Charge‐Neutral Amidinate‐Containing Iridium Complexes Capable of Efficient Photocatalytic Water Reduction

Two new charge‐neutral iridium complexes, [Ir(tfm‐ppy)₂(N,N′‐diisopropyl‐benzamidinate)] ( 1 ) and [Ir(tfm‐ppy)₂(N,N′‐diisopropyl‐4‐diethylamino‐3,5‐dimethyl‐benzamidinate)] ( 2 ) (tfm‐ppy=4‐trifluoromethyl‐2‐phenylpyridine) containing an amidinate ligand and two phenylpyridine ligands were designed and characterised. The photophysical properties, electrochemical behaviours and emission quenching properties of these species were investigated. In concert with the cobalt catalyst [Co(bpy)₃]²⁺, members of this new class of iridium complexes enable the photocatalytic generation of hydrogen from mixed aqueous solutions via an oxidative quenching pathway and display long‐term photostability under constant illumination over 72 h; one of these species achieved a relatively high turnover number of 1880 during this time period. In the case of complex 1 , the three‐component homogeneous photocatalytic system proved to be more efficient than a related system containing a charged complex, [Ir(tfm‐ppy)₂(dtb‐bpy)]⁺ ( 3 , dtb‐bpy=4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl). In combination with a rhodium complex as a water reduction catalyst, the performances of the systems using both complexes were also evaluated, and these systems exhibited a more efficient catalytic propensity for water splitting than did the cobalt‐based systems that have been studied previously.     

Enhanced Electrochemiluminescence from a Stoichiometric Ruthenium(II)–Iridium(III) Complex Soft Salt

Electrochemiluminescence (ECL) and electrochemistry are reported for a heterometallic soft salt, [Ru(dtbubpy)₃][Ir(ppy)₂(CN)₂]₂ ( [Ir][Ru][Ir] ), consisting of a 2:1 ratio of complementary charged Ru and Ir complexes possessing two different emission colors. The [Ru]²⁺ and [Ir]^? moieties in the [Ir][Ru][Ir] greatly reduce the energy required to produce ECL. Though ECL intensity in the annihilation path was enhanced 18× relative to that of [Ru(bpy)₃]²⁺, ECL in the co‐reactant path with tri‐n‐propylamine was enhanced a further 4×. Spooling spectroscopy gives insight into ECL mechanisms: the unique light emission at 634 nm is due to the [Ru]²⁺* excited state and no [Ir]^?* was generated in either route. Overall, the soft salt system is anticipated to be attractive and suitable for the development of efficient and low‐energy‐cost ECL detection systems.     

Blue Electrogenerated Chemiluminescence from Water‐Soluble Iridium Complexes Containing Sulfonated Phenylpyridine or Tetraethylene Glycol Derivatized Triazolylpyridine Ligands

Incorporating phenylpyridine‐ and triazolylpyridine‐based ligands decorated with methylsulfonate or tetraethylene glycol (TEG) groups, a series of iridium(III) complexes has been created for green and blue electrogenerated chemiluminescence under analytically useful aqueous conditions, with tri‐n‐propylamine as a coreactant. The relative electrochemiluminescence (ECL) intensities of the complexes were dependent on the sensitivity of the photodetector over the wavelength range and the pulse time of the applied electrochemical potential. In terms of the integrated area of corrected ECL spectra, with a pulse time of 0.5 s, the intensities of the Ir^III complexes were between 18 and 102 % that of [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine). However, when the intensities were measured with a typical bialkali photomultiplier tube, the signal of the most effective blue emitter, [Ir(df‐ppy)₂(pt‐TEG)]⁺ (df‐ppy=2‐(2,4‐difluorophenyl)pyridine anion, pt‐TEG=1‐(2‐(2‐(2‐(2‐hydroxyethoxy)ethoxy)ethoxy)ethyl)‐4‐(2‐pyridyl)‐1,2,3‐triazole), was over 1200 % that of the orange–red emitter [Ru(bpy)₃]²⁺. A combined experimental and theoretical investigation of the electrochemical and spectroscopic properties of the Ir^III complexes indicated that the greater intensity from [Ir(df‐ppy)₂(pt‐TEG)]⁺ relative to those of the other Ir^III complexes resulted from a combination of many factors, rather than being significantly favored in one area.     

Amine‐Rich Nitrogen‐Doped Carbon Nanodots as a Platform for Self‐Enhancing Electrochemiluminescence

Amine‐rich nitrogen‐doped carbon nanodots (NCNDs) have been successfully used as co‐reactant in electrochemiluminescence (ECL) processes. Primary or tertiary amino groups on NCNDs have been studied as co‐reactant sites for Ru(bpy)₃²⁺ ECL, showing their eligibility as powerful alternatives to tripropylamine (TPrA). We also report the synthesis and ECL behavior of a new covalently linked hybrid of NCNDs and Ru(bpy)₃²⁺. Notably, the NCNDs in the hybrid act both as carrier for ECL labels and as co‐reactant for ECL generation. As a result, the hybrid shows a higher ECL emission as compared to the combination of the individual components, suggesting the self‐enhancing ECL of the ruthenium complex due to an intramolecular electron transfer process.     

Nanoscale Metal–Organic Layers for Deeply Penetrating X‐ray‐Induced Photodynamic Therapy

We report the rational design of metal–organic layers (MOLs) that are built from [Hf₆O₄(OH)₄(HCO₂)₆] secondary building units (SBUs) and Ir[bpy(ppy)₂]⁺‐ or [Ru(bpy)₃]²⁺‐derived tricarboxylate ligands (Hf‐BPY‐Ir or Hf‐BPY‐Ru; bpy=2,2′‐bipyridine, ppy=2‐phenylpyridine) and their applications in X‐ray‐induced photodynamic therapy (X‐PDT) of colon cancer. Heavy Hf atoms in the SBUs efficiently absorb X‐rays and transfer energy to Ir[bpy(ppy)₂]⁺ or [Ru(bpy)₃]²⁺ moieties to induce PDT by generating reactive oxygen species (ROS). The ability of X‐rays to penetrate deeply into tissue and efficient ROS diffusion through ultrathin 2D MOLs (ca. 1.2 nm) enable highly effective X‐PDT to afford superb anticancer efficacy.     

Understanding Electrogenerated Chemiluminescence Efficiency in Blue‐Shifted Iridium(III)‐Complexes: An Experimental and Theoretical Study

Compared to tris(2‐phenylpyridine)iridium(III) ([Ir(ppy)₃]), iridium(III) complexes containing difluorophenylpyridine (df‐ppy) and/or an ancillary triazolylpyridine ligand [3‐phenyl‐1,2,4‐triazol‐5‐ylpyridinato (ptp) or 1‐benzyl‐1,2,3‐triazol‐4‐ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25–60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with [Ir(ppy)₃] and [Ir(df‐ppy)₃], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence (ECL) intensities (using tri‐n‐propylamine (TPA) as a co‐reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M⁺) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M⁺ LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency. The theoretical and experimental data together show that the best strategy for the design of efficient new blue‐shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, [Ir(df‐ppy)₂(ptb)]⁺ was most attractive as a blue‐emitter for ECL detection, featuring a large hypsochromic shift (λ_max=454 and 484 nm), superior co‐reactant ECL intensity than the archetypal homoleptic green and blue emitters: [Ir(ppy)₃] and [Ir(df‐ppy)₃] (by over 16‐fold and threefold, respectively), and greater solubility in polar solvents.     

Electrochemiluminescence of Tris(2,2′‐bipyridine)ruthenium with Various Co‐reactants under Ultrasound Irradiation

Electrochemiluminescence (ECL) of tris(2,2′‐bipyridine)ruthenium, Ru(bpy)₃²⁺ in the presence of various co‐reactants, such as tripropylamine (TPA), oxalate ion (C₂O₄^2?), ascorbic acid (H₂A) and dehydroascorbic acid (DHA), were investigated under ultrasound irradiation. In sono‐ECL experiments, an indium‐thin‐oxide (ITO) was used as working electrode, and a titanium tipped sonic horn probe (diameter 2 mm) which operated at a frequency of 20 kHz was set in the front of the ITO electrode. Under the ultrasound irradiation, ECL signals were found to be significantly enhanced when TPA and C₂O₄^2? were used as co‐reactants, only slightly enhanced in Ru(bpy)₃²⁺/DHA system, but total quenched in Ru(bpy)₃²⁺/H₂A system. The difference of Ru(bpy)₃²⁺ ECL behaviors for various co‐reactant could to be due to the different kinetics of catalytic reactions associated in ECL schemes. ECL quenching effect observed in Ru(bpy)₃²⁺/H₂A system was suggested to be due to electron transfer (ET) route between the excited state *Ru(bpy)₃²⁺ and ascorbate anion HA^? diffused from the bulk solution, where the diffusional HA^? species served as electron donor. The effect becomes more pronounced upon sonication because the effective collision frequency between *Ru(bpy)₃²⁺ and HA^? would be significantly increased by the enhanced mass transport effect of ultrasound.     

Electronic Coupling between Two Amine Redox Sites through the 5,5′‐Positions of Metal‐Chelating 2,2′‐Bipyridines

Electron delocalization of new mixed‐valent (MV) systems with the aid of lateral metal chelation is reported. 2,2′‐Bipyridine (bpy) derivatives with one or two appended di‐p‐anisylamino groups on the 5,5′‐positions and a coordinated [Ru(bpy)₂] (bpy=2,2′‐bipyridine), [Re(CO)₃Cl], or [Ir(ppy)₂] (ppy=2‐phenylpyridine) component were prepared. The single‐crystal molecular structure of the bis‐amine ligand without metal chelation is presented. The electronic properties of these complexes were studied and compared by electrochemical and spectroscopic techniques and DFT/TDDFT calculations. Compounds with two di‐p‐anisylamino groups were oxidized by a chemical or electrochemical method and monitored by near‐infrared (NIR) absorption spectral changes. Marcus–Hush analysis of the resulting intervalence charge‐transfer transitions indicated that electron coupling of these mixed‐valent systems is enhanced by metal chelation and that the iridium complex has the largest coupling. TDDFT calculations were employed to interpret the NIR transitions of these MV systems.     

IrIII and RuII Complexes Containing Triazole‐Pyridine Ligands: Luminescence Enhancement upon Substitution with β‐Cyclodextrin

Novel 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine (pytl) ligands have been prepared by “click chemistry” and used in the preparation of heteroleptic complexes of Ru and Ir with bipyridine (bpy) and phenylpyridine (ppy) ligands, respectively, resulting in [Ru(bpy)₂(pytl‐R)]Cl₂ and [Ir(ppy)₂(pytl‐R)]Cl (R=methyl, adamantane (ada), β‐cyclodextrin (βCD)). The two diastereoisomers of the Ir complex with the appended β‐cyclodextrin, [Ir(ppy)₂(pytl‐βCD)]Cl, were separated. The [Ru(bpy)₂(pytl‐R)]Cl₂ (R=Me, ada or βCD) complexes have lower lifetimes and quantum yields than other polypyridine complexes. In contrast, the cyclometalated Ir complexes display rather long lifetimes and very high emission quantum yields. The emission quantum yield and lifetime (Φ=0.23, τ=1000 ns) of [Ir(ppy)₂(pytl‐ada)]Cl are surprisingly enhanced in [Ir(ppy)₂(pytl‐βCD)]Cl (Φ=0.54, τ=2800 ns). This behavior is unprecedented for a metal complex and is most likely due to its increased rigidity and protection from water molecules as well as from dioxygen quenching, because of the hydrophobic cavity of the βCD covalently attached to pytl. The emissive excited state is localized on these cyclometalating ligands, as underlined by the shift to the blue (450 nm) upon substitution with two electron‐withdrawing fluorine substituents on the phenyl unit. The significant differences between the quantum yields of the two separate diastereoisomers of [Ir(ppy)₂(pytl‐βCD)]Cl (0.49 vs. 0.70) are attributed to different interactions of the chiral cyclodextrin substituent with the Δ and Λ isomers of the metal complex.     

Electrochemiluminescence Biosensor Based on PEDOT‐PSS‐ Graphene Functionalized ITO Electrode

A novel and sensitive electrochemiluminescence (ECL) method for ethanol biosensor was developed by co‐immobilizing the enzyme and ECL reagent Ru(bpy)₃²⁺ on the poly‐(3,4‐ethylene dioxythiophene) and polystyrene sulfonate functionalized graphene (PEDOT‐PSS‐G) nanocomposite film. Positively charged Ru(bpy)₃²⁺ could be immobilized effectively on the electrode surface with the negatively charged PSS and graphene, which provided a stable ECL platform for further modification with the enzyme. Moreover, the introduction of PEDOT and graphene can be acted as a conducting pathway to accelerate the electron transfer due to the high conductivity. Such biosensor combined enzymatic selectivity with the amplification of PEDOT‐PSS‐G performed well with a wide linear range, high sensitivity and good stability. The sensing platform was successfully applied to determine the amounts of alcohol in real samples.     

Electrochemiluminescence Studies of Phosphorescent Dopant and Host Molecules of Polymer Light-emitting Diodes

Electrochemiluminescence (ECL) from tris(2‐phenylpyridine)irdium [Ir(ppy)₃] was investigated following cross reaction of its anion with oxidized poly(N‐vinyl‐carbazole) (PVK) and its cation with reduced 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD). Both cross reactions show Ir(ppy)₃ emission and the cross reaction of PVK^+·/Ir(ppy)⁻₃ showed the highest ECL intensity. The comparisons of the reaction enthalpy and the energy of Ir(ppy)₃ light emitting shows that reaction between PVK^+· and Ir(ppy)⁻₃ is energy sufficient to populate metal‐to‐ligand charge transfer (MLCT) excited singlet (3.04 eV) of Ir(ppy)₃, while the reaction between Ir(ppy)⁺₃ and PBD^{− ·} is energy efficient to populate MLCT excited triplet (2.4 eV). The ECL result in solution reveals that the energy released from charge transfer between the Ir(ppy)₃ and PVK or PBD is sufficient to produce the excited state of Ir(ppy)₃ in solid polymer light‐emitting diodes (PLEDs) based on PVK:PBD hosts doped by Ir(ppy)₃. These results obtained will provide further insight into charge‐transfer excitation in PLEDs.     

Dual Intramolecular Electron Transfer for In Situ Coreactant‐Embedded Electrochemiluminescence Microimaging of Membrane Protein

The demand for transporting coreactant to emitter and short lifetime of the radicals in electrochemiluminescence (ECL) emission inhibit greatly its application in cytosensing and microscopic imaging. Herein we designed a dual intramolecular electron transfer strategy and tertiary amine conjugated polymer dots (TEA‐Pdots) to develop a coreactant‐embedded ECL mechanism and microimaging system. The TEA‐Pdots could produce ECL emission at +1.2 V without need of coreactant in test solution. The superstructure and intramolecular electron transfer led to unprecedented ECL strength, which was 132 and 45 times stronger than those from the mixture of Pdots with TEA at equivalent and 62.5 times higher amounts, respectively. The ECL efficiency was even higher than that of typical [Ru(bpy)₃]²⁺ system. Therefore, this strategy and coreactant‐embedded ECL system could be used for in situ ECL microimaging of membrane protein on single living cells without additional permeable treatment for transporting coreactant. The feasibility and validity were demonstrated by evaluating the specific protein expression on cell surface. This work opens new avenues for ECL applications in single cell analysis and dynamic study of biological events.     

Formation of [Ru(bpy)3]2+‐Containing Microstructures Induced by Electrostatic Assembly and Their Application in Solid‐State Detection of Electrochemiluminescence

Tris(2,2′‐bipyridine)ruthenium(II) ([Ru(bpy)₃]²⁺) is one of the most extensively studied and used electrochemiluminescent (ECL) compounds owing to its superior properties, which include high sensitivity and stability under moderate conditions in aqueous solution. In this paper we present a simple method for the preparation of [Ru(bpy)₃]²⁺‐containing microstructures based on electrostatic assembly. The formation of such microstructures occurs in a single process by direct mixing of aqueous solutions of [Ru(bpy)₃]Cl₂ and K₃[Fe(CN)₆] at room temperature. The electrostatic interactions between [Ru(bpy)₃]²⁺ cations and [Fe(CN)₆]^3? anions cause them to assemble into the resulting microstructures. Both the molar ratio and concentration of reactants were found to have strong influences on the formation of these microstructures. Most importantly, the resulting [Ru(bpy)₃]²⁺‐containing microstructures exhibit excellent ECL behavior and, therefore, hold great promise for solid‐state ECL detection in capillary electrophoresis (CE) or CE microchips.     

Long‐Lived Room‐Temperature Deep‐Red‐Emissive Intraligand Triplet Excited State of Naphthalimide in Cyclometalated IrIII Complexes and its Application in Triplet‐Triplet Annihilation‐Based Upconversion

Cyclometalated Ir^III complexes with acetylide ppy and bpy ligands were prepared (ppy=2‐phenylpyridine, bpy=2,2′‐bipyridine) in which naphthal ( Ir‐2 ) and naphthalimide (NI) were attached onto the ppy ( Ir‐3 ) and bpy ligands ( Ir‐4 ) through acetylide bonds. [Ir(ppy)₃] ( Ir‐1 ) was also prepared as a model complex. Room‐temperature phosphorescence was observed for the complexes; both neutral and cationic complexes Ir‐3 and Ir‐4 showed strong absorption in the visible range (ε=39600 M ^?1 cm^?1 at 402 nm and ε=25100 M ^?1 cm^?1 at 404 nm, respectively), long‐lived triplet excited states (τ_T=9.30 μs and 16.45 μs) and room‐temperature red emission (λ_em=640 nm, Φ_p=1.4 % and λ_em=627 nm, Φ_p=0.3 %; cf. Ir‐1 : ε=16600 M ^?1 cm^?1 at 382 nm, τ_em=1.16 μs, Φ_p=72.6 %). Ir‐3 was strongly phosphorescent in non‐polar solvent (i.e., toluene), but the emission was completely quenched in polar solvents (MeCN). Ir‐4 gave an opposite response to the solvent polarity, that is, stronger phosphorescence in polar solvents than in non‐polar solvents. Emission of Ir‐1 and Ir‐2 was not solvent‐polarity‐dependent. The T₁ excited states of Ir‐2 , Ir‐3 , and Ir‐4 were identified as mainly intraligand triplet excited states (³IL) by their small thermally induced Stokes shifts (ΔE_s), nanosecond time‐resolved transient difference absorption spectroscopy, and spin‐density analysis. The complexes were used as triplet photosensitizers for triplet‐triplet annihilation (TTA) upconversion and quantum yields of 7.1 % and 14.4 % were observed for Ir‐2 and Ir‐3 , respectively, whereas the upconversion was negligible for Ir‐1 and Ir‐4 . These results will be useful for designing visible‐light‐harvesting transition‐metal complexes and for their applications as triplet photosensitizers for photocatalysis, photovoltaics, TTA upconversion, etc.     

Two‐Photon Chemistry in Ruthenium 2,2′‐Bipyridyl‐Functionalized Single‐Wall Carbon Nanotubes

Ruthenium polypyridyl complexes are widely used as light harvesters in dye‐sensitized solar cells. Since one of the potential applications of single‐wall carbon nanotubes (SWCNTs) and their derived materials is their use as active components in organic and hybrid solar cells, the study of the photochemistry of SWCNTs with tethered ruthenium polypyridyl complexes is important. A water‐soluble ruthenium tris(bipyridyl) complex linked through peptidic bonds to SWCNTs (Ru‐SWCNTs) was prepared by radical addition of thiol‐terminated SWCNT to a terminal C?C double bond of a bipyridyl ligand of the ruthenium tris(bipyridyl) complex. The resulting macromolecular Ru‐SWCNT (≈500 nm, 15.6 % ruthenium complex content) was water‐soluble and was characterized by using TEM, thermogravimetric analysis, chemical analysis, and optical spectroscopy. The emission of Ru‐SWCNT is 1.6 times weaker than that of a mixture of [Ru(bpy)₃]²⁺ and SWCNT of similar concentration. Time‐resolved absorption optical spectroscopy allows the detection of the [Ru(bpy)₃]²⁺‐excited triplet and [Ru(bpy)₃]⁺. The laser flash studies reveal that Ru‐SWCNT exhibits an unprecedented two‐photon process that is enabled by the semiconducting properties of the SWCNT. Thus, the effect of the excitation wavelength and laser power on the transient spectra indicate that upon excitation of two [Ru(bpy)₃]²⁺ complexes of Ru‐SWCNT, a disproportionation process occurs leading to delayed formation of [Ru(bpy)₃]⁺ and the performance of the SWCNT as a semiconductor. This two‐photon delayed [Ru(bpy)₃]⁺ generation is not observed in the photolysis of [Ru(bpy)₃]³⁺; SWCNT acts as an electron wire or electron relay in the disproportionation of two [Ru(bpy)₃]²⁺ triplets in a process that illustrates that the SWCNT plays a key role in the process. We propose a mechanism for this two‐photon disproportionation compatible with i) the need for high laser flux, ii) the long lifetime of the [Ru(bpy)₃]²⁺ triplets, iii) the semiconducting properties of the SWNT, and iv) the energy of the HOMO/LUMO levels involved.     

An Unusually Delocalized Mixed‐Valence State of a Cyanidometal‐Bridged Compound Induced by Thermal Electron Transfer

The heterometallic complexes trans ‐[Cp(dppe)FeNCRu(o ‐bpy)CNFe(dppe)Cp][PF₆]_n ( 1 [PF₆]_n , n =2, 3, 4; o ‐bpy=1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane, dppe=1,2‐bis(diphenylphosphino)ethane, Cp=1,3‐cyclopentadiene) in three distinct states have been synthesized and fully characterized. 1 ³⁺[PF₆]₃ and 1 ⁴⁺[PF₆]₄ are the one‐ and two‐electron oxidation products of 1 ²⁺[PF₆]₂, respectively. The investigated results suggest that 1 [PF₆]₃ is a Class II mixed valence compound. 1 [PF₆]₄ after a thermal treatment at 400 K shows an unusually delocalized mixed valence state of [Fe^III‐NC‐Ru^III‐CN‐Fe^II], which is induced by electron transfer from the central Ru^II to the terminal Fe^III in 1 [PF₆]₄, which was confirmed by IR spectroscopy, magnetic data, and EPR and Mössbauer spectroscopy.     

The Fundamentals of Real‐Time Surface Plasmon Resonance/Electrogenerated Chemiluminescence

We report the integration of surface plasmon resonance (SPR), cyclic voltammetry and electrochemiluminescence (ECL) responses to survey the interfacial adsorption and energy transfer processes involved in ECL on a plasmonic substrate. It was observed that a Tween 80/tripropylamine nonionic layer formed on the gold electrode of the SPR sensor, while enhancing the ECL emission process, affects the electron transfer process to the luminophore, Ru(bpy)₃²⁺, which in turn has an impact on the plasmon resonance. Concomitantly, the surface plasmon modulated the ECL intensity, which decreased by about 40 %, due to an interaction between the excited state of Ru(bpy)₃²⁺ and the plasmon. This occurred only when the plasmon was excited, demonstrating that the optically excited surface plasmon leads to lower plasmon‐mediated luminescence and that the plasmon interacts with the excited state of Ru(bpy)₃²⁺ within a very thin layer.     

Effect of External Pressure on the Excitation Energy Transfer from [Cr(ox)3]3− to [Cr(bpy)3]3+ in [Rh1−xCrx(bpy)3][NaM1−yCry(ox)3]ClO4

Resonant excitation energy transfer from [Cr(ox)₃]^3? to [Cr(bpy)₃]³⁺ in the doped 3D oxalate networks [Rh_1?xCr_x(bpy)₃][NaM^III_1?yCr_y(ox)₃]ClO₄ (ox=C₂O₄^?, bpy=2,2′‐bipyridine, M=Al, Rh) is due to two types of interaction, namely super exchange coupling and electric dipole–dipole interaction. The energy transfer probability for both mechanisms is proportional to the spectral overlap of the ²E→⁴A₂ emission of the [Cr(ox)₃]^3? donor and the ⁴A₂→²T₁ absorption of the [Cr(bpy)₃]³⁺ acceptor. The spin‐flip transitions of (pseudo‐)octahedral Cr³⁺ are known to shift to lower energy with increasing pressure. Because the shift rates of the two transitions in question differ, the spectral overlap between the donor emission and the acceptor absorption is a function of applied pressure. For [Rh_1?xCr_x(bpy)₃][NaM_1?yCr_y(ox)₃]ClO₄ the spectral overlap is thus substantially reduced on increasing pressure from 0 to 2.5 GPa. As a result, the energy transfer probability decreases with increasing pressure as evidenced by a decrease in the relative emission intensity from the [Cr(bpy)₃]³⁺ acceptor.     

Tricyclometalated Iridium Complexes as Highly Stable Photosensitizers for Light‐Induced Hydrogen Evolution

The development of an efficient and stable artificial photosensitizer for visible‐light‐driven hydrogen production is highly desirable. Herein, a new series of charge‐neutral, heteroleptic tricyclometalated iridium(III) complexes, [Ir(thpy)₂(bt)] ( 1 – 4 ; thpy=2,2′‐thienylpyridine, bt=2‐phenylbenzothiazole and its derivatives), were systematically synthesized and their structural, photophysical, and electrochemical properties were established. Three solid‐state structures were studied by X‐ray crystallographic analysis. This design offers the unique opportunity to drive the metal‐to‐ligand charge‐transfer (MLCT) band to longer wavelengths for these iridium complexes. We describe new molecular platforms that are based on these neutral iridium complexes for the production of hydrogen through visible‐light‐induced photocatalysis over an extended period of time in the presence of [Co(bpy)₃]²⁺ and triethanolamine (TEOA). The maximum amount of hydrogen was obtained under constant irradiation over 72 h and the system could regenerate its activity upon the addition of cobalt‐based catalysts when hydrogen evolution ceased. Our results demonstrated that the dissociation of the [Co(bpy)₃]²⁺ catalyst contributed to the loss of catalytic activity and limited the long‐term catalytic performance of the systems. The properties of the neutral complexes are compared in detail to those of two known non‐neutral bpy‐type complexes, [Ir(thpy)₂(dtb‐bpy)]⁺ ( 5 ) and [Ir(ppy)₂(dtb‐bpy)]⁺ ( 6 ; ppy=2‐phenylpyridine, dtb‐bpy=4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl). This work is expected to contribute toward the development of long‐lasting solar hydrogen‐production systems.     

Trifluoromethylchlorosulfonylation of Alkenes: Evidence for an Inner‐Sphere Mechanism by a Copper Phenanthroline Photoredox Catalyst

A visible‐light‐mediated procedure for the unprecedented trifluoromethylchlorosulfonylation of unactivated alkenes is presented. It uses [Cu(dap)₂]Cl as catalyst, and contrasts with [Ru(bpy)₃]Cl₂, [Ir(ppy)₂(dtbbpy)]PF₆, or eosin Y that exclusively give rise to trifluoromethylchlorination of the same alkenes. It is assumed that [Cu(dap)₂]Cl plays a dual role, that is, acting both as an electron transfer reagent as well as coordinating the reactants in the bond forming processes.