Active repair of a dinuclear photocatalyst for visible-light-driven hydrogen production.

The molecular apparatus behind biological photosynthesis retains its long-term functionality through enzymatic repair. However, bioinspired molecular devices designed for artificial photosynthesis, consisting of a photocentre, a bridging ligand and a catalytic centre, can become unstable and break down when their individual modules are structurally compromised, halting their overall functionality and operation. Here we report the active repair of such an artificial photosynthetic molecular device, leading to complete recovery of catalytic activity. We have identified the hydrogenation of the bridging ligand, which inhibits the light-driven electron transfer between the photocentre and catalytic centre, as the deactivation mechanism. As a means of repair, we used the light-driven generation of singlet oxygen, catalysed by the photocentre, to enable the oxidative dehydrogenation of the bridging unit, which leads to the restoration of photocatalytic hydrogen formation.

Ruthenium polypyridine complexes of tris-(2-pyridyl)-1,3,5-triazine-unusual building blocks for the synthesis of photochemical molecular devices.

The mononuclear compounds bis-(2,2'-bipyridine)ruthenium(ii)-(tris(2-pyridyl)triazine) [(bpy)(2)Ru(tpt)](PF(6))(2) and bis-(4,4'-di-tert-butyl-2,2'-bipyridine)ruthenium(ii)-(tris(2-pyridyl)triazine) [(tbbpy)(2)Ru(tpt)](PF(6))(2) have been synthesised and fully characterised. The attempted syntheses of heterodinuclear complexes with the tris(2-pyridyl)triazine (tpt) ligand as bridging ligand and various palladium(ii)- and platinum(ii)-dichloro complexes using the ruthenium complexes as starting materials resulted in a partial hydrolysis of the triazine based bridging ligand in case of and an unselective decomposition in case of . Compound reacts with Pd(DMSO)(2)Cl(2) and Pt(DMSO)(2)Cl(2) substituting three ligands from the metal centres of these precursors with partial hydrolysis of the triazine moiety of the bridging ligand yielding the dinuclear complexes bis-(4,4'-di-tert-butyl-2,2'-bipyridine)ruthenium(ii)-N-((picolinamido)(pyridin-2-yl)methylene)picolinamide)chloro-palladium(ii) [(tbbpy)(2)Ru(tptO)PdCl](PF(6))(2) and bis-(4,4'-di-tert-butyl-2,2'-bipyridine) ruthenium(ii)-N-((picolinamido)(pyridin-2-yl)methylene)picolinamide)chloro-platinum(ii) [(tbbpy)(2)Ru(tptO)PtCl](PF(6))(2). The newly formed bridging ligand coordinates in a bidentate fashion at the ruthenium centre and acts as a tridentate ligand for the second metal centre. The structures of all the complexes have been fully characterised and their photophysical properties are reported. A similar reaction sequence using the (4'-(p-bromophenyl)-2,2':6',2''-terpyridine)ruthenium(ii)-(tris(2-pyridyl)triazine) complex [(BrPhtpy)Ru(tpt)](PF(6))(2) and Pd(CH(3)CN)(2)Cl(2) as starting materials did not yield the hydrolysed bridging ligand but the expected dinuclear complex [(BrPhtpy)Ru(tpt)PdCl(2)](PF(6))(2) suggesting that the coordination of two pyridine rings of the tpt by the ruthenium centre is essential for the stabilisation of the tpt frame work. Preliminary investigations show that the dinuclear ruthenium-palladium and -platinum complexes are not active catalysts in the light-driven hydrogen production.

Ruthenium(II) complexes with improved photophysical properties based on planar 4'-(2-pyrimidinyl)-2,2':6',2' '-terpyridine ligands.

A series of new tridentate polypyridine ligands, made of terpyridine chelating subunits connected to various substituted 2-pyrimidinyl groups, and their homoleptic and heteroleptic Ru(II) complexes have been prepared and characterized. The new metal complexes have general formulas [(R-pm-tpy)Ru(tpy)]2+ and [Ru(tpy-pm-R)2]2+ (tpy = 2,2':6',2' '-terpyridine; R-pm-tpy = 4'-(2-pyrimidinyl)-2,2':6',2' '-terpyridine with R = H, methyl, phenyl, perfluorophenyl, chloride, and cyanide). Two of the new metal complexes have also been characterized by X-ray analysis. In all the R-pm-tpy ligands, the pyrimidinyl and terpyridyl groups are coplanar, allowing an extended delocalization of acceptor orbital of the metal-to-ligand charge-transfer (MLCT) excited state. The absorption spectra, redox behavior, and luminescence properties of the new Ru(II) complexes have been investigated. In particular, the photophysical properties of these species are significantly better compared to those of [Ru(tpy)2]2+ and well comparable with those of the best emitters of Ru(II) polypyridine family containing tridentate ligands. Reasons for the improved photophysical properties lie at the same time in an enhanced MLCT-MC (MC = metal centered) energy gap and in a reduced difference between the minima of the excited and ground states potential energy surfaces. The enhanced MLCT-MC energy gap leads to diminished efficiency of the thermally activated pathway for the radiationless process, whereas the similarity in ground and excited-state geometries causes reduced Franck Condon factors for the direct radiationless decay from the MLCT state to the ground state of the new complexes in comparison with [Ru(tpy)2]2+ and similar species.

3-Phenyl-6-(2-pyrid-yl)-1,2,4,5-tetra-zine.

The title compound, C(13)H(9)N(5), is the first asymmetric diaryl-1,2,4,5-tetra-zine to be crystallographically characterized. We have been inter-ested in this motif for incorporation into supra-molecular assemblies based on coordination chemistry. The solid state structure shows a centrosymmetric mol-ecule, forcing a positional disorder of the terminal phenyl and pyridyl rings. The mol-ecule is completely planar, unusual for aromatic rings with N atoms in adjacent ortho positions. The stacking observed is very common in diaryl-tetra-zines and is dominated by π stacking [centroid-to-centroid distance between the tetrazine ring and the aromatic ring of an adjacent molecule is 3.6 Å, perpendicular (centroid-to-plane) distance of about 3.3 Å].