Effects of Processing Temperature on the Oxygen Quenching Behavior of Tris(4,7′-diphenyl-1,10′-phenanthroline) Ruthenium (II) Sequestered Within Sol-Gel-Derived Xerogel Films

Sol-gel processing methods offer novel pathways for tailoring glasses. Amongst the issues that have received the least attention are the effects of the curing temperature on the behavior and photophysics of a dopant molecule sequestered within a sol-gel-derived xerogel. Of particular interest to our group are the effects of processing variables on the ability of a dopant molecule, that is sequestered within a xerogel glass, to be accessed by an analyte and the distribution of the dopant sites within the xerogel. The thermal stability of the luminophore tris(4,7-diphenyl-1,10-phenanthroline) ruthenium (II) ([Ru(dpp)₃]²⁺) provides a convenient way to address these issues and develop an understanding of how one might best exploit curing temperature to construct improved chemical sensors. This paper focuses on quantifying how the film curing temperature affects the spectroscopy and O₂ quenching of ([Ru(dpp)₃]²⁺) sequestered within sol-gel-derived xerogel thin films. Our quenching data on films once they have been cured demonstrate that there is a dramatic increase in the sensitivity of the ([Ru(dpp)₃]²⁺) molecules to O₂ quenching when the films have been cured at elevated temperatures. This arises primarily because there are two main types of ([Ru(dpp)₃]²⁺) microenvironments within the glass and higher temperature curing leads to an increase in the bimolecular quenching rate between O₂ and ([Ru(dpp)₃]²⁺). This is accomplished as follows. Below a curing temperature of 100–150°C, 15% of the xerogel-doped ([Ru(dpp)₃]²⁺) molecules are not accessed to any detectable degree by the O₂ molecules during the ([Ru(dpp)₃]²⁺) excited-state luminescence lifetime. However, as the xerogel is cured at or above 150°C, residual silanol-bound waters (or other impurities) dissociate from the xerogel and those ([Ru(dpp)₃]²⁺) molecules that were initially inaccessible become accessible to O₂. The dissociation of these water molecules, plus other events, also causes the originally inaccessible ([Ru(dpp)₃]²⁺) population to ultimately exhibit a quenching rate that is greater than the fraction of initially accessible ([Ru(dpp)₃]²⁺) molecules that were formed under ambient curing conditions.     

The role of precursors in the structure of SiO2-Al2O3 sols and gels by the sol-gel process

Binary sols and gels of SiO₂-Al₂O₃ were prepared using tetraethyl orthosilicate and each of four aluminum compounds; aluminum di (sec-butoxide) ethylacetoacetic ester chelate (AC), aluminum nitrate nonahydrate (AN), aluminum formoacetate (AF), and boehmite sol (BS) made from aluminum i-propoxide. The structure and the evolution of the Si-O-Al bonds in SiO₂-Al₂O₃ sols and gels were investigated by ²⁷Al nuclear magnetic resonance (NMR), Infrared absorption spectra, DTA, and X-ray diffraction. The formation of Si-O-Al bonds differs depending on the aluminum compounds used as raw materials. The ratio of Al(IV) to {Al(IV) + Al(VI)} is related to the microstructural homogeneity of the gels. When AC is used as a raw material, the Si-O-Al bonds are formed in the sol state and resultant gel shows good microstructural homogeneity. In case of AN, the Si-O-Al bonds are not formed either in the sol or the wet gel state. The bonds are formed by drying the gel before heat-treatment temperature reaches 300 400°C, resulting in good microstructural homogeneous gel. When AF is used, the Si-O-Al bonds are formed in the sol state but the ratio of Al(IV) to {Al(IV) + Al(VI)} is lower than when using AC. Microstructural homogeneity of the gel is ranked between AC or AN and BS. Using BS, the Si-O-Al bonds are not formed in the sol solution, and the change in the coordination number of the gel is similar to that of boehmite gel. The Microstructural homogeneity of the gel is the worst among the BS gels, which were prepared by using the four aluminum raw materials.     

Preparation of nanostructured porous SiO2-Al2O3 oxycarbonitride materials obtained by a new chemical precursor method

Nanostructured hybrid materials containing Al₂O₃ were synthesized via a sol-gel method through hydrolysis and co-condensation reactions using trimethylsilyl isocyanate (TMSI) as a new silica source in the presence of tetramethoxysilane (TMOS) and three different quantities (10, 20 and 30 wt.%) of aluminum sec-butoxide (Al(OBu^sec)₃ as a modifying agent. The xerogel nanostructured materials are pyrolyzed in nitrogen atmosphere in the temperature range from 400°C to 1100°C. The transformation of the xerogel hybrid networks into Al-Si oxycarbonitride materials has been investigated by XRD, FTIR, SEM, AFM, and ²⁹Si MAS-NMR. To the best of our knowledge, the work reported here is the first synthesis of porous di-urethanesils modified with aluminum and one of the few examples of alumosilica oxycarbonitride materials      

[Ru(bpy)3] nanocomposites containing heteropolyacids: Simple preparation and stable solid-state electrochemiluminescence detection application

In order to solidify the electrochemiluminescence (ECL) luminophor tris(2,2′-bipyridyl) ruthenium(II) ([Ru(bpy)₃]²⁺) onto the electrode surfaces robustly, the negative charged heteropolyacids (HPAs) moieties were utilized to attract and bond cations [Ru(bpy)₃]²⁺ via an adsorption method. The compositions and microstructures of the hybrid complexes were characterized by elemental analysis (EDS), spectroscopic techniques (UV-vis, FTIR) and field-emission scanning electron microscopy (FE-SEM). The electrochemical and ECL behaviors of the [Ru(bpy)₃]²⁺/[PW₁₂O₄₀]³⁻ hybrid complex contained in the solid film of the nanocomposites formed on the electrode surfaces were also studied. It was found that the corresponding solid membranes exhibited a diffusion-controlled voltammetric feature and excellent electrochemiluminescence behaviors. Hence potential prospects as new electrochemiluminescent materials for application in electroanalytical detection are envisioned.     

Electrochemiluminescent metallopolymers: Tuning the emission wavelength by energy transfer between two bound centres

The electrochemical and photonic properties of a metallopolymer in which both [Ru(dpp)₂Cl]⁺ (N5Cl) and [Ru(dpp)₂]²⁺ (N6) moieties are coordinated to a poly(4-vinylpyridine) backbone are described, dpp is 4,7-diphenyl-1,10-phenanthroline. Cyclic voltammetry and luminescence studies indicate that approximately 2% of centres are bis-coordinated to the PVP backbone, i.e., 2% are [Ru(dpp)₂]²⁺. When dissolved in ethanol or acetonitrile, two photoluminescence peaks are observed, at 620 and 720 nm corresponding to the N6 and N5Cl moieties, respectively. This dual emission indicates that the two centres communicate weakly in solution. In contrast, in aqueous solution or in thin films, a single emission band at 720 nm is observed suggesting efficient energy transfer to the N5Cl moiety. Polymer films generate electrochemiluminescence in the presence of oxalate as a co-reactant with an emission maximum at 730 nm corresponding to emission from the N5Cl centres alone.     

Redox,spectroscopic, photo-induced ligand exchange,and DNA interaction studies of a new Ru(II)Pt(II) bimetallic complex

A new bimetallic complex, [Ru(biq)₂(dpp)PtCl₂](PF₆)₂ (where biq = 2,2′-biquinoline and dpp = 2,3-bis(2-pyridyl)pyrazine), containing a cis-PtCl₂ moiety coupled to a sterically strained Ru(II)-based chromophore was designed, synthesized, and investigated with respect to its spectroscopic, redox, photo-induced ligand exchange, and DNA-interaction properties. The electrochemistry of the designed complex was found to be consistent with the bridging coordination of the dpp ligand and formation of the bimetallic complex. The complex displays intense ligand-based π → π* transitions in the UV region and metal-to-ligand charge-transfer transitions (MLCT) in the visible region. The loss of bridging coordination of the dpp ligand and formation of complexes, [Ru(biq)₂(CH₃CN)₂]²⁺ and [Pt(dpp)(CH₃CN)₂]²⁺ was observed when an acetonitrile solution of the metal complex was irradiated with visible light (λ_irr ≥ 550 nm). The designed complex displays covalent binding with DNA in dark through the cis-PtCl₂ moiety, as confirmed by agarose gel electrophoresis. Upon photoirradiation, the complex dissociates into two DNA-binding moieties and displays covalent binding through: (i) a cis-PtL₂ subunit of [Ptdpp(L)₂]²⁺ and (ii) open coordination sites of the ruthenium of [Ru(biq)₂(L)₂]²⁺ (L = solvent). The designed complex represents the first Ru(II)Pt(II) complex that undergoes photo-induced ligand exchange and displays multifunctional interactions with DNA upon photoirradiation.     

Synthesis of high surface area nanocrystalline anatase-TiO2 powders derived from particulate sol-gel route by tailoring processing parameters

Stabilised titania sols were prepared using an additive free particulate sol-gel route, via electrostatic stabilisation mechanism, with various processing parameters. Peptisation temperature, 50°C and 70°C, and TiO₂ concentration, 0.1, 0.2 and 0.4 molar, were chosen as processing parameters during sol preparation. Results from TiO₂ particle size and zeta potential of sols revealed that the smallest titania hydrodynamic diameter (13 nm) and the highest zeta potential (47.7 mV) were obtained for the sol produced at the lower peptisation temperature of 50°C and lower TiO₂ concentration of 0.1 M. On the other hand, between the sols prepared at 70°C, smaller titania particles (20 nm) and higher zeta potential (46.3 mV) were achieved with increasing TiO₂ concentration up to 0.4 M. X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) results of produced powders annealed at different temperatures showed that the 300°C annealed powder made from 0.1 M sol prepared at 50°C was a mixture of anatase and brookite, corresponding to a major phase of anatase (∼95% estimated), with the smallest average crystallite size of 1.3 nm and the highest specific surface area (SSA) of 193 m²/g. Furthermore, increasing TiO₂ concentration up to 0.4 molar for the sols prepared at 70°C resulted in decreasing the average crystallite size (1.9 nm at 300°C) and increasing SSA (116 m²/g at 300°C) of the powders annealed at different temperatures. Anatase-to-rutile phase transformation temperature was increased with decreasing peptisation temperature down to 50°C, whereas TiO₂ concentration had no effect on this transition. Anatase percentage increased with decreasing both peptisation temperature and TiO₂ concentration. Such prepared powders can be used in many applications in areas from photo catalysts to gas sensors.     

Spectroscopic and photoelectrochemical differences between racemic and enantiomeric [Ru(phen)3] ions intercalated into layered niobate K4Nb6O17

Chirality effects have been observed in the intercalation, spectroscopic and photoelectrochemical behavior when enantiomeric and racemic [Ru(phen)₃]²⁺ complexes were intercalated in the interlayer spaces of K₄Nb₆O₁₇. The results were interpreted in terms of a [Nb₆O₁₇]⁴⁻-chelate and chelate–chelate interactions. The faster luminescence decay and higher photocurrent of the enantiomeric [Ru(phen)₃]²⁺–K₄Nb₆O₁₇ compounds than the racemic ones suggest that the emission of adsorbed [Ru(phen)₃]²⁺ ions was not only quenched by adsorbed complexes (or concentration quenching) but also by the semiconductive host lattices.     

Colloid stability of electrostatically stabilized sols

 The dependence of the stability of SiO₂ and Al₂O₃ sols on the pH of their medium has been studied. Vapor adsorption isotherms on powders were prepared from acidic and basic sols, the immersion enthalpy (heat) of samples containing preadsorbed water have been determined and, also, the reversibility of the sol ⇌ xerogel transformation, i.e. the peptizability of the powders, has been investigated. Based on the flocculation values determined with KCl, the sols have been classified into three groups. The stability of highly hydrophilic sols (acidic SiO₂- and Al₂O₃-sols) is ensured by a thick continuous diffuse lyosphere formed around the particles, as the continuity principle by Ostwald–Buzágh suggests. In this case, no electric charge is needed for ensuring stability. These sols are thermodynamically stable (group 1). Sols with medium stability are stabilized by the electrical double layer around the particles and by 1–2 layers of adsorbed water. The flocculation value of these sols is determined by the electrostatic interaction, whereas the peptizability of the flocs is related to formation of water layers. Such sols are the basic SiO₂- and Al₂O₃-sols (group 2). Sols of low stability are of hydrophobic nature. Their flocculation value with 1:1 electrolytes is smaller than 0.1 molkg^-1. The transformation process sol ⇒ floccule ⇒ xerogel is mostly irreversible. There are a lot of such sols (group 3). The existence of a hydrosphere is proved by the almost identical value of the hydration energy for both the acidic and the basic SiO₂ sols, in spite of an order of magnitude difference in the flocculation value. The remnants of adsorbed water after drying hinders sintering of the particles and ensures the peptizability of powders. The highly hydrophilic sols (sequence of hydrophilicity: SiO₂> Al₂O₃>FeO OH ⋅ 0.5 H₂O) are all oxides which are formed in acidic media. Received: 25 May 1997 Accepted: 13 October 1997     

Sol–gel process of ZnO and ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> coated aluminum borate whiskers

Zinc nitrate and citric acid were used to prepare ZnO sol. ZnO and ZnAl₂O₄ coated aluminum borate whiskers were separately prepared by a sol–gel process. The results show that ZnO forms when ZnO xerogel is calcined at 500 °C and it does not undergo any phase transformation in the range of 500 and 1000 °C during calcinations. In ZnO xerogel coated aluminum borate whiskers system, a large amount of heat, gas and pores are produced during the heating process. When ZnO xerogel coated aluminum borate whiskers are calcined at 500 °C, ZnO can be uniformly coated on the surface of the whikers and the coated whiskers can be easily dispersed in distilled water through an ultrasonic vibration apparatus. During the calcination of ZnO coated whiskers at 1000 °C, ZnO reacts with the whiskers and ZnAl₂O₄ forms on the surface of aluminum borate whiskers.     

Synthesis and characterization of chromium and tungsten tetracarbonyl bound to the bridging ligand 2,3-bis(2-pyridyl)pyrazine (dpp)

The synthesis, electronic absorption, infrared and ¹³C NMR spectra, and electrochemistry of [Cr(CO)₄]dpp and [W(CO)₄]dpp (dpp = 2,3-bis(2-pyridyl)pyrazine) are reported. Electronic absorption spectra in different solvents show solvatochromic behavior and indicate the metal to ligand charge transfer (MLCT) excited state is lower in energy than the ligand field (LF) excited state. Electrochemical results show the [Cr(CO)₄]dpp complex undergoes semi-reversible one electron oxidation, while [W(CO)₄]dpp undergoes irreversible one electron oxidation. ¹³C NMR spectra of both complexes show all carbons in the metal-bound dpp ring shift downfield. The amount of downfield shift for the series [M(CO)₄]dpp (M = Cr, Mo, W) is interpreted as indicating better M dπ → dpp pπ backbonding occurs for Mo and W than for Cr.     

Effects of aging time on V2O5 sol-gel coatings

Vanadium pentoxide (V₂O₅) sols have been used in conductive coatings and related applications [1, 2, 3]; however, the changes which may occur in the properties of these coatings with sols of different ages have not been carefully shown. Properties which may be dependent on the age of the sol (sol viscosity, film morphology and conductance) were measured in this work. The coating sols were prepared by ion-exchange of sodium metavanadate solutions.It was found that the coating thickness, sol viscosity, and surface morphology of the coatings were directly related to the age of the sol used. The dried coating thickness increased from 3 microns to 20 microns over a 30 day period. The sol viscosity increased from 1 centipoise to near 2 centipoise. The surface morphology of the coatings changed from that of a featureless surface at day 1 to a continual coverage of micron-sized fibers as the coating sols aged. The conductivity of the coatings, though, was unaffected by the age of the sol. The coating properties were correlated to the amount of polymerization of dissolved precursors in solution.     

Synthesis, structures and properties of new hybrid solids containing ruthenium complexes and polyoxometalates

Two new organic-inorganic hybrid solids containing Keggin ions and ruthenium complexes have been synthesized and characterized by FT-IR, UV-vis, luminescence, X-ray, and TG analysis. In KNa[Ru(bpy)₃]₂[H₂W₁₂O₄₀]·8H₂O (1), the [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine) complex ions are located in between the infinite one-dimensional double-chains formed by adjacent Keggin anions [H₂W₁₂O₄₀]⁶⁻ linked through {KO₇} and {NaO₆} polyhedra, while in K₆[Ru(pzc)₃]₂[SiW₁₂O₄₀]•12H₂O (2), the [Ru(pzc)₃]⁻ (pzc=pyrazine-2-carboxylate) complex anions are confined by layered networks of the [SiW₁₂O₄₀]⁴⁻ clusters connected by potassium ions. Both compounds exhibit three-dimensional frameworks through noncovalent interactions such as hydrogen bonds and anion?π interactions. Additionally, compound 1 shows strong luminescence at 604 nm in solid state at room temperature.     

Reactions of dichlorobis(ditertiaryphosphine)-ruthenium(II) with carbon monoxide: Preparation of dicarbonylbis(ditertiaryphosphine) ruthenium(II) cations

Reactions of RuCl₂(L-L)₂ (L-L = dppm or dppe) with CO and silver salts of non coordinating anions produce [Ru(CO)₂(L-L)₂]X₂ which, once formed, are stable to CO loss. However, the fluxional five coordinate intermediates [Ru(Cl) (L-L)₂]X, which in some cases may contain ion pairs, are sufficiently electrophilic to abstract fluoride ion from [BF₄]^? or to coordinate other ions in solution such as [O₂PF₂]^? formed by hydrolysis of [PF₆]^?. A series of complexes of general formula [Ru(CO)₂ (dppm)₂AgY]X₂ may also be isolated and are shown to contain a dppm ligand bridging ruthenium and silver, the bond between which is reversibly cleaved by nitromethane on the nmr timescale.     

Synthesis of transparent mixed vanadia/niobia gels and their decomposition to a new metastable VNb9O25 phase

Controlled hydrolysis and condensation of a mixture of vanadyl-tris-n-propoxide, VO(OPr)₃, and niobium pentaethoxide, [Nb(OEt)₅]₂, at 5 °C in propanol yields clear and transparent gels in which the ratio of V:Nb is 1:1, 1:4.5 or 1:9. Oxalic acid and low temperatures are used to slow down the rate of condensation processes. At 800 °C, the thermal decomposition of a gel with the composition 1:9 forms a thermodynamically metastable, new phase of the composition VNb₉O₂₅. At lower temperatures, metastable solid solutions with TT-Nb₂O₅ structure (600 °C) and M-Nb₂O₅ structure (700 °C) are formed from the amorphous xerogel. The new VNb₉O₂₅ phase is structurally related to M-Nb₂O₅. The solid solution with M-Nb₂O₅ structure acts structure directing, leading preferentially to a monoclinic low-temperature form of VNb₉O₂₅. The full transformation of this metastable phase to the well known tetragonal VNb₉O₂₅ requires a annealing temperature of about 1000 °C.     

Synthesis and properties of ruthenium(II) complexes of 3,3′-polymethylene-2-(pyrid-2′-yl)benzo[b]-1,10-phenanthrolines

Coordination abilities of unsymmetrical tridentate ligands, 3,3′-polymethylene-2-(pyrid-2′-yl)-benzo[b]-1,10-phenanthrolines (4) were studied. Reactions of the 3,3′-di- and 3,3′-trimethylene-2-(pyrid-2′-yl)benzo[b]-1,10-phenanthrolines (4b and 4c) with RuCl₃ ? 3H₂O afforded [Ru(4b)₂]²⁺ and [Ru(4c)₂]²⁺ in 57% and 78% yield, respectively, while reactions of the parent non-bridged ligand (4a), tetramethylene-bridged ligand (4d), and fully aromatized ligand (4e) afforded a messy mixture. Reactions of 4 with Ru(tpy)Cl₃ (tpy = 2,2′;6′,2″-terpyridine) afforded [Ru(tpy)(4)]²⁺ in 61–72% yields. UV absorption spectra of the ligands showed four ligand-centered (LC) π–π* transitions and their Ru complexes showed four LC π–π* transitions and one Ru(d_π) → ligand(π*) MLCT. The ligands showed three major emission maxima (λ _emission) in the region of 393–418, 416–445, and 437–471 nm in which λ _emission is highly dependent on the length of the methylene bridge connecting C3 of benzo[b]-1,10-phenanthroline and C3 of pyridine. Ru complexes with fully aromatic ligand, [Ru(tpy)(4e)]²⁺, and the most distorted ligand, [Ru(tpy)(4d)]²⁺, showed two emission maxima at 410 and 444–446 nm, while the others showed one emission at 410 nm. Each of the emission maxima is bathochromatically shifted from the complex with the most distorted ligand (4d) to the complex with fully aromatized planar ligand (4e) indicating lower energy emission.     

Photophysical and Photochemical Properties of Ru(bpy)3 2+ in Si-Ti Mixed Oxides Xerogels Prepared by the Sol-Gel Process

The luminescence spectra and lifetime of tris(2,2-bipyridine)ruthenium(II), Ru(bpy)₃ ²⁺, were studied in sol-gel reaction systems of tetramethoxysilane (TMOS) and titanium(IV) isopropoxide (TTIP) with HCl. Luminescence lifetime in the TMOS system increased as the sol-gel reaction proceeded, because diffusion-controlled luminescence quenching such as oxygen and collisional quenching with solvent molecules were suppressed in the rigid matrices. On the other hand, luminescence lifetime in the TTIP system decreased during the sol-gel reaction. The decrease in lifetime was ascribed to electron transfer from photoexcited Ru(bpy)₃ ²⁺ to the conduction band of the TiO₂ xerogels. Extended X-ray absorption fine structure (EXAFS) measurements were done to associate lifetime in the Si-Ti xerogels with the structures of Ti⁴⁺ sites in the xerogels.     

Development of mullite and mullite/Al2O3 precursor sols for electrophoretic deposition of oxidation protection coatings

Mullite and mullite/Al₂O₃ precursor sols have been developed for the deposition of oxidation barrier coatings on carbon fibre reinforced composites using a combination of sol–gel synthesis and electrophoresis.The sols were synthesised by controlled hydrolysis and condensation of TEOS (tetraethoxysilane) and Al(OBu^s)₃ (aluminium tri-sec-butylate). The main objective was the definition of synthesis conditions which yield sols suitable for the electrophoretic deposition (EPD). Measurements of the Electrokinetic Sonic Amplitude were used to investigate the electrokinetic properties of the sols in the as-prepared state and depending on the later addition of H₂O. ²⁹Si CP/MAS NMR spectra of dried precursor samples were recorded to study the homogeneity of Al/Si mixture. The progress of crystallisation with increasing temperature of heat treatment was examined by XRD. Oxidation protection coatings on C/C–SiC composites were prepared by EPD.Whereas a low H₂O to TEOS ratio during the sol synthesis was advantageous for a low mullite formation temperature, a high H₂O to TEOS ratio was necessary to enable the EPD. The synthesis of a sol with a low H₂O to TEOS ratio in the first step and the later modification of this sol by the addition of water was a successful method to combine the required electrokinetic properties and mullitisation temperatures below 1200 °C.     

Influence of a chelating agent on optical and morphological properties of YAG: Tb3+ phosphors prepared by the sol-gel process

Chemical modifications are widely used in sol-gel method in order to control the mechanisms involved during hydrolysis-condensation and polymerization processes. In this paper, the influence of acetylaceton (acac) used as a chelating agent in the synthesis of undoped and Tb³⁺-doped Y₃Al₅O₁₂ (YAG) powders and sols, has been investigated. Its effects on samples crystallization and morphology have been studied by means of high-temperature X-ray diffraction (HTXRD), thermal analysis (DTA-TG), infrared (IR) and Raman spectroscopies, transmission electron microscopy (TEM) and laser granulometry. It was shown that acetylaceton enhances the structural organization of YAG compound. Moreover, acac-modified powders exhibit much smaller particles than unmodified ones. Optical study has also been achieved on doped samples. Laser induced luminescence spectra and fluorescence decays of Tb³⁺ ions show that acac affects the optical properties of YAG: Tb³⁺ for any types of samples (sol, xerogel or crystallized powder). Powders demonstrate a better luminescence yield without acetylaceton, whereas stabilized sols are more efficient than unstabilized ones.     

Increased Water Reduction Efficiency of Polyelectrolyte‐Bound Trimetallic [Ru,Rh,Ru] Photocatalysts in Air‐Saturated Aqueous Solutions

The groundbreaking use of polyelectrolytes to increase the efficiency of supramolecular photocatalysts in solar H₂ production schemes under aqueous aerobic conditions is reported. Supramolecular photocatalysts of the architecture [{(TL)₂Ru(BL)}₂RhX₂]⁵⁺ (BL=bridging ligand, TL=terminal ligand, X=halide) demonstrate high efficiencies in deoxygenated organic solvents but do not function in air‐saturated aqueous solution because of the quenching of the metal‐to‐ligand charge‐transfer (MLCT) excited state under these conditions. The new photocatalytic system incorporates poly(4‐styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)₂Ru(dpp)}₂RhCl₂]⁵⁺ (bpy=2,2′‐bipyridine, dpp=2,3‐bis(2‐pyridyl)pyrazine). PSS has a profound impact on the photocatalyst efficiency, increasing H₂ production over three times that of deoxygenated aqueous solutions alone. H₂ photocatalysis proceeds even under aerobic conditions for PSS‐containing solutions, an exciting consequence for solar hydrogen‐production research.