Photoinduced energy transfer in a rod-like dinuclear Ru(ii) complex containing bis-pyridyl-1,3,5-triazine ligands.

Three new rod-like dinuclear Ru(ii) polypyridine compounds have been prepared and characterized and their absorption spectra, redox behaviour and photophysical properties have been investigated, by conventional steady-state absorption and luminescence spectroscopic methods and by time-resolved methods operating in the nanosecond and femtosecond time regimes. All the new species contain 1,4-bis(2,2':6',2''-terpyridin-4'-yl)benzene () as bridging ligand and 2,4-bis(2-pyridyl)-6-p-bromophenyl-1,3,5-triazine and/or 4'-(p-bromophenyl)-2,2':6',2''-terpyridine as peripheral ligands. In particular, and are symmetric dyads since the Ru(ii) ions carry identical peripheral ligands (the triazine-based ligands in and the terpyridine-based ligands in the case of ), whereas is a non-symmetric dyad since its two Ru(ii) centers carry two different peripheral ligands (for the structural formulae of the compounds, see ). The absorption spectra and redox behaviour of the new compounds indicate, that each subunit of the dyads maintain its own peculiar properties in the dinuclear system, a requisite confirming the supramolecular nature of the systems. All the species exhibit metal-to-ligand charge-transfer (MLCT) emission, both at room temperature in fluid solution and at 77 K in rigid matrix. Luminescence lifetime and transient absorption spectroscopy reveal that efficient and fast photoinduced energy transfer takes place in the non-symmetric dyad from the subunit containing the terpyridine peripheral ligand to the subunit containing the triazine-based peripheral ligand. However, given the complexity of the transient spectra and the overlapping timescales of the processes of the symmetric and non-symmetric systems, any detailed analysis of the ultrafast results aimed at the identification of specific intercomponent energy transfer steps, and therefore to kinetically characterize the directional energy transfer, appears to be speculative.

Wiring terpyridine: approaches to alkynylthienyl 2,2':6',2''-terpyridines.

The reaction of triisopropylsilylethyne or trimethylsilylethyne with 4'-(5-bromo-2-thienyl)-2,2':6',2''-terpyridine () leads to 4'-(5-triisopropylsilylethynyl-2-thienyl)-2,2':6',2''-terpyridine () or 4'-(5-trimethylsilylethynyl-2-thienyl)-2,2':6',2''-terpyridine (). The latter compound may be deprotected to give 4'-(5-ethynyl-2-thienyl)-2,2':6',2''-terpyridine (). Treatment of the complexes [Ru()(2)][PF(6)](2), [Ru(tpy)()][PF(6)](2) and [Ru()(2)][PF(6)](2) ( = 4'-(4-bromo-2-thienyl)-2,2':6',2''-terpyridine) with triisopropylsilylethyne yields the corresponding homoleptic and heteroleptic alkynylthienyl-terminated ruthenium(ii) complexes, for which spectroscopic and electrochemical data are presented. The reaction of [RuCl(2)(DMSO)(4)] with leads to [Ru()(2)][PF(6)](2), in which the tpy ligands bear conjugated thienyl and alkynyl groups; the latter can also be accessed by deprotection of [Ru()(2)][PF(6)](2). The single-crystal structures of ligands and , and of [Ru()(tpy)][BPh(4)](2).1.3MeCN, [Ru()(2)][PF(6)](2).2MeNO(2), 2{[Ru()(2)][PF(6)](2)}.5MeCN, [Ru()(2)][PF(6)](2) and [Ru()(2)][PF(6)](2).MeCN are presented, and among the homoleptic complexes, pi-stacking interactions between thiophene and pyridine rings leading to pairs of associated cations provide a common structural motif.

[2,6-Bis(5-chloro-pyrimidin-2-yl-κN)pyri-dine-κN](2,2':6',2''-terpyridine-κN,N',N'')ruthenium(II) bis-(hexa-fluoridophosphate) acetonitrile disolvate.

In the title compound, [Ru(C(13)H(7)Cl(2)N(5))(C(15)H(11)N(3))](PF(6))(2)·2CH(3)CN, the Ru(II) atom is coordinated in a distorted octa-hedral geometry by a tridentate 2,2':6',2''-terpyridine ligand and a tridentate 2,6-bis-(5-chloro-pyrimidin-2-yl)pyridine ligand. Least-squares mean-plane distortions of only 1.72 (2) and 2.91 (2)° of the pyrimidyl rings with respect to the central pyridine are observed for the bis-(pyrimid-yl)pyridine-based tridentate ligand, while the distal pyridyl rings of terpyridine twist by 13.43 (7) and 4.68 (9)° away from the central pyridine ring.

Non-covalent polymerisation in the solid state: halogen-halogen vs. methyl-methyl interactions in the complexes of 2,4-di(2-pyridyl)-1,3,5-triazine ligands.

Fe(II), Co(II), Ni(II) and Cu(II) complexes based on the triazine ligand 2,4-di(2'-pyridyl)-6-(p-bromo-phenyl)-1,3,5-triazine have been synthesised and characterised. The electrochemical, magnetic and spectroscopic properties of the complexes have also been investigated, and the electron deficient triazine ligand has been shown to affect each of these properties. Further investigation of solid state structures of the ligand and its Fe(II), Co(II) and Cu(II) complexes has established that stabilising Br-Br interactions exist which link neighbouring molecules to form one-dimensional tapes. A slight modification of the ligand, i.e., using 2,4-di(2'-pyridyl)-6-(p-methylphenyl)-1,3,5-triazine, in which the phenyl substituent has changed from a bromine to a methyl group, eliminates the one-dimensional tape and gives rise to significant pi-stacking interactions in the solid state.

Tuning the excited-state energy of the organic chromophore in bichromophoric systems based on the Ru(II) complexes of tridentate ligands.

A series of new heteroleptic and homoleptic Ru(II) complexes containing variously substituted bis(pyridyl)triazine ligands has been prepared and their absorption spectra, redox behaviour and luminescence properties (both in fluid solution at room temperature and in a rigid matrix at 77 K) have been investigated. For some compounds, X-ray structures have also been determined. The new bis(pyridyl)triazines incorporate additional chromophores, such as biphenyl, phenanthrene, anthracene and bromoanthracene derivatives, so the Ru(II) species can be considered as multichromophoric species. The absorption spectra and redox properties of all the metal complexes have been assigned to features belonging to specific subunits, thus suggesting that these species can be regarded as multicomponent, supramolecular assemblies from an electronic coupling point of view. Whereas most of the complexes exhibit luminescence properties that can be attributed to metal-to-ligand charge-transfer (MLCT) states involving the metal-based subunit(s), the species containing the anthryl and, even more, the brominated anthryl chromophores exhibit complicated luminescence behaviour. For example, 2 d (the anthryl-containing heteroleptic metal compound) exhibits MLCT emission at room temperature and emission from the anthracene triplet at 77 K; 2 e (the bromo-substituted anthryl-containing heteroleptic metal compound) exhibits anthryl-based emission at 77 K and MLCT emission at room temperature, but with a prolonged lifetime, thus suggesting equilibration between two triplet states that belong to different chromophores. The equilibration regime between MLCT and aromatic hydrocarbon triplet states is therefore reached by suitable substitution on the organic chromophore.

Minimal structural reorganisation in the electrochemical oxidation of a dinuclear, double helical Cu(I) complex of a triazine-based pentadentate ligand.

A dicopper(I) double helicate oxidizes and rapidly reorganises to form a stable pentadentate dicopper(II) double helicate due to the proximity of pendant pyridyl rings as studied by electrochemical and structural analyses.

Designing tridentate ligands for ruthenium(II) complexes with prolonged room temperature luminescence lifetimes.

Coordination complexes have been used extensively as the photoactive component of artificial photosynthetic devices. While polynuclear arrays increase the probability of light absorption, the incorporation of the stereogenic Ru(2,2'-bipyridine)(3)(2+) motif gives rise to diastereomeric mixtures whereas the achiral Ru(2,2':6',2"-terpyridine)(2)(2+) motif creates stereopure polynuclear complexes. Thus, polynuclear arrays composed of ruthenium(II) complexes of tridentate ligands are the targets of choice for light-harvesting devices. As Ru(II) complexes of tridentate ligands have short excited state lifetimes at room temperature (r. t.), considerable effort has been focused on trying to increase their r. t. luminescence lifetime for practical applications. This tutorial review will report on the sophisticated synthetic strategies currently in use to enhance the room temperature photophysical properties of Ru(II) complexes of tridentate ligands.

Ruthenium complexes of easily accessible tridentate ligands based on the 2-aryl-4,6-bis(2-pyridyl)-s-triazine motif: absorption spectra, luminescence properties, and redox behavior.

A family of tridendate ligands 1 a-e, based on the 2-aryl-4,6-di(2-pyridyl)-s-triazine motif, was prepared along with their hetero- and homoleptic Ru(II) complexes 2 a-e ([Ru(tpy)(1 a-e)](2+); tpy=2,2':6',2"-terpyridine) and 3 a-e ([(Ru(1 a-e)(2)](2+)), respectively. The ligands and their complexes were characterized by (1)H NMR spectroscopy, ES-MS, and elemental analysis. Single-crystal X-ray analysis of 2 a and 2 e demonstrated that the triazine core is nearly coplanar with the non-coordinating ring, with dihedral angles of 1.2 and 18.6 degrees, respectively. The redox behavior and electronic absorption and luminescence properties (both at room temperature in liquid acetonitrile and at 77 K in butyronitrile rigid matrix) were investigated. Each species undergoes one oxidation process centered on the metal ion, and several (three for 2 a-e and four for 3 a-e) reduction processes centered on the ligand orbitals. All compounds exhibit intense absorption bands in the UV region, assigned to spin-allowed ligand-centered (LC) transitions, and moderately intense spin-allowed metal-to-ligand charge-transfer (MLCT) absorption bands in the visible region. The compounds exhibit relatively intense emissions, originating from triplet MLCT levels, both at 77 K and at room temperature. The incorporation of triazine rings and the near planarity of the noncoordinating ring increase the luminescence lifetimes of the complexes by lowering the energy of the (3)MLCT state and creating a large energy gap to the dd state.