Monometallic and bimetallic ruthenium(II) complexes derived from 4,5-bis(benzimidazol-2-yl)imidazole (H3Imbzim) and 2,2'-bipyridine as colorimetric sensors for anions: synthesis, characterization, and binding studies

Modulation of ground and excited state properties of ruthenium complexes through sequential incorporation of metal into a polypyridyl-imidazole bridging ligand

A polypyridyl-imidazole-based bridging ligand, 2-(4-(4,5-di(pyridine-2-yl)-1H-imidazole-2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (phen-H2PhImz-bpy), possessing three bidentate coordinating sites, has been designed in this work. The bridging ligand is employed to synthesize mono-, bi-, and trimetallic Ru(II) complexes in combination with terminal bipyridine units for the systematic modulation of photophysical and redox properties upon sequential incorporation of the metal unit into the bridge. All the compounds are characterized via NMR spectroscopy and electrospray ionization mass spectrometry. Absorption and both steady-state and time-resolved emission spectroscopic investigations of the ligand as well as Ru(II) complexes are thoroughly conducted in different solvents. The redox behaviors of the complexes are examined through cyclic voltammetry (CV) in acetonitrile. The focus of the investigation is centered on the systematic modulation of MLCT absorption and emission as well as the redox behavior of the complex entity upon the gradual incorporation of the Ru2+ unit into the complex backbone. The emission energy, quantum yield and lifetime are found to decrease systematically with an increase in the Ru2+ unit in the complex backbone and a linear relationship is observed in each case. A good correlation is also observed between the emission energies of complexes with their respective ΔE1/2 values (the difference between the first oxidation and first reduction potential).

A neutral rhenium-biimidazole complex for the selective recognition of fluoride ions

The neutral rhenium(I)-biimidazole complex [Re(CO)₃(biimH)(1,4-NVP)] (1) was designed and synthesized by a one-pot reaction of Re₂(CO)₁₀, 2,2'-biimidazole (biimH₂) and 4-(1-naphthylvinyl)pyridine (1,4-NVP). The structure of 1 was characterized by various spectroscopic techniques including IR, ¹H NMR, FAB-MS, and elemental analysis and further confirmed by a single-crystal X-ray diffraction analysis. The mononuclear complex 1, a relatively simple structure with an octahedral geometry, is comprised of facial-arranged carbonyl groups, one chelated biimH monoanion, and one 1,4-NVP. Complex 1 shows the lowest energy absorption band at around 357 nm and an emission band at 408 nm in THF. The luminescent characteristics of 1 combined with the hydrogen bonding ability of the partially coordinated monoionic biimidazole ligand permits the complex to selectively recognize fluoride ions (F^-) in the presence of other halides through a dramatic luminescence enhancement. The recognition mechanism of 1 can be convincingly explained in terms of H-bond formation and proton abstraction upon the addition of F^- ions by ¹H and ¹⁹F NMR titration experiments. The electronic properties of 1 were further supported by time dependent density functional theory (TDDFT) computational studies.

Unique Metal-Ligand Interplay in Directing Discrete and Polymeric Derivatives of Isomeric Azole-Carboxylate. Varying Electronic Form, C-C Coupling, and Receptor Feature

This article dealt with the ruthenium and osmium derivatives of isomeric 1H-indazole-3-carboxylic acid/2H-indazole-3-carboxylic acid (H₂L1) and 1H-benzimidazole-2-carboxylic acid (H₂L2) along with the π-acidic bpy (bpy = 2,2'-bipyridine) and pap (pap = 2-phenylazopyridine) co-ligands. It thus extended structurally authenticated monomeric ([(bpy)₂Ru^II(HL1^-)]ClO₄ [1]ClO₄, (pap)₂Ru^II(L1^2-) 2, (bpy)₂Os^II(L1^2-) 3, (pap)₂Os^II(L1^2-) 4, (bpy)₂Ru^II(L2^2-) 5, (bpy)₂Os^II(L2^2-) 8, and (pap)₂Os^II(L2^2-) 9) and dimeric ([(bpy)₂Ru^II(μ-L2^2-)Ru^II(bpy)₂](ClO₄)₂ [6](ClO₄)₂) complexes. It also described modified L2'^2- (L2'^2- = 2,2'-bisbenzimidazolate)-bridged [(pap)₂Ru^II(μ-L2'^2-)Ru^II(pap)₂](ClO₄)₂ [7](ClO₄)₂, where L2'^2- was developed selectively with the {Ru(pap)₂} metal fragment via in situ intermolecular C-C coupling of the two units of decarboxylated benzimidazolate. Moreover, chemical oxidation (Os^II to Os^III) of (bpy)₂Os^II(L1^2-) 3 (E⁰ = 0.11 V versus SCE) and (bpy)₂Os^II(L2^2-) 8 (E⁰ = 0.12 V versus SCE) by AgClO₄ yielded unprecedented Os^III-Ag^I derived polymeric {[(bpy)₂Os^III-L1^2--Ag^I(CH₃CN)](ClO₄)₂}_n {[10](ClO₄)₂}_n and dimeric [(bpy)₂Os^III-L2^2--Ag^I(CH₃CN)](ClO₄)₂ [11](ClO₄)₂ complexes as a function of trans and cis orientations of the active N2 donor with special reference to the carboxylate O2 of L^2-, respectively. Microscopic (FE-SEM, TEM-EDX, and AFM) and DLS experiments suggested a homogeneously dispersed hollow spherical shaped morphology of {[10](ClO₄)₂}_n with an average particle size of 200-400 nm as well as its non-dissociative feature in the aprotic medium. Experimental (structure, spectroscopy, and electrochemistry) and theoretical (DFT/TD-DFT) explorations revealed a redox non-innocent feature of L^2- in the present coordination situations and the selective anion sensing (X = F^-, CN^-, and OAc^-) event of [1]ClO₄ involving a free NH group at the backface of HL1^-, which proceeded via the NH···X hydrogen bonding interaction.

Development and Application of Ruthenium(II) and Iridium(III) Based Complexes for Anion Sensing

Improvements in the design of receptors for the detection and quantification of anions are desirable and ongoing in the field of anion chemistry, and remarkable progress has been made in this direction. In this regard, the development of luminescent chemosensors for sensing anions is an imperative and demanding sub-area in supramolecular chemistry. This decade, in particular, witnessed advancements in chemosensors based on ruthenium and iridium complexes for anion sensing by virtue of their modular synthesis and rich chemical and photophysical properties, such as visible excitation wavelength, high quantum efficiency, high luminescence intensity, long lifetimes of phosphorescence, and large Stokes shifts, etc. Thus, this review aims to summarize the recent advances in the development of ruthenium(II) and iridium(III)-based complexes for their application as luminescent chemosensors for anion sensing. In addition, the focus was devoted to designing aspects of polypyridyl complexes of these two transition metals with different recognition motifs, which upon interacting with different inorganic anions, produces desirable quantifiable outputs.

Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events

The article deals with the newer classes of mononuclear: [(acac)₂Ru^III(H-Iz)(Iz^-)] 1, [(acac)₂Ru^III(H-Iz)₂]ClO₄ [1]ClO₄/[1']ClO₄, and [(bpy)₂Ru^II(H-Iz)(Iz^-)]ClO₄ [2]ClO₄, mixed-valent unsymmetric dinuclear: [(acac)₂Ru^III(μ-Iz^-)₂Ru^II(bpy)₂]ClO₄ [3]ClO₄, and heterotrinuclear: [(acac)₂Ru^III(μ-Iz^-)₂M^II(μ-Iz^-)₂Ru^III(acac)₂] (M = Co:4a, Ni:4b, Cu:4c, and Zn:4d) complexes (H-Iz = indazole, Iz^- = indazolate, acac = acetylacetonate, and bpy = 2,2'-bipyridine). Structural characterization of all the aforestated complexes established their molecular identities including varying binding modes (N_a and N_b donors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz^- in the complexes. Unlike [1']ClO₄ containing two NH protons at the backface of H-Iz units, the corresponding [1]ClO₄ was found to be unstable due to the deprotonation of its positively charged quaternary nitrogen center, and this resulted in the eventual formation of the parent complex 1. A combination of experimental and density functional theory calculations indicated the redox noninnocent feature of Iz^- in the complexes along the redox chain. The absence of intervalence charge transfer transition in the near-infrared region of the (Iz^-)₂-bridged unsymmetric mixed-valent Ru^IIIRu^II state in [3]ClO₄ suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes (4a-4d) exhibited varying spin configurations due to spin-spin interactions between the terminal Ru(III) ions and the central M(II) ion. Though both [3]ClO₄ and 4a-4d displayed ligand (Iz^-/Iz^•)-based oxidation, reductions were preferentially taken place at the bpy and metal (Ru^III/Ru^II) centers, respectively. Unlike 1 or [2]ClO₄ containing one free NH proton at the backface of H-Iz, [1']ClO₄ with two H-Iz units could selectively and effectively recognize F^-, OAc^-, and CN^- among the tested anions: F^-, OAc^-, CN^-, Cl^-, Br^-, I^-, SCN^-, HSO₄^-, and Η₂PΟ₄^- in CH₃CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1']ClO₄ and 1/[2]ClO₄ could be rationalized by their pK_a values of 8.4 and 11.3/10.8, respectively.

Recognition and mechanistic investigation of anion sensing by ruthenium(II) arene complexes and bio-imaging application

In this work, four new ruthenium complexes [Ru(η⁶-p-cymene)(L1)Cl] 1, [Ru(η⁶-p-cymene)(L2)Cl] 2, [Ru(η⁶-p-cymene)(L3)Cl] 3 and [Ru(η⁶-p-cymene)(L4)Cl] 4 [HL1 = (2-cyanophenyl)glycine; HL2 = (5-chloro-2-cyanophenyl)glycine; HL3 = (2-cyano-3-fluorophenyl)glycine; HL4 = (4-cyanophenyl)glycine] were synthesized and well characterized by several spectroscopic and analytical techniques. Complexes 1 and 3 were found to be fluorescent in most of the solvents; however, 2 and 4 were found to be fluorescent mostly in EtOAc, DMF and ethanol. Amongst these four complexes, 3 has shown selective sensing against CO₃^2- and SO₄^2- anions by quenching of fluorescence. The LOD values are found to be in the sub-micromolar range. Investigations of the sensing mechanism performed by computation and NMR studies indicate a possible adduct formation between the NH group of the ligand and the anion(s) through hydrogen bond formation, which ultimately might lead to proton transfer to the bi-negative anion. The quantum yield of the complex 3 was found to decrease on addition of CO₃^2- and SO₄^2- anions from 0.46 to 0.13 and 0.12, respectively. The Job's plot indicates the binding between the probe and anion in a 1 : 1 ratio for both CO₃^2- and SO₄^2- anions. Along with that, all the complexes were found to be biocompatible when tested against several cell lines showing very high IC₅₀ values. It can also be observed that 1 is capable of penetrating within the cells and can act as a cell imaging agent showing fluorescence, and thus can be used for bio-imaging purposes.

A new multifunctional benzimidazole tagged coumarin as ratiometric fluorophore for the detection of Cd2+/F- ions and imaging in live cells

A novel multifunctional ratiometric fluorescent probe has been designed and synthesized for the selective recognition of Cd²⁺/F^- ions. The probe (3)-((2)-(1H-benzoimidazole-2-yl)-phenylimino) methyl-4-chloro-methyl-2H-chromen-2-ene (BIMC) displays excellent ratiometric responses towards Cd²⁺/F^- ions over the tested cations/anions. The lowest detection limits observed for Cd²⁺ and F^- are 1.5 × 10^-10 mol/l and 1.2 × 10^-10 mol/l respectively. Job's plot and Electro spray Ionization mass spectral (ESI-MS) studies confirms 1:1 binding stoichiometry of BIMC with Cd²⁺/F^- ions, which is further evidenced by ¹H NMR titration studies. The reversibility studies of BIMC with Cd²⁺ have been investigated using ethylenediaminetetraacetic acid (EDTA). Upon binding to Cd²⁺/F^- ions, the probe features strong ratiometric response in both UV-Visible and fluorescence spectra due to the inhibition of intramolecular charge transfer (ICT). Furthermore, the mechanism of ICT has been rationalized via solvatochromism and DFT calculations.

Long-Lived Polypyridyl Based Mononuclear Ruthenium Complexes: Synthesis, Structure, and Azo Dye Decomposition

Two mononuclear ruthenium complexes [(bpy)₂Ru^IIL₁/L₂](ClO₄)₂ ([1]²⁺/[2]²⁺) (bpy-2,2' bipyridine, L₁ = 2,3-di(pyridin-2-yl)pyrazino[2,3-f][1,10]phenanthroline) and L₂ = 2,3-di(thiophen-2-yl)pyrazino[2,3-f][1,10]phenanthroline have been synthesized. The complexes have been characterized using various analytical techniques. The complex [1]²⁺ has further been characterized by its single crystal X-ray structure suggesting ruthenium is coordinating through the N donors of phenanthroline end. Theoretical investigation suggests that the HOMOs of both complexes are composed of pyridine and pyrazine unit of ligands L₁ and L₂ whereas the LUMOs are formed by the contribution of bipyridine units. The low energy bands at ∼480 nm of the complexes can be assigned as MLCT with partial contribution from ligand transitions, whereas the rest are ligand centered. The complexes have shown Ru^II/Ru^III oxidation couples at E_1/2 at 1.26 (70 mV) V and 1.28 (62 mV) V for [1]²⁺ and [2]²⁺ vs Ag/AgCl, respectively, suggesting no significant role of distal thiophene or pyridine units of the ligands. The complexes are emissive and display solvent dependent emission properties. Both complexes have shown highest emission quantum yield and lifetime in DMSO (ϕ = 0.05 and τ_avg = 460 ns and λ_max^em at 620 nm for [1]²⁺; ϕ = 0.043 and τ_avg = 425 ns and λ_max^em at 635 nm for [2]²⁺). Further, the long luminescent lifetime of these complexes has been utilized to generate reactive oxygen species for efficient azo dye decomposition.

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.

DNA Binding Behavior, Sensor Studies, Antimicrobial, Photocleavage and In vitro Cytotoxicity of Synthesized Ru(II) Complexes with Assorted Intercalating Polypyridyl Ligands

The four novel Ru(II) polypyridyl complexes of [Ru(Hdpa)2dmbip](2+) (1), [Ru(Hdpa)2NO2-dmbip](2+) (2), [Ru(Hdpa)2debip](2+) (3) and [Ru(Hdpa)2OH-debip](2+) (4) where Hdpa = 2,2'-bipyridylamine, dmbip = 2-(4-N,N-dimethylbenzenamine)1H-imidazo[4,5-f][1,10]phenanthroline, debip = 2-(4-N,N-diethylbenzenamine)1H-imidazo[4,5-f][1,10]phenanthroline, NO2-dmbip = NO2-2-(4-N,N-dimethylbenzenamine)1H-imidazo[4,5-f][1,10]phenanthroline, OH-debip = OH-2-(4-N,N-diethylbenzenamine)1H-imidazo[4,5-f][1,10]phenanthroline were synthesized and fully characterized using elemental analysis, Mass, NMR and FT-IR. The DNA binding behavior of all synthesized complexes were investigated by using electronic absorption spectra, emission spectra, cyclic light switch on and off, sensor studies, electrochemical method and viscosity titrations. Docking studies were performed with human DNA TOP1 by using LibDock. Furthermore explore antimicrobial activity, photocleavage and in vitro cytotoxicity assay of four Ru(II) complexes.

Syntheses, crystal structures and steady state and time-resolved fluorescence properties of a PET based macrocycle and its dinuclear ZnII/CdII/HgII complexes

The present report deals with solution spectroscopic (absorption and emission) and colorimetric studies of a Robson type tetraaminodiphenol macrocyclic ligand and its ZnII2, CdII2 and HgII2 compounds.

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.

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.

Chemically-driven “molecular logic circuit” based on osmium chromophore with a resettable multiple readout

Resettable molecular processing of inputs (Cu²⁺/H₂O and F⁻/H⁺) to yield discriminating outputs and subsequent integration of logic circuits.

Pyrene-biimidazole based Ru(ii) and Os(ii) complexes as highly efficient probes for the visible and near-infrared detection of cyanide in aqueous media

Pyrenyl-biimidazole based Ru(ii) and Os(ii) complexes are used as highly efficient cyanide sensors in aqueous media.

pH luminescence switching, dihydrogen phosphate sensing, and cellular uptake of a heterobimetallic ruthenium(II)-rhenium(I) complex

A new heterobimetallic ruthenium(II)-rhenium(I) complex of [Ru(bpy)2(HL)Re(CO)3Cl](ClO4)2·6H2O (RuHLRe) {bpy = 2,2'-bipyridine and HL = 2-(4-(2,6-di(pyridin-2-yl)pyridin-4-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} was synthesised and characterised by elemental analysis, proton nuclear magnetic resonance spectroscopy, and mass spectrometry. The ground- and excited-state acid-base properties of RuHLRe were studied using UV-Vis absorption spectrophotometric and spectrofluorimetric titrations in a 100 : 1 (v/v) Britton-Robinson buffer-CH3CN solution combined with luminescence lifetime measurements. The complex exhibited two-step separate protonation-deprotonation processes in both the ground and excited states. The complex acted as pH-induced "off-on-off" luminescence switches (I(on)/I(off) = 31.0 and 14.6), with one of the switching actions being driven by pH variations over the physiological pH range (5.3-8.0). Importantly, cellular imaging and cytotoxicity experiments demonstrated that RuHLRe rapidly and selectively illuminated the membrane of HeLa cells over fixed cells and exhibited reduced cytotoxicity at the imaging concentration compared to the Re(I)-free parent Ru(II) complex. In addition, RuHLRe acted as an efficient "turn on" emission sensor for H2PO4(-) and "turn off" emission sensor for F(-) and OAc(-).

Hydrogen bonding interaction between active methylene hydrogen atoms and an anion as a binding motif for anion recognition: experimental studies and theoretical rationalization

Two new reagents, having similar spatial arrangements for hydrogen atoms of the active methylene functionalities, were synthesized and interactions of such reagents with different anionic analytes were studied using electronic spectroscopy as well as by using (1)H and (31)P NMR spectroscopic methods. Experimental studies revealed that these two reagents showed preference for binding to F(-) and OAc(-). Detailed theoretical studies along with the above-mentioned spectroscopic studies were carried out to understand the contribution of the positively charged phosphonium ion, along with methylene functionality, in achieving the observed preference of these two receptors for binding to F(-) and OAc(-). Observed differences in the binding affinities of these two reagents toward fluoride and acetate ions also reflected the role of acidity of such methylene hydrogen atoms in controlling the efficiencies of the hydrogen bonding in anion-Hmethylene interactions. Hydrogen bonding interactions at lower concentrations of these two anionic analytes and deprotonation equilibrium at higher concentration were observed with associated electronic spectral changes as well as visually detectable change in solution color, an observation that is generally common for other strong hydrogen bond donor functionalities like urea and thiourea. DFT calculations performed with the M06/6-31+G**//M05-2X/6-31G* level of theory showed that F(-) binds more strongly than OAc(-) with the reagent molecules. The deprotonation of methylene hydrogen atom of receptors with F(-) ion was observed computationally. The metal complex as reagent showed even stronger binding energies with these analytes, which corroborated the experimental results.

A new ternary copper(II) complex derived from 2-(2'-pyridyl)benzimidazole and glycylglycine: synthesis, characterization, DNA binding and cleavage, antioxidation and HSA interaction

A new ternary copper(II)-dipeptide complex [Cu(glygly)(HPB)(Cl)]⋅2H2O (glygly=glycylglycine anion, HPB=2-(2'-pyridyl)benzimidazole) has been synthesized and characterized. The DNA interaction of the complex was studied by spectroscopic methods, viscosity, and electrophoresis measurements. The antioxidant activity was also investigated using the pyrogallol autoxidation assay. Besides, the interaction of the complex with human serum albumin (HSA) in vitro was examined by multispectroscopic techniques. The complex partially intercalated to CT-DNA with a high binding constant (Kb=7.28×10(5) M(-1)), and cleaved pBR322 DNA efficiently via an oxidative mechanism in the presence of Vc, with the HO· and O2(-) as the active species, and the SOD as a promoter. Furthermore, the complex shows a considerable SOD-like activity with the IC50 value of 3.8386 μM. The complex exhibits desired binding affinity to HSA, in which hydrogen bond or vander Waals force played a major role. The alterations of HSA secondary structure induced by the complex were confirmed by UV-visible, CD, synchronous fluorescence and 3D fluorescence spectroscopy.

Binuclear ruthenium η6-arene complexes with tetradentate N,S-ligands containing the ortho-aminothiophenol motif

A series of cationic binuclear (η(6)-cymene-Ru)2 complexes with N2S2-ligands were synthesized in 64% to 85% yield by reaction of [Ru(η(6)-cymene)Cl2]2 with bis-S,S'-(ortho-aminothiophenol)-xylenes as BF4(-) and PF6(-) salts. The compounds were studied using NMR, HRMS, UV-vis and IR spectroscopy, EA and inductively coupled plasma (ICP) MS. It was determined that the hinged binuclear Ru complexes were anti and syn diastereomers obtained in 2 : 1 ratio for ortho- and meta-xylylene bridged ligands and in a 1 : 1 ratio for the para-xylylene bridged ligand. An anion effect was found for the presence of NaBF4 with the meta-xylylene bridged system yielding the targeted binuclear Ru complex and a mononuclear Ru complex. This mononuclear S,S'-coordinated η(6)-cymene Ru chloride structure lacked amine-metal coordination and was obtained in a 1 : 3 ratio of anti : syn diastereomers which were insoluble in CH2Cl2 and soluble in DMSO and DMF. X-ray crystallographic analysis was obtained for the N2S2 ligand, 1,2-bis{(2-aminophenyl)thiomethyl}benzene, showing a CS symmetry with amine groups facing outwards with a tilt of 28.95° from the ortho-aminothiophenol pendant ring. The interatomic sulfur-sulfur distance (S-S') is 4.6405 Å within the crystal structure while accommodating a potential metal bite angle from 1.0 Å to 5.9 Å when allowing rotation of the methylene phenyl bond.

Electronic structures and selective fluoride sensing features of Os(bpy)2(HL2−) and [{Os(bpy)2}2(μ-HL2−)]2+ (H3L: 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid)

The non-innocence of coordinated HL²⁻ in [(bpy)₂Os(HL²⁻)]ⁿ (1ⁿ) and (2ⁿ) and their selectivity towards F⁻ recognition were evaluated.

Development of a ruthenium(II) complex-based luminescent probe for hypochlorous acid in living cells

A novel Ru(II) complex, [Ru(bpy)2(DNPS-bpy)](PF6)2 (bpy: 2,2'-bipyridine, DNPS-bpy: 4-(2,4-dinitrophenylthio)methylene-4'-methyl-2,2'-bipyridine), has been designed and synthesized as a highly sensitive and selective luminescence probe for the recognition and detection of hypochlorous acid (HOCl) in living cells by exploiting a "signaling moiety-recognition linker-quencher" sandwich approach. The complex possesses large stokes shift (170 nm), long emission wavelength (626 nm), and low cytotoxicity. Owing to the effective photoinduced electron transfer (PET) from Ru(II) center to the electron acceptor, 2,4-dinitrophenyl (DNP), the red-emission of bipyridine-Ru(II) complex was completely withheld. In aqueous media, HOCl can trigger an oxidation reaction to cleave the DNP moiety from the Ru(II) complex, which results in the formation of a highly luminescent bipyridine-Ru(II) complex derivative, [Ru(bpy)2(COOH-bpy)](PF6)2 (COOH-bpy: 4'-methyl-2,2'-bipyridyl-4-carboxylic acid), accompanied by a 190-fold luminescence enhancement. Cell imaging experimental results demonstrated that [Ru(bpy)2(DNPS-bpy)](PF6)2 is membrane permeable, and can be applied for capturing and visualizing the exogenous/endogenous HOCl molecules in living cell samples. The development of this Ru(II) complex probe not only provides a useful tool for monitoring HOCl in living systems, but also strengthens the application of transition metal complex-based luminescent probes for bioimaging.

Synthesis, structural characterization, and photophysical, spectroelectrochemical, and anion-sensing studies of heteroleptic ruthenium(II) complexes derived from 4'-polyaromatic-substituted terpyridine derivatives and 2,6-bis(benzimidazol-2-yl)pyridine

Heteroleptic bis-tridentate ruthenium(II) complexes of composition [(H2pbbzim)Ru(tpy-Ar)](ClO4)2, where H2pbbzim = 2,6-bis(benzimidazol-2-yl)pyridine and tpy-Ar = 4'-substituted terpyridine ligands with Ar = phenyl (2), 2-naphthyl (3), 9-anthryl (4), and 1-pyrenyl (5) groups, have been synthesized and characterized by using standard analytical and spectroscopic techniques. The X-ray crystal structures of the complexes [(H2pbbzim)Ru(tpy-Naph)](ClO4)2 (3), [(pbbzim)Ru(tpy-Naph)]·(CH3)2CO·H2O (3a), and [(H2pbbzim)Ru(tpy-Py)](ClO4)2 (5) have been determined. The absorption, steady-state, and time-resolved luminescence spectral properties of the complexes were thoroughly investigated in dichloromethane. The compounds display strong luminescence at room temperature with lifetimes (τ2) in the range of 5.5-62 ns, depending upon the nature of the polycyclic aromatic moiety as well as the solvents. The complexes are found to undergo one reversible oxidation in the positive potential window (0 to +1.5 V) and four successive quasi-reversible reductions in the negative potential window (0 to -2.4 V). The anion-sensing properties of the receptors were thoroughly investigated in acetonitrile/dichloromethane (1/9 v/v) solutions (2 × 10(-5) M) using absorption, steady-state, and time-resolved emission spectroscopic studies. (1)H NMR titration experiments, on the other hand, were carried out in either CD3CN or DMSO-d6. The anion-sensing studies revealed that the receptors act as sensors for F(-), CN(-), AcO(-), and SO4(2-) and to some extent for HSO4(-) and H2PO4(-). It is evident that, in the presence of excess anions, deprotonation of the imidazole N-H fragments of the receptors occurs, which is signaled by the change of color from yellow-orange to violet visible with the naked eye. From the absorption and emission titration studies the binding/equilibrium constants of the receptors with the anions have also been determined. Anion-induced lifetime quenching and/or enhancement make the receptors suitable lifetime-based sensors for selective anions. Cyclic voltammetric (CV) measurements of the compounds carried out in acetonitrile have provided evidence in favor of anion-dependent electrochemical responses with F(-) and AcO(-) ions. Spectroelectrochemical studies have also been carried out for both the protonated and deprotonated forms of the complexes in the range of 300-1200 nm. With successive oxidation of the Ru(II) center, replacement of MLCT bands by LMCT bands occurs gradually with observation of sharp isosbestic points in all cases.