Electron and energy transfer within dyads involving polypyridyl-ruthenium(II) and -osmium(II) centres separated by rigid alicyclic bridges

Abstract

Rigid alicyclic frameworks (often referred to as molracs, relating to the molecular rack nature of the frame) have been used to vary the separation between organic electron-acceptor (quinone) moieties and chromophoric polypyridylruthenium() centres, and between metal centres in Ru-Ru and Ru-Os dinuclear complexes. Photophysical studies have allowed a preliminary insight into the effectiveness of such alicyclic structures in mediating intramolecular photoinduced energy and electron transfer. In the chromophore-spacer-quinone dyads, solventdependent quenching of the ruthenium() MLCT emission was observed and attributed to electron transfer processes. Distance and stereochemical dependencies of the quenching suggested that through-bond coupling was a factor in these systems. In the heterodinuclear systems, the photo-excited ruthenium() chromophore underwent intramolecular energy transfer to the osmium() component. A through-space Förster dipole-dipole mechanism could adequately account for the rate of the energy transfer process observed.

Photolysis of Fused Cyclobutatriazolines: An Adventitious Route to 3,6-Di(2-pyridyl)pyridazonorbornadiene

“…While derivatization of scaffold alkenes with the dipyridylpyridazine (dpp) ligand can be achieved in two steps by reaction of 3,6-di(2-pyridyl)-s-tetrazine (8) with alkenes, followed by aromatization with 2,3-dichloro-5,6dicyano-1,4-benzoquinone (ddq) (see Scheme 3), 8 attempts to adapt this protocol to the formation of the title 3,6-di(2pyridyl)pyridazine (2) by reaction with norborn-adiene (1) have been unsuccessful (see Scheme 2).…”

“…1,2 One strategy has been to proceed via norbornene reagents incorporating N,N-bidentate ligands, e.g. (2), since there has been much improvement in the methods for coupling norbornenes to form scaffold structures developed in our laboratory over the last few years.…”

“…(2), since there has been much improvement in the methods for coupling norbornenes to form scaffold structures developed in our laboratory over the last few years. [3][4][5] We have already shown that the norbornene reagent (5) containing the o-phenanthroline ligand can be prepared by the Diels-Alder addition of the cyclopentadienone (4) to norbornadiene (1). 6 Also, the diazafluorene reagent (7) is available in two steps by the 1,3-dipolar addition of diazodiazafluorene (6) to norbornadiene (1), followed by photochemical ejection of dinitrogen (Scheme 1).…”

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“…154 The rates of Ru?Os PEnT and Ru?quinone PET across rigid poly(norbornane) saturated bridges such as L 80 have been evaluated as a function of chromophore-quencher separation. 155 [(bipy) 2 Ru(m-L 81 )Rh III (bca) 2 ] 5+ can be attached to a TiO 2 electrode surface; absorption of light by the ruthenium fragment results in Ru?Rh PET and consequent injection of the electron from the transiently reduced rhodium centre into the semiconductor layer. Recombination between the ejected electron and Ru(III) is slow because of the distance involved.…”

Folding of a poly(oxyethylene) chain as probed by photoinduced energy transfer between Ru– and Os–polypyridine termini

“…4 Accordingly, very many dinuclear heterometallic complexes have been designed and investigated for the assessment of the role played by structural and electronic factors of the bridging ligand (BL) -which provides the covalent link between the photoactive termini -in controlling the energy-transfer process. [5][6][7][8] In general BLs containing unsaturated components are likely to mediate the transfer of excitation energy via a Dexter-type electron-exchange process, 9 whereas the use of saturated components within the BL only allows for the dipole-type, Förster mechanism, 10 which is typical of organic chromophores but may also occur for polypyridine complexes of Ru() and Os() and other metal centers.…”