Photoinduced Electron Transfer between Metal-Coordinated Cyclodextrin Assemblies and Viologens

Abstract

Two novel tris(bipyridine)ruthenium(ii) complexes bearing two and six b-cyclodextrin binding sites on their ligands have been synthesised and characterised. Complex 1, bearing two cyclodextrins, adopts a conformation in aqueous solution where parts of the aromatic ligands are self-included into the cyclodextrin moieties. This results in a loss of symmetry of the complex and gives rise to a much more complicated 1 H NMR spectrum than expected. Photophysical studies indicate that the appended cyclodextrins protect the luminescent ruthenium core from quenching by oxygen, which results in longer excited state lifetimes and higher emission quantum yields compared with the reference compound, the unsubstituted ruthenium tris(bipyridine). Inclusion of suitable guests such as dialkyl-viologens leads to a quenching of the luminescence of the central unit. In these supramolecular donor ± acceptor dyads an efficient pho-toinduced electron transfer from the excited ruthenium moiety (the donor) to the viologen unit (the acceptor) is observed. The alkyl chain length of the acceptor plays an important role on the binding properties; when it exceeds a certain limit the binding becomes strong enough for electron transfer to occur. Interestingly, a viologen with only one long alkyl tail instead of two shows no efficient quenching; this indicates that cooperative interactions between two cyclodextrins binding one viologen are essential to raise the binding constant of the supramolecular dyad.

Visible Light-Driven Water Oxidation Promoted by Host–Guest Interaction between Photosensitizer and Catalyst with A High Quantum Efficiency

“…16 On the other hand, the picoline ligands in [Ru(bda)(pic) 2 ] were replaced with more hydrophobic 4-phenylpyridine (ppy) to obtain a catalyst [Ru(bda)(ppy) 2 ] (1). The molecular structures of [CD-Ru(bpy) 3 ] 2+ and complex 1 are shown in Figure 1, and they were fully characterized by NMR, ESI-MS, and elemental analysis.…”

A Tris(bipyridine)ruthenium(II)–β‐Cyclodextrin Derivative: Synthesis, Luminescent Properties, and Application in Electrochemiluminescence DNA Sensors

“…The tris(bpyRu)-b-CD trace (curve a) shows a strong characteristic metal-ligand charge transfer (MLCT) centered at 458 nm and ligand-centered (LC) absorptions at 291 nm, corresponding to those of [Ru(bpy) 3 Cl 2 ] at approximately 451 and 287 nm (curve b), respectively. [9] Further-more, the maximum MLCT absorption intensity of tris(bpyRu)b-CD is 0.569, which is significantly higher than that of [Ru-(bpy) 3 Cl 2 ] (A 451 nm = 0.158). However, the MLCT transition of tris(bpyRu)-b-CD at 458 nm shows a slight redshift compared with that of [Ru(bpy) 3 Cl 2 ] at approximately 451 nm, which can be attributed to the influence of the electron-withdrawing amide groups on the ligands of tris(bpyRu)-b-CD.…”

Molecular recognition of aliphatic oligopeptides by aromatic diamine-bridged bis(β-cyclodextrin)

“…As a recently developing family of CD derivatives, bridged bis(b-CD)s have been known to alter significantly the molecular binding ability and selectivity toward a variety of guests in comparison with native and monomeric CDs, through the cooperative binding of a single model substrate by two hydrophobic cavities located in close vicinity [8,9]. Hence, the molecular recognition of substrate (guest) by bis(b-CD)s with a functional linker group becomes one of the most crucial current topics in supramolecular chemistry and biochemistry [10][11][12][13][14][15][16]. Among the various families of organic and biological guests for these studies, aliphatic oligopeptides have attracted considerable interest because they represent an intermediate step toward the recognition of protein surfaces, and the short peptide sequences are themselves worthwhile targets for recognition due to their potential applications in separation, diagnostic, or biological areas [17][18][19][20].…”