Polypyridine Complexes Research Articles

Spectroscopic and electrochemical behavior of a supramolecular tetrapyridylporphyrin encompassing four terpyridine(oxalate)chloridoruthenium(II) complexes and its use in nitrite sensors

Supramolecular species combining ruthenium(II) polypyridines and tetrapyridylporphyrins (TPyP) have been employed in electrochemical and molecular sensing devices, because of their unique synergistic properties. In this work, a new tetraruthenated porphyrin, 4-TRoxPyP has been synthesised, encompassing four pyridine bridged [Ru(Cl-tpy)(ox)] complexes (Cl-tpy=chloroterpyridine, ox=oxalate ion). Such species exhibit characteristic electronic transitions of porphyrin and ruthenium polypyridine complexes, such as a Soret band at 414nm, Q bands at 514nm, 557nm and 588nm and a ruthenium-to-terpy charge-transfer band at 643nm. A typical tetraruthenated porphyrin redox process has been observed at 0.72V versus NHE, associated with the peripheral Ru3+/2+ complexes. Their thin films have been prepared by drop casting onto a glassy carbon electrode, and successfully employed in nitrite analysis, by monitoring the chronoamperometric response at the Ru3+/2+ redox gate. A linear relationship between the anodic peak current and concentration of the analyte has been observed from 0 to 0.10mmolL−1, with a nitrite detection limit of 7.60μmolL−1.

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study.

The synthesis and characterization of the donor-acceptor substituted cyclometalated ruthenium(II) polypyridine complex isomers [Ru(dpb-NHCOMe)(tpy-COOEt)](PF6) 1(PF6) and [Ru(dpb-COOEt)(tpy-NHCOMe)](PF6) 2(PF6) (dpbH = 1,3-dipyridin-2-ylbenzene, tpy = 2,2';6,2"-terpyridine) with inverted functional group pattern are described. A combination of resonance Raman spectroscopic and computational techniques shows that all intense visible range absorption bands arise from mixed Ru → tpy/Ru → dpb metal-to-ligand charge transfer (MLCT) excitations. 2(PF6) is weakly phosphorescent at room temperature in fluid solution and strongly emissive at 77 K in solid butyronitrile matrix, which is typical for ruthenium(II) polypyridine complexes. Density functional theory calculations revealed that the weak emission of 2(PF6) arises from a (3)MLCT state that is efficiently thermally depopulated via metal-centered ((3)MC) excited states. The activation barrier for the deactivation process was estimated experimentally from variable-temperature emission spectroscopic measurements as 11 kJ mol(-1). In contrast, 1(PF6) is nonemissive at room temperature in fluid solution and at 77 K in solid butyronitrile matrix. Examination of the electronic excited states of 1(PF6) revealed a ligand-to-ligand charge-transfer ((3)LL'CT) as lowest-energy triplet state due to the very strong push-pull effect across the metal center. Because of the orthogonality of the participating ligands, emission from the (3)LL'CT is symmetry-forbidden. Hence, in this type of complex a stronger push-pull effect does not increase the phosphorescence quantum yields but completely quenches the emission.

Luminescent Rhenium(I) and Iridium(III) Polypyridine Complexes as Biological Probes, Imaging Reagents, and Photocytotoxic Agents.

Although the interactions of transition metal complexes with biological molecules have been extensively studied, the use of luminescent transition metal complexes as intracellular sensors and bioimaging reagents has not been a focus of research until recently. The main advantages of luminescent transition metal complexes are their high photostability, long-lived phosphorescence that allows time-resolved detection, and large Stokes shifts that can minimize the possible self-quenching effect. Also, by the use of transition metal complexes, the degree of cellular uptake can be readily determined using inductively coupled plasma mass spectrometry. For more than a decade, we have been interested in the development of luminescent transition metal complexes as covalent labels and noncovalent probes for biological molecules. We argue that many transition metal polypyridine complexes display triplet charge transfer ((3)CT) emission that is highly sensitive to the local environment of the complexes. Hence, the biological labeling and binding interactions can be readily reflected by changes in the photophysical properties of the complexes. In this laboratory, we have modified luminescent tricarbonylrhenium(I) and bis-cyclometalated iridium(III) polypyridine complexes of general formula [Re(bpy-R(1))(CO)3(py-R(2))](+) and [Ir(ppy-R(3))2(bpy-R(4))](+), respectively, with reactive functional groups and used them to label the amine and sulfhydryl groups of biomolecules such as oligonucleotides, amino acids, peptides, and proteins. Additionally, using a range of biological substrates such as biotin, estradiol, and indole, we have designed luminescent rhenium(I) and iridium(III) polypyridine complexes as noncovalent probes for biological receptors. The interesting results generated from these studies have prompted us to investigate the possible applications of luminescent transition metal complexes in intracellular systems. Thus, in the past few years, we have developed an interest in the cytotoxic activity, cellular uptake, and bioimaging applications of these complexes. Additionally, we and other research groups have demonstrated that many transition metal complexes have facile cellular uptake and organelle-localization properties and that their cytotoxic activity can be readily controlled. For example, complexes that can target the nucleus, nucleolus, mitochondria, lysosomes, endoplasmic reticulum, and Golgi apparatus have been identified. We anticipate that this selective localization property can be utilized in the development of intracellular sensors and bioimaging reagents. Thus, we have functionalized luminescent rhenium(I) and iridium(III) polypyridine complexes with various pendants, including molecule-binding moieties, sugar molecules, bioorthogonal functional groups, and polymeric chains such as poly(ethylene glycol) and polyethylenimine, and examined their potentials as biological reagents. This Account describes our design of luminescent rhenium(I) and iridium(III) polypyridine complexes and explains how they can serve as a new generation of biological reagents for diagnostic and therapeutic applications.

A Bis(tridentate)cobalt Polypyridine Complex as Mediator in Dye‐Sensitized Solar Cells

AbstractDye‐sensitized solar cells equipped with cationic and neutral RuII‐based sensitizers [Ru(ddpd){tpy(COOH)3}]2+ [12+; ddpd = N,N′‐dimethyl‐N,N′‐di(pyridin‐2‐yl)pyridin‐2,6‐diamine, tpy(COOH)3 = 2,2″6′,2″‐terpyridine‐4,4′,4″‐tricarboxylic acid] and [Ru(ddpd){tpy(COOH)(COO)2}] (2) with and without the coadsorbent chenodeoxycholic acid were constructed with I3–/I– or the CoIII/II‐based redox mediators [Co(bpy)3]3+/2+ (33+/2+; bpy = 2,2′‐bipyridine) and [Co(ddpd)2]3+/2+ (43+/2+) in the presence of LiClO4 and 4‐tert‐butylpyridine. The best photovoltaic performance was achieved by using the 43+/2+ shuttle and the neutral sensitizer 2 without coadsorbent. The higher short‐circuit photocurrent density and higher electron recombination lifetimes obtained with this combination suggest slow electron recombination kinetics at the TiO2 surface with the CoIII complex 43+. The slow electron transfer to 43+ is tentatively ascribed to the high‐lying π* orbitals of the electron‐rich ddpd ligands, which result in a weak electronic coupling. This contrasts with the faster recombination with 33+, which features the low‐energy π* orbitals of the bpy ligands.

Bioorthogonal Labeling, Bioimaging, and Photocytotoxicity Studies of Phosphorescent Ruthenium(II) Polypyridine Dibenzocyclooctyne Complexes.

The synthesis, characterization, photophysics, lipophilicity, and cellular properties of new phosphorescent ruthenium(II) polypyridine complexes functionalized with a dibenzocyclooctyne (DIBO) or amine moiety [Ru(N^N)2 (L)](PF6 )2 are reported (L=4-(13-N-(3,4:7,8-dibenzocyclooctyne-5-oxycarbonyl) amino-4,7,10-trioxa-tridecanyl-aminocarbonyl-oxy-methyl)-4'-methyl-2,2'-bipyridine bpy-DIBO, N^N=2,2'-bipyridine bpy (1 a), 1,10-phenanthroline phen (2 a); L=4-(13-amino-4,7,10-trioxa-tridecanylaminocarbonyl-oxy-methyl)-4'-methyl-2,2'-bipyridine bpy-NH2 , N^N=bpy (1 b), phen (2 b)). The strain-promoted alkyne-azide cycloaddition (SPAAC) reaction of the DIBO complexes 1 a and 2 a with benzyl azide were studied. Also, the DIBO complexes 1 a and 2 a can selectively label N-azidoglycans located on the surface of CHO-K1 and A549 cells that were pretreated with 1,3,4,6-tetra-O-acetyl-N-azidoacetyl-D-mannosamine (Ac4 ManNAz). Additionally, the intracellular trafficking and localization of these biomolecules were monitored using laser-scanning confocal microscopy. Interestingly, the biolabeling and cellular uptake efficiency of the DIBO complexes 1 a and 2 a were cell-line dependent, as revealed by flow cytometry and ICP-MS. Furthermore, the complexes showed good biocompatibility toward the Ac4 ManNAz-pretreated cells in the dark, but exhibited photoinduced cytotoxicity due to the generation of singlet oxygen.

Dual-Emissive Cyclometalated Iridium(III) Polypyridine Complexes as Ratiometric Biological Probes and Organelle-Selective Bioimaging Reagents.

In this Article, we present a series of cyclometalated iridium(III) polypyridine complexes of the formula [Ir(N^C)2(N^N)](PF6) that showed dual emission under ambient conditions. The structures of the cyclometalating and diimine ligands were changed systematically to investigate the effects of the substituents on the dual-emission properties of the complexes. On the basis of the photophysical data, the high-energy (HE) and low-energy (LE) emission features of the complexes were assigned to triplet intraligand ((3)IL) and triplet charge-transfer ((3)CT) excited states, respectively. Time-dependent density functional theory (TD-DFT) calculations supported these assignments and indicated that the dual emission resulted from the interruption of the communication between the higher-lying (3)IL and the lower-lying (3)CT states by a triplet amine-to-ligand charge-transfer ((3)NLCT) state. Also, the avidin-binding properties of the biotin complexes were studied by emission titrations, and the results showed that the dual-emissive complexes can be utilized as ratiometric probes for avidin. Additionally, all the complexes exhibited efficient cellular uptake by live HeLa cells. The MTT and Annexin V assays confirmed that no cell death and early apoptosis occurred during the cell imaging experiments. Interestingly, laser-scanning confocal microscopy revealed that the complexes were selectively localized on the cell membrane, mitochondria, or both, depending on the nature of the substituents of the ligands. The results of this work will contribute to the future development of dual-emissive transition metal complexes as ratiometric probes and organelle-selective bioimaging reagents.

Steady-state and time-resolved luminescence of Ru(II) polypyridine complexes attached to Ag nanoparticles: Effect of chemisorption in comparison with electrostatic bonding

Steady state and nanosecond time resolved luminescence (namely, 3MLCT phosphorescence) of [Ru(bpy)3]2+ and of [Ru(bpy)2(dcbpy)]2+/bpy=2,2′-bipyridine; dcbpy=2,2′-bipyridyl-4,4′-dicarboxylic acid/attached to Ag NPs (the former by the electrostatic bonding, the latter by chemisorption) in non-aggregated Ag NP hydrosol systems has been investigated, and compared to the luminescence characteristics of the complexes in aqueous solutions. The intensity decrease of the 452nm (and/or 455nm, respectively) main band and elimination of the short wavelength shoulders in the excitation spectra and the intensity decrease of the emission spectra observed for both complexes upon their attachment to Ag NPs is attributed to the overlap of the excitation spectra with the surface plasmon extinction (SPE) of Ag NPs. The overlap leads to a loss of excitation energy by SPE as well as to a decrease of the 1MLCT to 3MLCT intersystem crossing efficiency. The time-resolved luminescence study shows that the 3MLCT phosphorescence lifetimes of both complexes are markedly (by 3 and 4 orders of magnitude, respectively) shortened upon their attachment to Ag NPs. Nevertheless, the 3MLCT lifetime of the chemisorbed [Ru(bpy)2(dcbpy)]2+ is by at least one order of magnitude shorter than that of the electrostatically bonded [Ru(bpy)3]2+, which indicates, that the phosphorescence lifetimes of these luminophores are strongly affected by the type of Ag NP surface–luminophore bonding.

English

English

Syntheses, spectral characterization, thermal properties and DNA cleavage studies of a series of Co(II), Ni(II) and Cu(II) polypyridine complexes with some new imidazole derivatives of 1,10-phenanthroline

In the present study three new imidazole derivatives of phen, 2-(4-hydroxy-3,5-diiodophenyl) imidazo[4,5-f][1,10]phenanthroline L1, 2-(2-hydroxy-3,5-diiodophenyl)imidazo[4,5-f][1,10]phenanthroline L2, 2-(4-hydroxy-5-iodo-3-methoxyphenyl)imidazo[4,5-f][1,10]phenanthroline L3 and their nine new polypyridine complexes[M(N–N)2(L1–3)](OAc)2·(nH2O) where M is Ni(II), Co(II) and Cu(II) and where (N–N)2 is 2,2′-bipyridine (bpy)2 or 1,10-phenanthroline (phen)2 have been synthesized from the reaction of the metal precursor complexes [M(phen)2(OAc)2]·(nH2O) and [M(bpy)2(OAc)2]·(nH2O) with the respective ligands in ethanol and water. The structures of the compounds were determined with the aid of elemental analysis and FT-IR, UV–Vis, 1H NMR, ESR spectroscopic methods, magnetic measurements and conductance measurements, further analyzed by powder XRD and thermal studies. Elemental analysis data suggested that the complexes have a 1:2:1 molar ratio among the metal and phen or bpy and L1/L2 or L3 ligands. The spectral data show that all the complexes were six coordinated and possess octahedral geometry around the metal ions. The X-band ESR spectrum of the Cu(II) in DMSO solution at room temperature was recorded and observed anisotropic g values indicate the presence of metal ion in an octahedral environment. The powder XRD patterns of complexes recorded in the range (2θ=0–80°) and average crystallite size (dXRD) was calculated using Scherrer’s formula. Thermal decomposition profiles of complexes show high decompound temperatures indicating a good thermal stability. Binding of the complexes with calf thymus DNA (CT DNA) has been investigated by gel electrophoresis. The experimental results indicate that the complexes bind to DNA by intercalation mode and found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation.

Acid–base effects, light emission, DNA-binding and photocleavage studies of oligo-homonuclear ruthenium(II) complexes and their computational study

The ground- and excited-state acid ionization constants and the DNA binding properties of mono-, di- and trinuclear ruthenium(II) polypyridine complexes have been studied by electronic absorption and fluorescence emission spectroscopy. The DNA binding abilities of the complexes increase with increasing π-electron multiplicity of phenanthroline groups and the H-bonding properties of imidazole moieties increase from the mononuclear (R1) to dinuclear (R2), followed by trinuclear (R3) complexes. In addition, the increasing surface area of the complexes relatively leads to a corresponding enhancement in binding affinity. The DNA-binding constants, Kb, of the complexes were determined systematically by spectrophotometric titration. In addition to the various ionic interactions, van der Waals interaction, hydrogen bonding, DNA-binding constants Kb and hypochromism of Ru(II) polypyridine complexes inferred the existence of intercalation mode of binding. The trend in DNA-binding affinities as well as the spectral properties of this series of complexes can be reasonably explained by applying the DFT at the B3LYP/LanL2DZ/6-31G level. The results suggest that the multiplication of complex unit has important effects on the electronic structures, a trend in the DNA-binding affinities and an improvement of spectral properties of the complexes. The binding affinity of the ruthenium complexes with biological receptors namely, G-quadraplexes from human telomeres has been investigated. The binding characteristics of complexes have been compared with each other using molecular docking. Further, these complexes tend to promote cleavage of plasmid DNA under photolytic conditions.

Highly stable and luminescent layered hybrid materials for sensitive detection of TNT explosives.

Self-assembly is an effective way to fabricate optical molecular materials. However, this strategy usually changes the nanoenvironment surrounding fluorescence molecules, yielding low luminescence efficiency. Herein, we report the intercalation of a ruthenium polypyridine (Ru) complex into the interlayer galleries of layered double hydroxides (LDHs), forming a Ru/LDH hybrid. The Ru complex exists as an ordered monolayer state, and the hybrid exhibits high thermal and photo stability. Its luminescence efficiency and lifetime are increased by ∼1.7 and ∼1 times, respectively, compared to those of free molecules. We constructed a Ru/LDH sensing platform based on a fluorescence quenching effect for highly sensitive detection of TNT with a detection limit of 4.4 μM.

Artificial photosynthesis: a molecular approach to photo-induced water oxidation

Abstract By the use of a molecular approach we performed photo-induced water oxidation by combining different photosensitizers and catalysts in order to obtain an efficient system that pave the way to the construction of an artificial photosynthetic system. Different types of molecular catalysts, such as ruthenium and vanadium polyoxometalates or cobalt core stabilized by different organic ligands were combined with ruthenium (II) polypyridine complexes of different nuclearity, mononuclear species like [Ru(bpy)3]2+ or a tetranuclear dendrimer.

Rhenium(I) polypyridine dibenzocyclooctyne complexes as phosphorescent bioorthogonal probes: Synthesis, characterization, emissive behavior, and biolabeling properties

We report the development of rhenium(I) polypyridine complexes appended with a dibenzocyclooctyne (DIBO) moiety as bioorthogonal probes for azide-modified biomolecules. Three phosphorescent rhenium(I) polypyridine DIBO complexes [Re(N^N)(CO)3(py-C6-DIBO)][CF3SO3] (py-C6-DIBO=3-(N-(6-(3,4:7,8-dibenzocyclooctyne-5-oxycarbonylamino)hexyl)aminocarbonyl)pyridine; N^N=1,10-phenanthroline (phen) (1a), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4-phen) (2a), 4,7-diphenyl-1,10-phenanthroline (Ph2-phen) (3a)) and their DIBO-free counterparts [Re(N^N)(CO)3(py-C6-BOC)][CF3SO3] (py-C6-BOC=3-(N-(6-(tert-butoxycarbonylamino)hexyl)aminocarbonyl)pyridine; N^N=phen (1b), Me4-phen (2b), Ph2-phen (3b)) were synthesized and characterized. Upon photoexcitation, all the complexes displayed intense and long-lived yellow triplet metal-to-ligand charge-transfer (3MLCT) (dπ(Re)→π*(N^N)) emission. The DIBO complexes underwent facile reactions with benzyl azide in methanol at 298K with second-order rate constants (k2) in the range of 0.077 to 0.091M−1s−1. As revealed from SDS-PAGE analysis, the DIBO complexes can selectively label azide-modified proteins and the resulting bioconjugates displayed strong phosphorescence upon photoexcitation. Results of inductively coupled plasma mass spectrometry (ICP-MS) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays indicated that the DIBO complexes accumulated in Chinese Hamster Ovary (CHO) cells with considerable cytotoxic activity. Upon incubation of CHO cells with these complexes, relatively weak intracellular emission was observed. In contrast, upon pretreatment of the cells with 1,3,4,6-tetra-O-acetyl-N-azidoacetyl-d-mannosamine (Ac4ManNAz), intense emission was observed from the cell membrane and some internal compartments. The results suggest that the DIBO complexes are promising candidates for imaging azide-labeled biomolecules.

ChemInform Abstract: Towards the Development of Functionalized Polypyridine Ligands for Ru(II) Complexes as Photosensitizers in Dye‐sensitized Solar Cells (DSSCs)

AbstractReview: 148 refs.

Syntheses and properties of phosphine-substituted ruthenium(II) polypyridine complexes with nitrogen oxides.

Four novel phosphine-substituted ruthenium(ii) polypyridine complexes with nitrogen oxides-trans(P,NO2)-[Ru(trpy)(Pqn)(NO2)]PF6 (trans-NO2), cis(P,NO2)-[Ru(trpy)(Pqn)(NO2)]PF6 (cis-NO2), [Ru(trpy)(dppbz)(NO2)]PF6 (PP-NO2), and cis(P,NO)-[Ru(trpy)(Pqn)(NO)](PF6)3 (cis-NO)-were synthesised (trpy = 2,2':6',2''-terpyridine, Pqn = 8-(diphenylphosphanyl)quinoline, and dppbz = 1,2-bis(diphenylphosphanyl)benzene). The influence of the number and position of the phosphine group(s) on the electronic structure of these complexes was investigated using single-crystal X-ray structural analysis, UV-vis absorption spectroscopy, and electrochemical measurements. The substitution lability of the nitrogen oxide ligand of each complex is discussed in comparison with that of the corresponding acetonitrile complexes.

Water oxidation catalysed by a mononuclear Co(II) polypyridine complex; possible reaction intermediates and the role of the chloride ligand.

A mononuclear cobalt(II) complex as a homogeneous molecular catalyst for photochemically, electrochemically and chemically induced oxygen evolution reactions is presented. Experimental evidence points towards the presence of a chloride ligand at the cobalt centre throughout the catalytic cycle, and the temporary detachment of a pyridine ligand to open a coordination site for substrate binding.

Rhenium(I) Polypyridine Complexes as Luminescence-Based Sensors for the BSA Protein

The binding interaction of rhenium(I) complexes fac-[Re(CO)3(NN)(py)]+, py = pyridine and NN = 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (ph2phen) or 4,7-dichloro-1,10-phenanthroline (Cl2phen), and bovine serum albumin (BSA) was investigated at physiological pH using emission intensity variation and circular dichroism (CD) spectroscopy. The photophysical investigations showed that in the presence of BSA, the metal-to-ligand-charge transfer (3MLCT) emission of the rhenium(I) complexes was quenched due to entrapment of the complex within the protein environment. Additionally, high Stern-Volmer (KSV) and binding (Kb) constants were determined from luminescence data, revealing the occurrence of a strong interaction and/or association. The differences in KSV values can be tentatively associated with an electron-withdrawing constant (σ) defined by Hammett equation. The CD results showed that the extent of α-helicity of the BSA decreased upon the addition of rhenium complexes, which provided further support for the interaction of rhenium(I) complexes and the protein.

Modification of 1,2,4,5-tetrazine with cationic rhenium(I) polypyridine units to afford phosphorogenic bioorthogonal probes with enhanced reaction kinetics.

New phosphorogenic bioorthogonal probes derived from mononuclear and binuclear rhenium(I) polypyridine complexes containing a 1,2,4,5-tetrazine moiety were designed; these complexes displayed substantial dienophile-induced emission enhancement, and accelerated reaction kinetics and could target a protein conjugate in living cells.

Functionalization of cyclometalated iridium(iii) polypyridine complexes for the design of intracellular sensors, organelle-targeting imaging reagents, and metallodrugs

We summarize the biological applications of selected organometallic iridium(iii) complexes as intracellular sensors, organelle-targeting imaging reagents, and metallodrugs.

A family of Ru(ii) complexes built on a novel sexipyridine building block: synthesis, photophysical properties and the rare structural characterization of a triruthenium species

A new tris-2'',4'',6''-(2,2'-bipyridin-4-yl)-1'',3'',5''-triazine ligand and its family of ruthenium coordination complexes are described along with their characterization by electrochemical and photophysical methods as well as a rare single crystal X-ray analysis of a triruthenium polypyridine complex.