Ru Polypyridine Complexes Research Articles

Formation of Assemblies Comprising Ru–Polypyridine Complexes and CdSe Nanocrystals Studied by ATR-FTIR Spectroscopy and DFT Modeling

The interaction between CdSe nanocrystals (NCs) passivated with trioctylphosphine oxide (TOPO) ligands and a series of Ru-polypyridine complexes-[Ru(bpy)(3)](PF(6))(2) (1), [Ru(bpy)(2)(mcb)](PF(6))(2) (2), [Ru(bpy)(mcb)(2)](BarF)(2) (3), and [Ru(tpby)(2)(dcb)](PF(6))(2) (4) (where bpy = 2,2'-bipyridine, mcb = 4-carboxy-4'-methyl-2,2'-bipyridine, tbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; dcb = 4,4'-dicarboxy-2,2'-bipyridine, and BarF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)-was studied by attenuated total reflectance FTIR (ATR-FTIR) and modeled using density functional theory (DFT). ATR-FTIR studies reveal that when the solid film of NCs is exposed to an acetonitrile solution of 2, 3, or 4, the complexes chemically bind to the NC surface through their carboxylic acid groups, replacing TOPO ligands. The corresponding spectral changes are observed on a time scale of minutes. In the case of 2, the FTIR spectral changes clearly show that the complex adsorption is associated with a loss of proton from the carboxylic acid group. In the case of 3 and 4, deprotonation of the anchoring group is also detected, while the second, "spectrator" carboxylic acid group remains protonated. The observed energy difference between the symmetric, ν(s), and asymmetric, ν(as), stretch of the deprotonated carboxylic acid group suggests that the complexes are bound to the NC surface via a bridging mode. The results of DFT modeling are consistent with the experiment, showing that for the deprotonated carboxylic acid group the coupling to two Cd atoms via a bridging mode is the energetically most favorable mode of attachment for all nonequivalent NC surface sites and that the attachment of the protonated carboxylic acid is thermodynamically significantly less favorable.

Effect of Electronic Structure on the Photoinduced Ligand Exchange of Ru(II) Polypyridine Complexes

The series of complexes [Ru(bpy)(2)(L)](2+), where bpy = 2,2'-bipyridine and L = 3,6-dithiaoctane (bete, 1), 1,2-bis(phenylthio)ethane (bpte, 2), ethylenediamine (en, 3), and 1,2-dianilinoethane (dae, 4), were synthesized, and their photochemistry was investigated. Photolysis experiments show that the bisthioether ligands in 1 and 2 are more easily photosubstituted by chloride ions, bpy, and H(2)O than the corresponding diammine complexes in 3 and 4 to generate the bis-substituted products. Electronic structure calculations show that bond elongation in the lowest energy triplet metal-to-ligand charge transfer ((3)MLCT) state compared to the ground state is greater for complexes containing bisthioether ligands than those with coordinated bidentate nitrogen atoms. This elongation in the excited state is attributed to Ru-S π-bonding character of the highest occupied molecular orbitals, which is not present in the diamine complexes. In the Ru→bpy (3)MLCT state, the lower electron density on the metal-centered highest occupied molecular orbital (HOMO) weakens the Ru-S bond and results in the greater photoreactivity of 1 and 2 relative to that of 3 and 4. The more efficient photoinduced ligand exchange of the complexes possessing thioether ligands results in binding of 1 and 2 to DNA upon irradiation.

The Frenkel exciton Hamiltonian for functionalized Ru(II)–bpy complexes

Electronic excitation energies and wavefunctions are calculated for Ru ( bpy ) 3 + 2 ( bpy = 2 , 2 ′ ‐ bipyridine ) and its two derivatives, where one or two bpy ligands are functionalized with carboxyl and methyl groups. We show that the structure of these molecules allows one to express their excitations in terms of wavefunctions localized on individual ligands via the Frenkel exciton model. The model is based on three parameters – effective single-ligand excitation energy, inter-ligand interaction coupling, and energy shift brought by the ligand functionalization – that are extracted from time-dependent density functional theory (TDDFT). This simple model is able to accurately explain the optical intensity, localization properties, and splitting patterns of the low-energy excited states not only in molecules with a high degree of symmetry, but also in non-symmetrically functionalized Ru(II) complexes in vacuum and in solvent. Such reduced description of the excited states provides better understanding and interpretation of experimental data on Ru–polypyridine complexes, and allows for description of excited-state structure in a large ensemble of interacting molecules and treatment of possible charge and energy transfer phenomena in the material.

Classification of novel thiazole compounds for sensitizing Ru–polypyridine complexes for artificial light harvesting

A systematic study of the Förster resonance energy transfer (FRET) efficiency between thiazole dyes and a ruthenium–polypyridine complex is presented. While ruthenium–polypyridines are conventionally used in artificial light harvesting systems as primary electron donors, their application suffers from rather low extinction coefficients in the visible spectral range and an absorption gap between the ππ ⁎ transitions of the ligands and the MLCT transitions. In this paper it is shown how thiazoles might help to circumvent theses issues. The absorption and emission spectra of the thiazole can be synthetically adjusted to fall into the absorption gap of the Ru dye and to efficiently overlap with the 1MLCT absorption of the complex, respectively. Thereby, the thiazoles might serve as antenna structures to funnel energy to the Ru-polypyridine unit, which finally can act as a photoactivated primary electron donor. Systematic investigations of the Förster radii of representative thiazole Ru-polypyridine dye pairs corroborate this potential quantitatively.

New star-shaped trinuclear Ru(ii) polypyridine complexes of imidazo[4,5-f][1,10]phenanthroline derivatives: syntheses, characterization, photophysical and electrochemical properties

A series of new star-shaped trinuclear Ru(II) complexes of imidazo[4,5-f][1,10]phenanthroline derivatives, [{Ru(bpy)(2)}(3){μ-mes(1,4-phO-Izphen)(3)}](ClO(4))(6)·4H(2)O (6), [{Ru(phen)(2)}(3){μ-mes(1,4-phO-Izphen)(3)}](ClO(4))(6)·3H(2)O (7), [{Ru(bpy)(2)}(3){μ-mes(1,2-phO-Izphen)(3)}](ClO(4))(6)·4H(2)O (8), and [{Ru(phen)(2)}(3){μ-mes(1,2-phO-Izphen)(3)}](ClO(4))(6)·3H(2)O (9) [mes(1,4-phO-Izphen)(3) (4) = 2,4,6-tri methyl-1,3,5-tris(4-oxymethyl-1-yl(1H-imidazo-2-yl-[4,5-f][1,10]phenanthroline)phenyl)benzene and (mes(1,2-phO-Izphen)(3) (5) = 2,4,6-trimethyl-1,3,5-tris(2-oxymethyl-1-yl(1H-imidazo-2-yl[4,5-f][1,10]phenanthroline)phenyl)benzene] have been synthesized and characterized. Their photophysical and electrochemical properties have also been studied. The core molecule, 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene (1) and the trialdehyde intermediate, 2,4,6-trimethyl-1,3,5-tris(4-oxymethyl-1-formylphenyl)benzene (2) are characterized by single crystal X-ray diffraction: triclinic, P1[combining macron]. The complexes 6-9 exhibit Ru(II) metal centered emission at 618, 601, 615, and 605 nm, respectively, in fluid solution at room temperature. The emission profile and emission maxima are similar and independent of the excitation wavelength for each complex. The complexes 6-9 undergo metal centered oxidation and the E(1/2) values for the Ru(II)/Ru(III) redox couples are 1.33, 1.34, 1.35, and 1.35 V versus Ag/Ag(+), respectively, which are cathodically shifted with respect to that of the mononuclear complex [Ru(bpy)(2)(PIP)](2+) (PIP = 2-phenylimidazo[4,5-f][1,10]phenanthroline). The study demonstrates the versatility of the highly symmetric trinucleating imidazo[4,5-f][1,10]phenanthroline-based core ligands 4 and 5 in forming trinuclear Ru(II) complexes.

Graphene oxide–Ru complex for label-free assay of DNA sequence and potassium ions via fluorescence resonance energy transfer

Herein using classic DNA binding Ru polypyridine complex and graphene oxide, we developed a label-free and simple method for fluorescence recognition of complementary double-stranded DNA and aptamer-based potassium ions detection processes.

Synthesis of polypyridyl ruthenium complexes with 2-(1-aryl)-1H-imidazo[4,5-f]-1,10-phenanthroline ligand and its application for luminescent oxygen sensing

Polypyridyl ruthenium (Ru) complexes 1–3 were prepared. Their photophysical properties were investigated by UV-Vis absorption and luminescence emission spectra. The luminescent lifetimes of these Ruthenium complex were prolonged by more than 5 folds (τ = 2.50 μs for complex 3) when compared with the parent Ru complex 1 (τ = 0.45 μs). We propose that the extended luminescent lifetime of complex 3 is due to the equilibrium between 3MLCT state and the pyrene localized 3π-π* triplet state (3IL). The luminescent O2-sensing property of the complexes in solution and the IMPEK-C polymer film were studied, and the O2 sensing was quantified with the two-site model. The oxygen-sensing property of the Ru complexes can be improved by 104-fold with extension of the luminescent lifetimes. For example, the quenching constant K SV was improved from 0.0023 Torr−1 of 1 to 0.2393 Torr−1 for 3. Our results demonstrated a versatile approach for the preparation of Ru (II) polypyridine complexes with extended luminescent lifetimes as functional materials, for example, for luminescent oxygen-sensing applications.

Ruthenium polyoxometalate water splitting catalyst: very fast hole scavenging from photogenerated oxidants

The tetraruthenium polyoxometalate water oxidation catalyst 1 performs very fast hole scavenging from photogenerated Ru(iii) polypyridine complexes, both in homogeneous solution and at a sensitized nanocrystalline TiO(2) surface.

Visible light-driven water oxidation catalyzed by a highly efficient dinuclear ruthenium complex

Visible light-driven water oxidation has been achieved by the dinuclear ruthenium complex 1 with a high turnover number of 1270 in a homogeneous system in the presence of a Ru polypyridine complex photosensitizer.

Electronic Excited‐State Engineering

The immense flow of sun power that hits the atmosphere, approximately 170000 trillion watts (170 PW), drives large scale natural processes such as photosynthesis, which are key to sustaining life in the biosphere. The conversion of solar light energy in the photosynthetic process is done by complex supramolecular architectures which convert the photon flux into chemical fuel. This operation is enabled by electronic excited states residing in the molecular subunits of photosynthetic systems. These systems accept, store and transfer the excitation energy in a concerted temporal and spatial sequence. In the last 20 years we have witnessed the development of supramolecular photochemistry. The assembly by design of synthetic molecular fragments having specific basic functions (e.g. light harvesting) to build up a supramolecular architecture capable of capturing photons and delivering a superior action (e.g. energy conversion, mechanical motion) is the basic concept of the discipline. This research can ultimately be viewed as a kind of electronic excited state engineering, in which chemists make and test supramolecular systems which deliver a specific action, but only when they are properly designed in terms of the excited state interactions among their components—as found in nature. Thus, a huge number of supramolecular photoactive systems, for example light-powered nanomachines or prototype artificial photosynthetic modules, have been prepared over the years. When engineering artificial photoactive supramolecular systems researchers are often puzzled by problems related to the improvement and/or tuning of the electronic properties of the molecules they wish to assemble. This challenging work may have to do, for instance, with the increase of absorption in a given spectral window, the tuning of the luminescence colour, or the prolongation of an excited-state lifetime. The last issue is particularly important because the duration of an electronic excited state largely dictates its final destiny, especially in supramolecular systems. In a seminal paper from 1992, Ford and Rodgers first reported that the luminescent metal-to-ligand-charge transfer triplet excited state (MLCT*) of a Rupolypyridine complex exhibits a prolonged lifetime (11-fold) when covalently linked to a pyrene fragment via a hydrocarbon chain. The reason for this unusual and potentially interesting behaviour is that the p-p triplet excited state of the pyrene unit (pp*) is lower-lying and almost isoenergetic to the MLCT* level of the Ru-complex moiety and, in solution at room temperature, they may undergo thermal equilibration upon MLCT*!pp* energy transfer followed by back-transfer of energy, as depicted in Figure 1. The lifetime prolongation relies on the temporary storage of the excitation energy on the long-lived pyrene triplet level, which practically acts as an energy reservoir, a role reminiscent of a hydroelectric basin. Eventually, this gives back the excess energy to the metal complex which undergoes delayed deactivation. The engineering concept of this photoactive dyad encompasses two crucial features: a) the reservoir lifetime (pyrene triplet) must be significantly longer than that of the Ru-based MLCT* level ; b) the thermal rate of energy back-transfer (kb in Figure 1) must be significantly faster

Comparison of Intra- vs Intermolecular Long-Range Electron Transfer in Crystals of Ruthenium-Modified Azurin

Selective metal-ion incorporation and ligand substitution are employed to control whether electrons tunnel over intra- or intermolecular separations in crystals of P. aeruginosa azurin modified with Ru-polypyridine complexes. Cu(1+)-to-Ru3+ electron transfer (ET) across a specific protein-protein interface in the crystal lattice has a time constant 5-10 times longer than ET between the same donor and acceptor within a single protein (tauET = 5 vs 0.5-1.0 micros). Slower intermolecular ET agrees well with a longer distance between redox centers across the inter-protein (18.9 A) compared to the intra-protein separation (17.0 A) and indicates that the closest donor/acceptor pair dominates crystal ET. Lowering the crystal pH accelerates inter-protein ET (tauET = 1.0 micros) but not intra-protein ET. Faster inter-protein ET likely results from a pH-induced peptide bond flip that perturbs hydrogen bonding in the path between Ru and Cu centers on adjacent molecules.

Photoinduced Charge Transfer between CdSe Nanocrystal Quantum Dots and Ru−Polypyridine Complexes

In this communication, we demonstrate a new approach to sensitization of Ru-polypyridine complexes by using semiconductor nanocrystal quantum dots (NQDs). When mixed in solution, the complexes functionalized by carboxylic groups adsorb onto the surface of the NQDs. Excitation of NQDs by 400 nm light leads to fast, 5 ps hole transfer from the photoexcited NQDs to the surface-adsorbed complexes. This result indicates that Ru complexes can be sensitized by CdSe NQDs, which opens interesting opportunities for designing new types of photocatalytic materials for solar energy conversion applications. These materials will take advantage of broad size-controlled absorption spectra and large extinction coefficients of NQDs as well as the unique property of NQDs to respond to absorption of a single photon by producing multiple electron-hole pairs.

Sensitization of Nanocrystalline TiO2 with Black Absorbers Based on Os and Ru Polypyridine Complexes

New metal complexes of the type [M(H3tcterpy)LY]+ (where M = Os(II) or Ru(II), L = substituted or unsubstituted bipyridine or pyridylquinoline, and Y = Cl-, I-, or SCN-) have been designed, synthesized, and characterized in view of their application for dye-sensitized solar cells (DSSCs). The Os dyes show a very broad absorption, and correspondingly, the DSSCs show an unprecedented spectral response in the NIR, with an onset at 1100 nm, reaching values of about 50% at 900 nm. The integrated photocurrent of some of such Os dyes is similar to that of the well-known [Ru(Htcterpy)(NCS)3](TBA) and superior to that of the [Ru(Hdcbpy)2(NCS)2](TBA)2 sensitizer. The Ru dyes show absorption and DSSC spectral response between those of the red and black dyes. Their advantage is their potential superior stability due to the reversible oxidative electrochemistry.

Luminescence of a New Ru(II) Polypyridine Complex Controlled by a Redox-Responsive Protonable Anthra[1,10]phenanthrolinequinone

Redox-controlled luminescence quenching is presented for a new Ru(II)-bipyridine complex [Ru(bpy)2(1)]2+ where ligand 1 is an anthra[1,10]phenanthrolinequinone. The complex emits from a short-lived metal-to-ligand charge transfer, 3MLCT state (τ = 5.5 ns in deaerated acetonitrile) with a low luminescence quantum yield (5 × 10-4). The emission intensity becomes significantly enhanced when the switchable anthraquinone unit is reduced to corresponding hydroquinone. On the contrary, chemical one-electron reduction of the anthraquinone moiety to semiquinone in aprotic tetrahydrofuran results in total quenching of the emission.

Photoinduced intra-molecular electron transfer in aniline-containing Ru(II) polypyridine complexes

The photoinduced intra-molecular electron transfer in three aniline-containing Ru(II) polypyridine complexes, [Ru(bpy) 2(bpy-bmam)](PF 6) 2 ( 2), Ru(dcbpy)(bpy-bmam)(NCS) 2 ( 3), and Ru(dcbpy)(bpy-mam)(NCS) 2 ( 4) (bpy-bmam=4,4′-bis( N-methyl-anilinomethyl)-2,2′-bipyridine, bpy-mam=4-methyl-4′-( N-methyl-anilinomethyl)-2,2′-bipyridine, dcbpy=4,4′-dicarboxyl-2,2′-bipyridine, bpy=2,2′-bipyridine), was investigated using steady-state and time-resolved absorption and emission spectra, and photoinduced inter-molecular electron transfer between [Ru(bpy) 2(dmbpy)](PF 6) 2 ( 1) (dmbpy=4,4′-dimethyl-2,2′-bipyridine) and N, N-dimethylaniline was also studied for comparison. While inter-molecular reductive quenching of 1’s emission by aniline was less efficient, nearly half emission was quenched intra-molecularly in 2. Upon photoinduced electron injection onto the conduction band of TiO 2 from 3 or 4 anchored on the TiO 2 surface, intra-molecular electron transfer from aniline moiety to Ru(III) orbital occurred rapidly with rate constants of 3.4×10 7 and 2.6×10 7 s −1, respectively, restricting the interfacial recombination of injected electrons with Ru(III) and as a result improving the photoelectrochemical behavior of 3 or 4 when used in dye-sensitized nanocrystalline semiconductor solar cells.

Photochemistry of a Dumbbell-Shaped Multicomponent System Hosted Inside the Mesopores of Al/MCM-41 Aluminosilicate. Generation of Long-Lived Viologen Radicals

A dumbbell-shaped compound, 26+, comprising a Ru(II) polypyridine complex, a p-terphenyl, a 4,4‘-bipyridinium unit, a 3,3‘-dimethyl-4,4‘-bipyridinium unit, and a tetraarylmethane unit, has been enclosed in the channels (3.2 nm diameter) of an Al/MCM-41 aluminosilicate. Evidence for the internal location of 26+ in the Al/MCM-41 host was obtained by mapping the C/Si and N/Si atomic ratios as a function of the depth of penetration into the interior of the aluminosilicate particles. The photoluminescence of the Ru(II) polypyridine unit, when 26+ is enclosed within Al/MCM-41, is red-shifted, and the excited state is considerably shorter-lived compared with the behavior of 26+ in acetonitrile solution. Laser flash photolysis experiments on 26+ enclosed in the aluminosilicate matrix yield different results depending on the excitation wavelength. Selective excitation (532 nm light) of the Ru polypyridine component formed, together with oxidized Ru complex moieties, long-lived (millisecond time scale) radical cati...

Mono-, di-, and tetranuclear ruthenium(II) complexes containing 3-(pyridin-2-yl)-as-triazino[5,6-f]1,10-phenanthroline: synthesis, characterization, and electrochemical and photophysical properties.

Mono-, di-, and tetranuclear Ru(II) polypyridine complexes based on the bridging ligand pdtp, where pdtp is 3-(pyridin-2-yl)-as-triazino[5,6-f]1,10-phenanthroline, have been synthesized and characterizated. This asymmetric bridging ligand is composed of two nonequivalent coordinating sites: one involves the phenanthroline moiety, and the other one involves the pyridyltriazine moiety. Electrochemical data show that the first redox process in these complexes is pdtp based and the metal-metal interaction in di- and tetranuclear complexes is very weak. The two oxidations (+1.41 and +1.56 V vs SCE) observed in dinuclear complex 2 are mainly ascribed to the different coordination environments of two metal centers. Absorption spectra are essentially the sum of the spectra of the component monometallic species. The emission spectra are measured both at room temperature and at 80 K in a 4:1 (v/v) EtOH/MeOH matrix. The complexes all display luminescence properties which are close to that featured by the parent [Ru(phen)(3)](2+) species. It is also noted that center-to-periphery energy transfer occurs in the dendritic tetranuclear complex 3.

Electronic properties and interface characterization of phthalocyanine and Ru-polypyridine dyes on TiO 2 surface

Electronic structures, energy levels alignment and electronic interactions of a series of phthalocyanine and Ru-polypyridine dyes at the interfaces of dyes/TiO 2 films have been studied by photoelectron spectroscopy. The shifts of carboxylic C 1s core level binding energies of carboxylated dye complexes at different adsorption states indicate that the dyes are mainly adsorbed on the nanoporous TiO 2 surface via carboxylic groups. The relative positions of the highest occupied molecular orbitals/the lowest unoccupied molecular orbitals (HOMO/LUMO) of these phthalocyanine and Ru-polypyridine dyes with respective to the conduction band (CB) of TiO 2 were determined from a combination of X-ray and ultraviolet photoemission (XPS and UPS) measurements and further compared with their corresponding electrochemical oxidation potentials. Both measurements support the general picture of Ru-polypyridine complexes that their HOMO has predominately core metal Ru 4d(t 2g) character while for phthalocyanine dyes the HOMO energy levels are more related to their chromophores.

Ruthenium(II) dendrimers containing carbazole-based chromophores as branches.

Three new luminescent and redox-active Ru(II) complexes containing novel dendritic polypyridine ligands have been synthesized, and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox behavior have been investigated. The dendritic ligands are made of 1,10-phenanthroline coordinating subunits and of carbazole groups as branching sites. The first and second generation species of this novel class of dendritic ligands (L1 and L2, respectively; see Figure 1 for their structural formulas) have been prepared and employed. The metal dendrimers investigated are [Ru(bpy)(2)(L1)](2+) (1; bpy = 2,2'-bipyridine), [Ru(bpy)(2)(L2)](2+) (2), and [Ru(L1)(3)](2+) (3; see Figure 2). For the sake of completeness and comparison purposes, also the absorption spectra, redox behavior, and luminescence properties of L1 and L2 have been studied, together with the properties of 3,6-di(tert-butyl)carbazole (L0) and [Ru(bpy)(2)(phen)](2+) (4, phen = 1,10-phenanthroline). The absorption spectra of the free dendritic ligands show features which can be assigned to the various subunits (i.e., carbazole and phenanthroline groups) and additional bands at lower energies (at lambda > 300 nm) which are assigned to carbazole-to-phenanthroline charge-transfer (CT) transitions. These latter bands are significantly red-shifted upon acid and/or zinc acetate addition. Both L1 and L2 exhibit relatively intense luminescence at room temperature in fluid solution (lifetimes in the nanosecond time scale, quantum yields of the order of 10(-2)-10(-1)) and at 77 K in rigid matrix (lifetimes in the millisecond time scale). Such a luminescence is assigned to CT states at room temperature and to phenanthroline-centered pi-pi triplet levels at 77 K. The room-temperature luminescence of L1 and L2 is totally quenched by acid or zinc acetate. The metal dendrimers exhibit the typical absorption and luminescence properties of Ru(II) polypyridine complexes. In particular, metal-to-ligand charge-transfer (MLCT) bands dominate the visible absorption spectra, and formally triplet MLCT levels govern the excited-state properties. Excitation spectroscopy evidences that all the light absorbed by the dendritic branches is transferred with unitary efficiency to the luminescent MLCT states in 1-3, showing that the new metal dendrimers can be regarded as efficient light-harvesting antenna systems. All the free ligands and metal dendrimers exhibit a rich redox behavior (except L2 and 3, whose redox behavior was not investigated because of solubility reasons), with clearly attributable reversible carbazole- and metal-centered oxidation and polypyridine-centered reduction processes. The electronic interaction between the carbazole redox-active sites of the dendritic ligands is affected by Ru(II) coordination.

New dinuclear Ru(II) complexes containing free chelating polypyridine sites within the bridging ligands: absorption spectra, luminescence properties, redox behavior and sensing properties.

A series of dinuclear Ru(II) polypyridine complexes have been prepared and their absorption spectra and luminescence properties (both at room temperature in acetonitrile fluid solution and at 77 K in butyronitrile rigid matrix) have been investigated. The species studied are [(bpy)2Ru(L1)Ru(bpy)2]4+ (1; bpy = 2,2'-bipyridine). [(tpy)Ru(Ln)Ru(tpy)]4+ (2, Ln = L2; 3, Ln = L3; 4, Ln = L4; tpy = 2,2':6',2"-terpyridine; for L1-L4 bridging ligands, see Fig. 1). All the 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. The compounds also exhibit relatively intense emissions, originating from triplet MLCT levels, both at 77 K and at room temperature. All the new compounds contain a free chelating bipyridine site within their bridging ligand structure, and this confers to the new species interesting properties as far as the effect of perturbation (e.g., addition of acid or zinc salts) on the absorption and luminescence properties is concerned. Indeed, the luminescence intensity of each species is strongly affected by the presence of protons or cations. In particular, upon acid or zinc salts addition the luminescence intensity of 1 decreases, while the luminescence intensity of 2-4 increases. This different behaviour is related to the different dominating pathways for MLCT excited-state decay in Ru(II) chromophores containing tridentate or bidentate polypyridine ligands The redox behavior of 1 and 2 has also been investigated in acetonitrile solution in the absence and presence of zinc salts. It has been found that the electronic interaction between the peripheral chromophores is enhanced by zinc coordination.