )] 2+ 1.12 d (8) [Ru(bpy)(BibzImH 2 ) 2 ] 2+ 0.91 d (9) [Ru(BibzImH 2 ) 3 ] 2+ 0.80 d (10) [Ru(BiImH 2 ) 3 ] 2+ 0.54 d (11) [Ru(bpy)(BiImH 2 ) 2 ] 2+ 0.80 d (12) [Ru(bpy) 2 …”

“…The most extensively studied [1][2][3][4][5][6][7][8] ligand systems include the imine nitrogens as part of pyridine rings; e.g. bipyridine and phenanthroline and their derivatives.…”

Applications of X-Ray Transient Absorption Spectroscopy in Photocatalysis for Hydrogen Generation

“…The MLCT transitions of metal complexes are due to d ! p à transitions, shifting electron density from the metal to the ligands, which is the basis for employing these complexes as building blocks in artificial photosynthetic and photocatalytic systems for water splitting [109][110][111][112]. Due to the MLCT transitions, the metal-center oxidation states will change, accompanied by changes in coordination geometry and bond distance, all of which can be probed by XTA.…”