Synthesis, Characterization, Photophysical, and Anion-Binding Studies of Luminescent Heteroleptic Bis-Tridentate Ruthenium(II) Complexes Based on 2,6-Bis(Benzimidazole-2-yl)Pyridine and 4′-Substituted 2,2′:6′,2′′ Terpyridine Derivatives

Control of Photoisomerization Kinetics via Multistage Switching in Bimetallic Ru(II)-Terpyridine Complexes

In this study, we carried out detailed experimental and theoretical investigation on photophysical, electrochemical, and photoisomerization behaviors of a new array of luminescent binuclear Ru(II) complexes derived from a phenylene-vinylene-substituted terpyridyl ligand possessing RT lifetimes within 60.3-410.5 ns. The complexes experienced trans-to-cis isomerization in MeCN on irradiation with visible light, accompanied by significant changes in their absorption and emission spectral profiles. The reverse cis-to-trans process is also possible with the use of ultraviolet (UV) light. On conversion from trans to cis isomers, the emission intensity increases substantially, while for the reverse process, luminescence quenching occurs. Thus, "off-on" and "on-off" emission switching is facilitated upon treatment with visible and UV light alternatively. By the use of chemical oxidants (ceric ammonium nitrate and potassium permanganate) and reductants (metallic sodium) as well as light of appropriate wavelengths, multistate switching phenomena involving reversible oxidation-reduction and trans-cis isomerization have been achieved. Interestingly, the rate of this multistate photoswitching process becomes much faster compared to only two-state trans-cis isomerization of these complexes. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations are also performed to obtain a clear picture of the electronic environment of the complexes and also for the appropriate assignment of absorption and emission spectral bands.

A photo-degradable BODIPY-modified Ru(II) photosensitizer for safe and efficient PDT under both normoxic and hypoxic conditions

Photodynamic therapy (PDT) is promising for cancer treatment but still suffers from some limitations. For instance, PDT based on 1O2 generation (in a type-II mechanism) is heavily dependent on high oxygen concentrations and will be significantly depressed in hypoxic tumors. In addition, the residual photosensitizers after PDT treatment may cause severe side-effects under light irradiation. To solve these problems, herein a BODIPY (boron dipyrromethene)-modified Ru(II) complex [Ru(dip)2(tpy-BODIPY)]2+ (complex 1, dip = 4,7-diphenyl-1,10-phenanthroline, tpy = 2,2':6',2''-terpyridine) was designed and synthesized. Complex 1 exhibited both high singlet oxygen quantum yield (Φ = 0.7 in CH3CN) and excellent superoxide radical (O2˙-) generation, and thus demonstrated efficient PDT activity under both normoxic and hypoxic conditions. Moreover, complex 1 is photo-degradable in water, and greatly loses its ROS generation ability after PDT treatment. These novel properties of complex 1 make it promising for efficient PDT under both normoxic and hypoxic conditions with reduced side-effects.

Design of molecular sensors and switches based on luminescent ruthenium-terpyridine complexes bearing active methylene and triphenylphosphonium motifs as anion recognition sites: experimental and DFT/TD-DFT investigation

Synthesis, characterization and thorough investigation of the photophysical and electrochemical properties of a new category of emissive homo- and heteroleptic Ru(II)-complexes derived from the [4'-(p-triphenylphosphonium methyl phenyl)-2,2':6',2''-terpyridine]bromide (tpy-PhCH2PPh3Br) ligand have been executed in this work. Incorporation of the PhCH2PPh3+Br- group at the terpyridine motif appropriately adjusts the triplet metal-to-ligand charge transfer (3MLCT) and metal-centered (3MC) excited states so that the complexes luminesce at room temperature (RT) having lifetimes within the range of 6.82-9.63 ns. The RT emission characteristics of the complexes get further enhanced via aggregation phenomena through the use of different solvent/non-solvent mixtures (DMSO/H2O and DMSO/PhCH3 mixtures). Temperature dependent emission spectral measurements indicate that the emission intensity, quantum yield and lifetime increase upon dropping down the temperature, thereby designated as the on-state, while the increase of temperature causes a reduction of the said properties, indicating the off-state and the process is fully reversible. Taking advantage of the active methylene group coupled with a phosphonium motif, anion sensing characteristics of the complexes are investigated systematically in DMSO through the use of various optical channels and spectroscopic tools. The complexes are very much sensitive to fluoride and to a lesser extent acetate and dihydrogen phosphate among the studied anions. In essence, the complexes function as sensors for temperature and fluoride ion. Computational investigations were also executed via density functional theory (DFT) and time-dependent (TD)-DFT to obtain a clear understanding of the electronic structures of the metalloreceptors, appropriate assignment of the spectral bands and their mode of interaction with selected anions.

Influences of Both N,N,N- and N,N,C-Coordination Modes of Tolyl-terpyridine on the Photophysical Properties of Cyclometalated Ru(II) Complexes: Combined Experimental and Theoretical Investigations on Acid/Base-Dependent Reversible Cyclometalation

With the goal of developing a new strategy for the synthesis of luminescent Ru(II) complexes, we have prepared herein a new set of bis-tridentate complexes of the type [(py-bpy-Ph-X)Ru(tpy-PhCH3)]ClO4 (X = -CH3, -CH2Br, and -CHO) incorporating both non-cyclometalated and cyclometalated coordination motifs of two isomeric forms of methylphenyl-terpyridine (tpy-PhCH3). Thorough characterization of the synthesized complexes is carried out using standard analytical tools and single crystal X-ray diffraction. Detailed investigations on their photophysical and electrochemical behaviors are carried out in MeCN. The presence of a carbanionic center in the cyclometalating unit increases the absorption spectral window of the complexes into a longer-wavelength region. The complexes also exhibit room-temperature luminescence in the NIR domain with enhanced excited-state lifetimes (up to 20.1 ns) compared to their non-cyclometalated counterpart, [Ru(tpy-PhCH3)2]2+. In the presence of acid, the non-coordinated nitrogen atom in the secondary coordination sphere of the complexes allows fine-tuning of the absorption and emission spectral properties. Excess acid induces de-coordination of the Ru-C bond, which is signaled by a remarkable alteration of their spectral profiles. Cleavage of the Ru-C bond is also possible upon treating the acidified solution of the complexes with visible light. Restoration of the Ru-C bond is again feasible upon treating the solution with base at an elevated temperature (∼70 °C). In essence, "on-off" and "off-on" switching of emission is facilitated upon alternating treatment of the Ru(II) complexes with acid, base, and temperature. DFT and TD-DFT calculations are also performed for assignments of the spectral bands as well as to understand structural changes associated with the switching behaviors of the complexes.

A New Unnatural Amino Acid Derived from the Modification of 4′-(p-tolyl)-2,2′:6′,2″-terpyridine and Its Mixed-Ligand Complexes with Ruthenium: Synthesis, Characterization, and Photophysical Properties

The modification of the methyl group of 4′-(p-tolyl)-2,2′:6′,2″-terpyridine produced the novel unnatural amino acid 3-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)-2-aminopropanoic acid (phet). Mononuclear heteroleptic ruthenium complexes of the general formulae [Ru(L1)(L2)](PF6)2 (L1 = 2-acetylamino-2-(4-[2,2′:6′,2″]terpyridine-4′-yl-benzyl)-malonic acid diethyl ester, (phem), 3-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)-2-aminopropanoic acid, (phet), and L2 = 2,2′:6′,2″-terpyridine (tpy), 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy), 4′-(p-tolyl)-2,2′:6′,2″-terpyridine (mptpy)), as well as the homoleptic [Ru(phem)2](PF6)2 and [Ru(phet)2](PF6)2, were synthesized and characterized by means of NMR spectroscopic techniques, elemental analysis, and high-resolution mass spectrometry. The photophysical properties of the synthesized complexes were also studied.

Neural network and decision tree-based machine learning tools to analyse the anion-responsive behaviours of emissive Ru(ii)–terpyridine complexes

Artificial neural network, adaptive neuro-fuzzy inference and decision tree regression are implemented to analyse the anion-responsive behaviours of emissive Ru(ii)–terpyridine complexes.

Bichromophoric ruthenium(II) bis-terpyridine-BODIPY based photosensitizers for cellular imaging and photodynamic therapy

Two multichromophoric homoleptic ruthenium(II) complexes [Ru(tpy-BODIPY)₂]Cl₂ (complexes 1 and 2, tpy = 4-phenyl-2,2:6,2-terpyridine, BODIPY = boron-dipyrromethene) were prepared, characterized and their phototherapeutic activity and bioimaging properties were studied. The complexes having structural similarity differ only by a phenylethynyl linker, and its overall influence on their physicochemical and photobiological behavior was evaluated. The terpyridine-BODIPY ligand L¹ was structurally characterized by X-ray crystallography. The complexes showed intense absorption near 500 nm (ε: ∼1.5 × 10⁵ M^-1 cm^-1 in DMSO), have a high singlet oxygen quantum yield (Φ_Δ: ∼0.6 in DMSO), and displayed low photobleaching thus making them suitable for PDT applications. The complexes showed high DNA binding affinity and induced DNA damage on light activation via multiple types of ROS production. Confocal laser scanning microscopy experiments revealed their incorporation in the cancer cells and complex 1 predominantly accumulated in lysosomes. The complexes displayed a significant PDT effect in cancerous cells with visible light activation with a high photocytotoxicity index (PI) value in HeLa cells. Both type-I and type-II photosensitization processes were involved in the PDT effect. The photodynamic action of complex 2 initiated cellular apoptosis. Finally, their diagnostic potential was evaluated against clinically relevant 3D multicellular tumor spheroids (MCTs).

Neuro-Fuzzification Architecture for Modeling of Electrochemical Ion-Sensing Data of Imidazole-Dicarboxylate-Based Ru(II)-Bipyridine Complex

Anion- and pH-sensing behaviors of an imidazole-dicarboxylate-based Ru(II)-bipyridine complex possessing a number of dissociable protons in its secondary coordination sphere are employed here for the creation of multiple Boolean and fuzzy logic systems. The absorption, emission, and electrochemical behaviors of the metalloreceptor were significantly modulated upon the influence of basic anions (such as F^-, AcO^-, and H₂PO₄^-) as well as by altering the pH of the solution. Interestingly, the deprotonation of the metalloreceptor by selected anions or by alkaline pH, followed by its restoration to its original form by acid or acidic pH is reversible and could be repeated many times. The metalloreceptor is capable to demonstrate several advanced Boolean functions, namely, three-input OR gate, set-reset flip-flop logic, and traffic signal, by employing its electrochemical responses through proper use of different inputs. Administering exhaustive sensing experiments by changing the analyte concentration within a wide range is usually tedious as well as exorbitantly costly. To get rid of these difficulties, we employed here several soft computing approaches such as artificial neural networks (ANN), fuzzy logic systems (FLS), or adaptive neuro-fuzzy inference system (ANFIS) to foresee the experimental sensing data and to appropriately model the protonation-deprotonation behaviors of the metalloreceptor. Reasonably good correlation between the experimental and model output data is also reflected in their tested root-mean-square error values (0.115961 and 0.118894 for the ANFIS model).

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors

Luminescence chemosensors are one of the most useful tools for the determination and imaging of small biomolecules and ions in situ in real time. Based on the unique photo-physical/-chemical properties of ruthenium(II) (Ru(II)) complexes, the development of Ru(II) complex-based chemosensors has attracted increasing attention in recent years, and thus many Ru(II) complexes have been designed and synthesized for the detection of ions and small biomolecules in biological and environmental samples. In this work, we summarize the research advances in the development of Ru(II) complex-based chemosensors for the determination of ions and small biomolecules, including anions, metal ions, reactive biomolecules and amino acids, with a particular focus on binding/reaction-based chemosensors for the investigation of intracellular analytes’ evolution through luminescence analysis and imaging. The advances, challenges and future research directions in the development of Ru(II) complex-based chemosensors are also discussed.

BODIPY-Ruthenium(II) Bis-Terpyridine Complexes for Cellular Imaging and Type-I/-II Photodynamic Therapy

A series of multichromophoric ruthenium(II) complexes with the formulation [Ru(tpy-BODIPY)(tpy-R)]Cl2 (1-4), having a heteroleptic Ru(II)-bis-tpy (tpy = 4'-phenyl-2,2':6',2″-terpyridine) moiety covalently linked to a boron-dipyrromethene (BODIPY) pendant, have been prepared and characterized and their application as a phototherapeutic and photodetection agent in cancer therapy has been explored. Ligand L1 with a terpyridine-BODIPY moiety and complex 1 as its PF6 salt (1a) have been structurally characterized by a single-crystal X-ray diffraction study. Complex 1a has a distorted-octahedral RuN6 core with a Ru(II)-bis-terpyridine unit that is covalently linked to one photoactive BODIPY unit. The complexes exhibit strong absorbance near 502 nm (ε ≈ (3.7-7.8) × 104 M-1 cm-1) and high singlet oxygen sensitization ability, giving singlet oxygen quantum yield (ΦΔ) values ranging from 0.57 to 0.75 in DMSO. An emission-based study using complex 4 and Singlet Oxygen Sensor Green (SOSG) displays the formation of singlet oxygen inside the cells and also in the buffer medium upon light irradiation. DNA (pUC19) photocleavage experiments using ROS scavengers/stabilizers reveal photoinduced generation of singlet oxygen by a type-II process and of the superoxide anion radical by a type-I process. Complex 4 having a pendant biotin moiety as a cancer cell targeting group shows high photocytotoxicity with a remarkable phototherapeutic index (PI) value of >1400 in HeLa cancer cells with a low light dose activation (400-700 nm, 2.2 J cm-2). The complexes display reduced activity in noncancerous HPL1D cells. The emission property of the complexes is used for cellular imaging, thus making them suitable as next-generation theranostic PDT agents.

Exploitation of the Second Coordination Sphere to Promote Significant Increase of Room-Temperature Luminescence Lifetime and Anion Sensing in Ruthenium-Terpyridine Complexes

This paper deals with the synthesis, characterization, and photophysical behaviors of three Ru(II)-terpyridine complexes derived from a terpyridyl-imidazole ligand (tpy-HImzPh₃Me₂), wherein a terpyridine moiety has been coupled with a dimethylbenzil unit through a phenylimidazole spacer. The three complexes display strong emission at RT having excited-state lifetimes in the range of 2.3-43.7 ns, depending upon the co-ligand present and the solvents used. Temperature-dependent emission spectral measurements have demonstrated that the energy separation between emitting metal-to-ligand charge transfer state and non-emitting metal-centered state is increased relative to that of [Ru(tpy)₂]²⁺. In contrast to our previously studied Ru(II) complexes containing similar terpyridyl-imidazole motif but differing by peripheral methyl groups, significant enhancement of RT emission intensity and quantum yield and remarkable increase of emission lifetime occur for the present complexes upon protonation of the imidazole nitrogen(s) with perchloric acid. Additionally, by exploiting imidazole NH motif(s), we have examined their anion recognition behaviors in organic and aqueous media. Interestingly, the complexes are capable of visually recognizing cyanide ions in aqueous medium up to the concentration limit of 10^-8 M. Computational studies involving density functional theory (DFT) and time-dependent DFT methods have been carried out to obtain insights into their electronic structures and to help with the assignment of absorption and emission bands.

pH-Responsive colorimetric, emission and redox switches based on Ru(ii)-terpyridine complexes

We have undertaken a thorough investigation on pH-responsive optical and redox switching behaviors of our recently reported trans form of bis-tridentate Ru(ii) luminophores, [(H₂pbbzim)Ru(tpy-pvp-X)]²⁺ where X = H, Me, Cl, NO₂, and Ph. The complexes possess two benzimidazole protons in their second coordination sphere, which became acidic upon coordinating influence of Ru²⁺ and could be successively deprotonated with the increase of pH. The effect of pH on photophysical and electrochemical behaviours of the complexes was thoroughly studied. Substantial quenching of emission together with the red-shift of both absorption (color change) and emission bands is noticed for all complexes upon dissociation of NH protons. Absorption vs. pH data were employed for determination of ground-state pK_a values, while excited-state pK_a (pK_a*) values were estimated by employing the Förster cycle based equation. The electronic nature of X induces a small but finite effect on the pK_a values and a linear correlation is found by plotting pK_avs. Hammett σ_p parameters of X. Proton-coupled electrochemical behaviours were investigated within the pH range of 1-10. From the E_1/2vs. pH plot, acid dissociation constants in different protonation states of the complexes were estimated in both Ru²⁺ and Ru³⁺ states. Compared with their protonated forms which exhibit reversible oxidation within 0.91-0.95 V, the oxidation potential of the doubly deprotonated forms shifted remarkably to the cathodic region (0.61-0.66 V). In essence, the present complexes act as potential pH-responsive colorimetric, emission and redox switches.

Fluorescence turn-on chemodosimetric sensing of cyanide by cyanovinylterpyridine modified phthalonitrile and subphthalocyanine

Terpyridine-attached phthalonitrile (Pn-TP) linked by cyanovinyl bond has been synthesized and employed for the preparation of subphthalocyanine (SubPc-TP) bearing conjugated terpyridine moieties. Both Pn-TP and SubPc-TP exhibited highly selective fluorescence turn-on in the presence of cyanide anions (CN^-) based on chemodosimetric sensing mechanism. The conjugation of the Pn-TP molecule was interrupted by the addition of CN^- at the cyanovinyl bond, showing the ratiometric fluorescence turn-on behavior. This sensing mechanism was further supported by density functional theory calculation and nuclear magnetic resonance titration studies. Optical and photophysical responses of SubPc-TP towards CN^- were also investigated, in which similar fluorescence enhancement was observed due to the addition of CN^- at the reactive boron trimer. The detection limit was estimated to be 94 nM, much below the World Health Organization-allowed level (1.9 μM) of CN^- in water.

Anion and pH dependent molecular motion by a halogen bonding [2]rotaxane

A bistable [2]rotaxane containing a halogen bonding benzimidazole-iodotriazole station directly conjugated to a naphthalimide station axle component is demonstrated to undergo macrocycle shuttling translocation only upon both protonation and chloride anion recognition. A naked-eye detectable colour response results from the co-conformational change of the host structure.

Synthesis, Photophysics, and Switchable Luminescence Properties of a New Class of Ruthenium(II)-Terpyridine Complexes Containing Photoisomerizable Styrylbenzene Units

We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru(II) containing styrylbenzene moieties to improve room-temperature luminescence properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0-158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σ_p parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans-trans to trans-cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans-cis to trans-trans forms was also achieved on interacting with visible light. Change from trans-trans to the corresponding trans-cis form leads to emission quenching, whereas trans-cis to the corresponding trans-trans form leads to restoration of emission. In essence, "on-off" and "off-on" photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands.

Semiempirical configuration interaction calculations for ru-centered dyes

Computational investigation of the photochemical properties of transition-metal-centered dyes typically involves optimization of the molecular structure followed by calculation of the UV/visible spectrum. At present, these steps are usually carried out using density functional theory (DFT) and time-dependent DFT calculations. Recently, we demonstrated that semiempirical methods with appropriate parameterization could yield geometries that were in very good agreement with DFT calculations, allowing large sets of molecules to be screened quickly and efficiently. In this article, we modify a configuration interaction (CI) method based on a semiempirical PM6 Hamiltonian to determine the UV/visible absorption spectra of Ru-centered complexes. Our modification to the CI method is based on a scaling of the two-center, two-electron Coulomb integrals. This modified, PM6-based method shows a significantly better match to the experimental absorption spectra versus the default configuration interaction method (in MOPAC) on a training set of 13 molecules. In particular, the modified PM6 method blue-shifts the location of the metal-to-ligand charge-transfer (MLCT) peaks, in better agreement with experimental and DFT-based computational results, correcting a significant deficiency of the unmodified method. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Synthesis, Structural Characterization, and Luminescence Switching of Diarylethene-Conjugated Ru(II)-Terpyridine Complexes by trans-cis Photoisomerization: Experimental and DFT/TD-DFT Investigation

We synthesized and thoroughly characterized a new family of diarylethene-conjugated mononuclear Ru(II)-terpyridine complexes and investigated in detail their photophysical, electrochemical, and spectroelectrochemical behaviors. Interestingly, the compounds show moderately strong room-temperature luminescence predominantly from their ³MLCT state with luminescence lifetime varying between 8.43 and 22.82 ns. Because of the presence of diarylethene unit, all the monometallic complexes underwent trans-to-cis photoisomerization upon interaction with UV light with substantial changes in their absorption and luminescence spectra. Reverting back from the cis to the trans form is also made possible upon treatment with visible light or by heat. Trans-to-cis isomerization leads to almost complete quenching of luminescence, while backward cis-to-trans isomerization gives rise to restoration of the original luminescence for all the complexes. Thus, "on-off" and "off-on" emission switching was made possible upon successive interaction of the complexes with UV and visible light. Computational investigation involving density functional theory (DFT) and time-dependent DFT methods was done for proper assignment of the experimental absorption and emission spectral bands in the complexes. Finally, experimentally observed trend on the absorption and emission spectral behaviors of the complexes upon photoisomerization was also compared with the calculated results.

pH-Switchable "Off-On-Off" Near-Infrared Luminescence Based on a Dinuclear Ruthenium(II) Complex

The pH-switchable room-temperature near-infrared (NIR) phosphorescence emission based on ruthenium(II) polypyridyl complexes has been very rarely reported, even though it is very desirable for applications in sensing, switching, and logic molecular devices and bioimaging. Here we report a novel dinuclear ruthenium(II) complex in an aerated acetonitrile solution featuring a bright NIR emission centered at 760 nm with an absolute quantum yield of 1.03%, a large Stokes shift of 254 nm, and a long emission lifetime of 108.3 ± 0.4 ns. The complex in a Britton-Roberson buffer also exhibited pH-induced "off-on-off" NIR luminescent switches with a maximum intensity enhancement factor of 41 and one of the switching events occurring near the physiological pH range.

A ruthenium(iii) complex derived from N,N′-bis(salicylidene)ethylenediamine as a chemosensor for the selective recognition of acetate and its interaction with cells for bio-imaging: experimental and theoretical studies

A ruthenium(iii) complex ofN,N′-bis(salicylidene)ethylenediamine (L¹) was used as chemosensor for the recognition of acetate in cells for bio-imaging.

Predicting Structures of Ru-Centered Dyes: A Computational Screening Tool

Dye-sensitized solar cells (DSCs) represent a means for harvesting solar energy to produce electrical power. Though a number of light harvesting dyes are in use, the search continues for more efficient and effective compounds to make commercially viable DSCs a reality. Computational methods have been increasingly applied to understand the dyes currently in use and to aid in the search for improved light harvesting compounds. Semiempirical quantum chemistry methods have a well-deserved reputation for giving good quality results in a very short amount of computer time. The most recent semiempirical models such as PM6 and PM7 are parametrized for a wide variety of molecule types, including organometallic complexes similar to DSC chromophores. In this article, the performance of PM6 is tested against a set of 20 molecules whose geometries were optimized using a density functional theory (DFT) method. It is found that PM6 gives geometries that are in good agreement with the optimized DFT structures. In order to reduce the differences between geometries optimized using PM6 and geometries optimized using DFT, the PM6 basis set parameters have been optimized for a subset of the molecules. It is found that it is sufficient to optimize the basis set for Ru alone to improve the agreement between the PM6 results and the DFT results. When this optimized Ru basis set is used, the mean unsigned error in Ru-ligand bond lengths is reduced from 0.043 to 0.017 Å in the set of 20 test molecules. Though the magnitude of these differences is small, the effect on the calculated UV/vis spectra is significant. These results clearly demonstrate the value of using PM6 to screen DSC chromophores as well as the value of optimizing PM6 basis set parameters for a specific set of molecules.

Substituent directed selectivity in anion recognition by a new class of simple osmium-pyrazole derived receptors

The present article deals with the structurally, spectroscopically and electrochemically characterised osmium-bipyridyl derived complexes [(bpy)2Os(II)(HL1)Cl]ClO4 [1]ClO4 and [(bpy)2Os(II)(HL2)Cl]ClO4 [2]ClO4 incorporating neutral and monodentate pyrazole derivatives (HL) with one free NH function (bpy = 2,2'-bipyridine, HL1 = pyrazole, HL2 = 3,5-dimethylpyrazole). The crystal structures of [1]ClO4 and [2]ClO4 reveal intramolecular hydrogen bonding interactions between the free NH proton of HL and the equatorially placed Cl(-) ligand (N-HCl) with donor-acceptor distances of 3.114(7) Å and 3.153(6) Å as well as intermolecular hydrogen bonding interactions between the NH proton and one of the oxygen atoms of ClO4(-) (N-HO) with donor-acceptor distances of 2.870(10) Å and 3.024(8) Å, respectively. The effect of hydrogen bonding interactions has translated into the less acidic nature of the NH proton of the coordinated HL with estimated pKa > 12. 1(+) and 2(+) exhibit reversible Os(II)/(III) and irreversible Os(III)/(IV) processes in CH3CN within ± 2.0 V versus SCE. The effect of 3,5-dimethyl substituted HL2 on 2(+) has been reflected in the appreciable lowering (40 mV) of the Os(II/III) potential, along with the further decrease in the acidity of the NH proton (pKa > 13.0) with regard to HL1 coordinated 1(+) (pKa: ∼ 12.3). The electronic spectral features of Os(ii) (1(+)/2(+)) and electrochemically generated Os(III) (1(2+)/2(2+)) derived complexes have been analysed by TD-DFT calculations. The efficacy of the 1(+) and 2(+) encompassing free NH proton towards the anion recognition process has been evaluated by different experimental investigations using a wide variety of anions. It however establishes that receptor 1(+) can recognise both F(-) and OAc(-) in acetonitrile solution, while 2(+) is exclusively selective for the F(-) ion.

Demonstration of intramolecular energy transfer in asymmetric bimetallic ruthenium(ii) complexes

Asymmetric bimetallic Ru(ii) complexes exhibit photo-induced intramolecular energy transfer with rate constant values on the order of 10⁷ s⁻¹.

Molecular ruthenium water oxidation catalysts carrying non-innocent ligands: mechanistic insight through structure–activity relationships and quantum chemical calculations

Herein is highlighted how structure–activity relationships can be used to provide mechanistic insight into H₂O oxidation catalysis.

Ruthenium bistridentate complexes with non-symmetrical hexahydro-pyrimidopyrimidine ligands: a structural and theoretical investigation of their optical and electrochemical properties

The optical and electronic properties of six Ru complexes with non-symmetrical tridentate ligands have been investigated and, as corroborated by electrochemical data, the presence of the hpp ligand strongly affects the oxidation potential of the metal ion.

Potential anion sensing properties by a redox and substitution series of [Ru(bpy)3−n(Hdpa)n]2+, n = 1–3; Hdpa = 2,2′-dipyridylamine: selective recognition and stoichiometric binding with cyanide and fluoride ions

Efficient anion sensors [Ru(bpy)_3−n(Hdpa)_n]²⁺, n = 1–3 have been developed for selective recognition of cyanide and fluoride ions with remarkable stoichiometric binding.

Synthesis, electrochemical and spectroscopic properties of ruthenium(ii) complexes containing 2,6-di(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)aryl ligands

Five mono and dinuclear ruthenium complexes containing various symmetrical 2,6-di(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)aryl ligands were synthetized and their physical–chemical properties were studied.

Theoretical and experimental studies of phenol oxidation by ruthenium complex with N,N,N-tris(benzimidazol-2yl-methyl)amine

The ruthenium complex with (N,N,N-tris(benzimidazol-2yl-methyl)amine, L(1)) was prepared, and characterized. Fukui data were used to localize the reactive sites on the ligand. The structural and electronic properties of the complex were analyzed by DFT in different oxidation states in order to evaluate its oxidant properties for phenol oxidation. The results show that the hard Ru(IV) cation bonds preferentially with a hard base (Namine = amine nitrogen, or axial chloride ion), and soft Ru(II) with a soft base (Nbzim = benzimidazole nitrogen or axial triphenyl phosphine). Furthermore, the Jahn-Teller effect causes an elongation of the axial bond in the octahedral structure. The bonding nature and the orbital contribution to the electronic transitions of the complex were studied. The experimental UV-visible bands were interpreted by using TD-DFT studies. The complex oxidizes phenol to benzoquinone in the presence of H2O2 and the intermediate was detected by HPLC and (13)C NMR. A possible mechanism and rate law are proposed for the oxidation. The adduct formation of phenol with [Ru(O)L(1)](2+) or [Ru(OH)L(1)](+) is theoretically analyzed to show that [Ru(OH)L(1)-OPh](+) could produce the phenol radical.

Oxovanadium(IV) complexes of curcumin for cellular imaging and mitochondria targeted photocytotoxicity

Oxovanadium(IV) complexes [VO(R-tpy)(cur)](ClO4) (1, 2) of curcumin (Hcur) and terpyridine ligands (R-tpy) where R is phenyl (phtpy in 1) or p-triphenylphosphonium methylphenyl bromide (C6H4CH2PPh3Br) (TPP-phtpy in 2) were prepared and characterized and their DNA photocleavage activity, photocytotoxicity and cellular localization in cancer cells (HeLa and MCF-7) were studied. Acetylacetonate (acac) complexes [VO(R-tpy)(acac)](ClO4) of phtpy (3) and TPP-phtpy (4) were prepared and used as the control species. These complexes showed efficient cleavage of pUC19 DNA in visible light of 454 nm and near-IR light of 705 nm. Complexes 1 and 2 showed significant photocytotoxicity in visible light of 400-700 nm. FACS analysis showed sub-G1/G0 phase cell-cycle arrest in cancer cells when treated with 1 and 2 in visible light in comparison with the dark controls. Fluorescence microscopic studies revealed specific localization of the p-triphenylphosphonium complex 2 in the mitochondria of MCF-7 cancer cells whereas no such specificity was observed for complex 1.