Photostability of luminescent ruthenium(II) complexes in polymers and in solution

The effects of oxygen on the photochemical properties of ruthenium(II) complexes in solution and in polymers are reported. In solution, the complex is actually protected from decomposition by the presence of oxygen as a result of deactivation of the complex by oxygen quenching before it can undergo ligand loss by monomolecular dissociation; however, in polymers, the presence of oxygen increases photochemical decomposition. Singlet molecular oxygen, a product of the oxygen quenching process, may attack the ground state complex or triplet oxygen may directly attack the excited state of the complex. Both mechanisms may be involved in the photodestruction of the complex. The role of oxygen in the photodecomposition was examined by monitoring the photochemical decomposition of various complexes of different singlet oxygen reactivity, as well as absorption and mass spectroscopy studies. It is suggested that in polymers, unlike in solutions, the newly formed reactive singlet oxygen is not able to diffuse away from the complex. The singlet oxygen, trapped in close proximity to the metal complex, has an enhanced opportunity to attack it. This cage effect is supported by studies using tris(1,10-phenanthroline)ruthenium(II) in poly(ethylene glycol) of increasing molecular weight to create an increasingly constraining cage around the complex. Increased poly(ethylene glycol) molecular weight leads to increased oxygen attack of the complex, supporting the cage effect.     

Quenching of luminescent ruthenium(II) complexes by water and polymer-based relative humidity sensors

Water quenching of luminescent [Ru(phen)(2)dppz]Cl(2), [Ru(phen)(2)dppn]Cl(2), and [Ru(4,7-Ph(2)phen)(2) dppz]Cl(2) (phen = 1,10-phenanthroline; 4,7-Ph(2)phen = 4; 4,7-diphenyl-1,10-phenanthroline; dppz = dipyrido[3,2-a:2'3'-c]phenazine; dppn = benzodipyrido(a:3,2-h:2',3'-j)phenazine) complexes was studied in acetonitrile and in polymers. The polymers contained hydrophobic and hydrophilic components to control mechanical properties and were designed to absorb water with changing humidity and, thus, affect the emission intensity and lifetime. Quenching by water in mixed solvents and in polymers was shown to arise from a combination of diffusional and static ground-state associational quenching. The factors controlling polymer properties are discussed. The systems can be tailored to give a wide range of responses or function as a binary sensor at a fixed humidity level.     

Simple and selective sensing of cysteine using gold nanoparticles modified by ruthenium(II) complexes

A simple and selective luminescence sensing method for the cysteine detection was developed based on gold nanoparticles modified by the new ruthenium(II) complexes. The intense emission of the modified ruthenium(II) complexes was quenched efficiently by gold nanoparticles due to the energy and charge transfer between the ruthenium(II) fluorophores and gold nanoparticles. Upon addition of cysteine, the emission of the ruthenium(II) complexes was enhanced significantly by the release of the ruthenium(ll) complexes from the surface of the gold nanoparticles. Therefore, cysteine could be detected by this gold nanoparticles-ruthenium(II) complexes based probes. The synthesis of gold nanoparticles and the modification based fluorophores probed could be accomplished successfully within one step, which simplified the preparation of luminescence sensors. Moreover, since metal-to-ligand charge transfer transition (3MLCT) emission band of the ruthenium(II) complexes was in the visible region, this approach was available for biomolecular sensing applications, and its relatively long life time made it suitable for the biological process studies.     

Light-emitting devices based on ruthenium (II) bipyridine complexes coupled with cadmium sulfide nanoparticles

The fabrication of a light-emitting device based on a composite consisting of cadmium sulfide nanoparticle, poly(vinylalcohol), and ruthenium 2,2'-bipyridyl complex is reported. The electroluminescence spectrum of this composite is similar to the combination of the emission from ruthenium complexes and cadmium sulfide. A stable electroluminescence at low threshold voltage (4 V), with a brightness of 680 cd/m2 and an external quantum efficiency of approximately 0.2% was achieved. it was demonstrated that the cadmium sulfide nanoparticles were able to improve the performance of the device and enhance the electron carrier mobility as compared to the device based on pure ruthenium complex.     

Studies of molecular recognition mechanism in supramolecular system of ruthenium(II) polypyridyl complexes and DNA

The recent studies on supramolecular system assembled by Ru(II) polypyridyl complexes and B-form double-stranded DNA is reviewed. These complexes have been studied as DNA spectroscopic tags and structural probes. The studies focus on the recognition parameters of these complexes binding to DNA, including the influence of the shape and size of intercalative ligand, the ancillary ligands and the effects of hydrogen bonding. Enantioselectivities of these complexes binding to DNA are also briefly discussed.     

Evaluation of reproductive toxicity in male rats treated with novel synthesized ruthenium(II) and gold(I)-NHC complexes

In this study, we aimed to determine the reproductive toxicity in rat induced by ruthenium(II)-NHC (Ru^II) and gold(I)-NHC (Au^I) complexes that have anticarcinogenic effects. For this purpose, 35 Sprague–Dawley rats were randomly divided into 5 equal groups. In control group, rats treated with saline, Ru^II, and Au^I complexes were intraperitoneally given high (10?mg/kg) and low (5?mg/kg) doses to rats via a one-time administration. The animals were sacrificed, and testis tissues were taken on Day 10 of the drug administration for the determination of the biochemical, histopathological, spermatological, and hormonal parameters. It was determined that treatment group that was subjected to treatment using both Ru^II and Au^I complexes significantly caused oxidative, histopathological, spermatological, and hormonal damage compared to control group. However, the sexual and accessory organ weight did not significantly change when compared to control. In addition, it was shown that Au^I treatment generally caused more adverse effects than Ru^II treatment in a dose-dependent manner. In conclusion, when these synthesized compounds are used for the treatment of cancer, they could cause toxic effects on male reproductive system and lead to infertility. However, Ru^II complex is a more preferable option in cancer treatment, particularly in terms of user safety.     

Evaluation of reproductive toxicity in male rats treated with novel synthesized ruthenium(II) and gold(I)-NHC complexes

In this study, we aimed to determine the reproductive toxicity in rat induced by ruthenium(II)-NHC (Ru(II)) and gold(I)-NHC (Au(I)) complexes that have anticarcinogenic effects. For this purpose, 35 Sprague-Dawley rats were randomly divided into 5 equal groups. In control group, rats treated with saline, Ru(II), and Au(I) complexes were intraperitoneally given high (10?mg/kg) and low (5?mg/kg) doses to rats via a one-time administration. The animals were sacrificed, and testis tissues were taken on Day 10 of the drug administration for the determination of the biochemical, histopathological, spermatological, and hormonal parameters. It was determined that treatment group that was subjected to treatment using both Ru(II) and Au(I) complexes significantly caused oxidative, histopathological, spermatological, and hormonal damage compared to control group. However, the sexual and accessory organ weight did not significantly change when compared to control. In addition, it was shown that Au(I) treatment generally caused more adverse effects than Ru(II) treatment in a dose-dependent manner. In conclusion, when these synthesized compounds are used for the treatment of cancer, they could cause toxic effects on male reproductive system and lead to infertility. However, Ru(II) complex is a more preferable option in cancer treatment, particularly in terms of user safety.     

Oxygen-sensing properties of ormosil hybrid materials doped with ruthenium(II) complexes via a sol-gel process

Organically modified silicate (ormosil) materials doped with [4,4′-dimethyl-2,2′-bipyridine-bis(2,2′-bipyridine)] ruthenium(II) dichloride ([Ru-mbpy]²⁺) and [4,4′-dimethylformate-2,2′-bipyridine-bis(2,2′-bipyridine)] ruthenium(II) dichloride ([Ru-dmfbpy]²⁺) were prepared by a sol-gel procedure for oxygen-sensing applications. The results indicated that the concentrations of the Ru(II) diimine complexes obviously influenced the linearity of Stern-Volmer plots (I₀ /I vs. O₂%). The best suitable concentrations of [Ru-mbpy]²⁺ and [Ru-dmfbpy]²⁺ in the sol for oxygen sensors were found to be 1.0 × 10^− 3 M and 2.5 × 10^− 3 M, respectively. The fluorescence quenching time and recovery time of oxygen sensor doped with [Ru-mbpy]²⁺ (1.0 × 10^− 3 M) were 18 s and 38 s and those doped with [Ru-dmfbpy]²⁺ (1.0 × 10^− 3 M) were 13 s and 32 s, respectively. The oxygen sensor based on Ru(II) complex modified by esterification demonstrated excellent linear calibration relationship and improved long-term stability.     

Redox switchable self-assembled monolayers of functional ruthenium(III/II) complexes on optically transparent platinum electrodes

Self-assembled monolayers (SAMs) of functional Ru^II complexes on optically transparent ultrathin Pt films (10-nm nominal thicknesses) have been prepared. We have demonstrated that reversible Ru^III/II redox switching of these SAMs can be achieved by using appropriate oxidizing or reducing agents. Such a switching in molecular properties has been simply detected by transmission spectroscopy with a conventional spectrophotometer following the appearance/disappearance of the optical absorption metal-to-ligand charge-transfer (MLCT) band in the visible region. In light of their potential multifunctional properties, these SAMs on an optically transparent metal electrode are appealing candidates in the perspective of integrated molecular switch nanodevices.     

Electrochemiluminescence of ruthenium (II) tris(bipyridine) encapsulated in sol-gel glasses

The electrogenerated chemiluminescence (ECL) of Ru(bpy)3 2+ and tripropylamine, tributylamine, triethylamine, trimethylamine, or sodium oxalate encapsulated within sol-gel-derived silica monoliths have been investigated using an immobilized ultramicroelectrode assembly. The major purpose of this study was to investigate the role of the reductant on the magnitude and stability of the ECL in this solid host matrix. For gel-entrapped Ru(bpy)3 2-/tertiary amines, the shape and intensity of the ECL-potential curves were highly dependent on scan rate. At 10 mV/s, the ECL intensity was ca. 6-fold higher relative to that observed at 500 mV/s. When the ECL acquired at low scan rates was normalized by that obtained in solution under similar conditions, a value of 0.03-0.06 was obtained. In direct contrast, the ECL of the Ru(bpy)3 2+-oxalate system showed little dependence on scan rate, and the ECL was ca. 65-75% of that measured in solution. These differences can be attributed to differences in rotational and translational mobility between the reductants (amines vs oxalate) trapped in this porous solid host For both systems, the ECL was found to be stable upon continuous oxidation or upon drying the gels in a high-humidity environment for over 10 days.     

Novel heteroleptic ruthenium (II) complex with DPBPZ derivative for dye-sensitized solar cells

Herein, as Ru(II) complex for the dye-sensitized solar cells (DSSCs), we designed and investigated a novel heteroleptic ruthenium complex [Ru(dcbpy)(dpbpz)(NCS)2] with dpbpz derivative to enhance photovoltaic performance. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to gain insight into the factors responsible for photovoltaic properties as dye sensitizer. Molecular orbitals analysis confirmed that HOMO of [Ru(dcbpy)2(NCS)2] and [Ru(dcbpy)(dpbpz)(NCS)2] are delocalized over the ruthenium t2g character with sizable contribution from the NCS ligand orbitals. The LUMO of [Ru(dcbpy)2(NCS)2] is localized over the dcbpy moiety. However, LUMO of [Ru(dcbpy)(dpbpz)(NCS)2] is localized over the dpbpz moiety and LUMO + 1 is localized the dcbpy moiety. Overall, the absorption spectrum of the present Ru complex was more broad than that of [Ru(dcbpy)2(NCS)2] known as N3 dye. Especially, absorption band in the region between 500 nm and 600 nm was red-shifted. Moreover, the distance between the HOMO of [Ru(dcbpy)(dpbpz)(NCS)2] and the anchoring moiety is longer than that of [Ru(dcbpy)2(NCS)2]. This means that [Ru(dcbpy)(dpbpz)(NCS)2] have longer charge-separated lifetime than [Ru(dcbpy)2(NCS)2. These results are attributed to the extended pi-conjugation of dpbpz moiety. Therefore, we suggest that newly designed [Ru(dcbpy)(dpbpz)(NCS)2] heteroleptic ruthenium complex would be a good candidate as a dye sensitizer of DSSCs, comparable to [Ru(dcbpy)2(NCS)2].     

Atomic layer deposition of Ru films from bis(2,5-dimethylpyrrolyl)ruthenium and oxygen

Ru thin films were grown on hydrogen terminated Si, SiO₂, Al₂O₃, HfO₂, and TiO₂ surfaces by atomic layer deposition from bis(2,5-dimethylpyrrolyl)ruthenium precursor and oxygen. The 4-20 nm thick films on these surfaces consisted of nanocrystalline hexagonal metallic ruthenium, regardless of the deposition temperature. At the lowest temperatures examined, 250-255 °C, the growth of the Ru films was favored on silicon, compared to the growth on Al₂O₃, TiO₂ and HfO₂. At higher temperatures the nucleation and growth of Ru became enhanced in particular on HfO₂, compared to the process on silicon. At 320-325 °C, no growth occurred on Si-H and SiO₂-covered silicon. Resistivity values down to 18 μΩ·cm were obtained for ca. 10 nm thick Ru films.     

Zn(II), Cd(II) and Hg(II) complexes of N-methyl-N-phenyl dithiocarbamate as single-source precursors for the synthesis of metal sulfide nanoparticles

Zn(II), Cd(II) and Hg(II) complexes of N-methyl-N-phenyl dithiocarbamate have been used as single source precursors to synthesize hexadecylamine capped ZnS, CdS and HgS nanoparticles and their structural and optical properties determined. The optical spectra of the prepared nanoparticles show a blue shift which is a characteristic of particles in their nanometric domain. The sizes of the prepared nanoparticles were estimated as 4.7, 6.2 and 18.0 nm for the ZnS, CdS, and HgS samples respectively.     

Miniaturized tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence detection cell for capillary electrophoresis and flow injection analysis

The design and performance of a miniaturized chip-type tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)3(2+)] electrochemiluminescence (ECL) detection cell suitable for both capillary electrophoresis (CE) and flow injection (FI) analysis are described. The cell was fabricated from two pieces of glass (20 x 15 x 1.7 mm), and the 0.5-mm-diameter platinum disk was used as working electrode held at +1.15 V (vs silver wire quasi-reference), the stainless steel guide tubing as counter electrode, and the silver wire as quasi-reference electrode. The performance traits of the cell in both CE and FI modes were evaluated using tripropylamine, proline, and oxalate and compared favorably to those reported for CE and FI detection cells. The advantages of versatility, sensitivity, and accuracy make the device attractive for the routine analysis of amine-containing species or oxalate by CE and FI with Ru(bpy)3(2+) ECL detection.     

Competitive adsorption of copper(II), cadmium(II), lead(II) and zinc(II) onto basic oxygen furnace slag

Polluted and contaminated water can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a solution system will be affected by the presence of other metals. In this study, we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto basic oxygen furnace slag (BOF slag) in single- and multi-element solution systems as a function of pH and concentration, in a background solution of 0.01M NaNO(3). In adsorption edge experiments, the pH was varied from 2.0 to 13.0 with total metal concentration 0.84mM in the single element system and 0.21mM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH(50) (the pH at which 50% adsorption occurs) was found to follow the sequence Zn>Cu>Pb>Cd in single-element systems, but Pb>Cu>Zn>Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on BOF slag. The adsorption and potentiometric titrations data for various slag-metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 6.5 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II), Pb(II) and Zn(II) systems.     

N-alkylthioureacadmium (II) complexes as novel precursors for the synthesis of CdS nanoparticles

The cadmium(II) complexes of thiourea and N-alkylthioureas (with alkyl group methyl or ethyl) have been used as precursors for the preparation of TOPO-capped CdS nanoparticles. The precursors are air-stable, easy to prepare and inexpensive. These compounds decompose cleanly to give good quality crystalline materials. The nanoparticles obtained showed quantum confinement effects in their optical spectra and close-to-band-edge emission in luminescence experiments. The broad diffraction patterns and the diffuse rings observed in the SAED patterns are typical of nanometric particles. The TEM images showed agglomerates of needle-like plates of particles. The presence of a strong phosphorus peak in the EDAX spectra is indicative of TOPO bound to the surface.     

Studies on copper(II)- and zinc(II)-mixed ligand complexes of humic acid

Interactions between humic acid (HA), extracted from Brazilian peat soil, and cations of copper(II) and zinc(II) have been examined by infrared spectroscopy, and electrochemical and thermogravimetric analyses. Spectral studies revealed that the interaction with metals occurred mainly at the carboxylic acid groups of HA. The stability constants of HA complexes formed with Cu(2+) and Zn(2+) were found, by square wave voltammetry and application of the Lingane model, to be 8.93 x 10(10) and 2.92 x 10(2), respectively. Thermal analysis indicated that the stability of HA was increased by the presence of divalent cations of copper and zinc.     

The effects of nonionic surfactants on the tris(2,2'-bipyridyl)ruthenium(II)--tripropylamine electrochemiluminescence system

The electrochemistry and electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl) were studied in the presence of the nonionic surfactants Triton X-100, Thesit, and Nonidet P40. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine in both aqueous and surfactant solutions. Increases in both ECL efficiency (> or =8-fold) and duration of the ECL signal were observed in surfactant media. A shift to lower energies of the Ru(bpy)3(2+) ECL emission by approximately 8 nm was also observed. The one-electron oxidation of Ru(bpy)3(2+) to Ru(bpy)3(3t) occurs at + 1.03 V vs Ag/AgCl in aqueous buffered (0.2 M potassium phosphate) solution as found by square wave voltammetry. This potential did not shift in surfactant systems, indicating that the redshifts in ECL emission are due to stabilization of ligand pi* orbitals in the metal-to-ligand charge-transfer excited state. These results are consistent with hydrophobic interactions between Ru(bpy)3(2+) and the nonionic surfactants.     

Electrogenerated chemiluminescence of tris (2,2'-bipyridyl)ruthenium(II) ion-exchanged in nafion-silica composite films

The voltammetry and electrogenerated chemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3 2+) ion-exchanged in Nafion and Nafion-silica composite materials have been investigated. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved reactivity and long-term stability. Nation-silica composite materials with varying contents of Nation (53-100 wt% relative to silica) were prepared via the two-step acid/base hydrolysis and condensation of tetramethoxysilane. The Nafion doped sols were spin cast on glassy carbon electrodes, dried, and then ion-exchanged with Ru(bpy)3 2+. The shapes of the cyclic voltammetric curves and the amount of Ru(bpy)3 2+ exchanged into the films strongly depends on the amount of Nafion incorporated into the hybrid sol. Nafion-silica films with a low content of Nafion ion-exchanged less Ru(bpy)3 2+ and exhibited tail-shaped voltammetry at 100 mV/s. The ECL of immobilized Ru(bpy)3 2+ in the presence of either tripropylamine or sodium oxalate in pH 5 acetate buffer was also strongly dependent on the amount of Nafion introduced into the composite with greater ECL observed for the Nafion-silica films relative to pure Nafion.