Photocatalytic Hydrogen Production Using a Red-Absorbing Ir(III)–Co(III) Dyad

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Efficient Red-Light-Driven Hydrogen Evolution with an Anthraquinone Organic Dye

The direct utilization of the full solar spectrum to obtain renewable fuels remains a challenge because the conversion of the low-energy light (red and near-infrared) is difficult. Current light-driven systems show activity for hydrogen generation with the high-energy part of sunlight. Here we report the use of a simple anthraquinone organic dye in an artificial photosynthetic system that promotes efficient red-light-driven production of hydrogen. The system contains no noble metal and exhibits a turnover number greater than 0.78 million and a quantum yield of 30.6% at 630 nm. A mechanistic study revealed that the excited-state and redox properties of the chromophore are critical to achieving high activity and stability.

Accumulation of mono-reduced [Ir(piq)2(LL)] photosensitizers relevant for solar fuels production

A series of nine [Ir(piq)₂(LL)]⁺.PF₆^- photosensitizers, where piqH = 1-phenylisoquinoline, was developed and investigated for excited-state electron transfer with sacrificial electron donors that included triethanolamine (TEOA), triethylamine (TEA) and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) in acetonitrile. The photosensitizers were obtained in 57-82% yield starting from the common [Ir(piq)₂µ-Cl]₂ precursor and were all characterized by UV-Vis absorption as well as by steady-state, time-resolved spectroscopies and electrochemistry. The excited-state lifetimes ranged from 250 to 3350 ns and excited-state electron transfer quenching rate constants in the 10⁹ M^-1 s^-1 range were obtained when BIH was used as electron donor. These quenching rate constants were three orders of magnitude higher than when TEA or TEOA was used. Steady-state photolysis in the presence of BIH showed that the stable and reversible accumulation of mono-reduced photosensitizers was possible, highlighting the potential use of these Ir-based photosensitizers in photocatalytic reactions relevant for solar fuels production.

Red Absorbing Cyclometalated Ir(III) Diimine Photosensitizers Competent for Hydrogen Photocatalysis

Two new cyclometalated Ir(III) diimine complexes were used as photosensitizers for homogeneous hydrogen evolution reaction (HER). These complexes were characterized by electrochemistry, ultraviolet-visible absorption, time-resolved and steady-state photoluminescence spectroscopy as well as by theoretical methods. The metal-ligand-to-ligand charge transfer character of their lowest excited state was shown to be competent for efficient H₂ photoproduction in the presence of [Co(dmgH)₂(py)Cl] as the hydrogen evolution catalyst, triethanolamine as the sacrificial electron donor, and HBF₄ as the proton source. Under optimized experimental conditions, both complexes displayed HER over a period of more than 90 h, with turnover numbers reaching up to 11,650, 10,600, and 174 mol_H2 mol_PS^-1 under blue-, green-, and red-light irradiation, respectively. Both complexes showed higher stability and efficiency vs HER than most of the previously described systems of the same kind.

A cobalt mimochrome for photochemical hydrogen evolution from neutral water

A system for visible light-driven hydrogen production from water is reported. This system makes use of a synthetic mini-enzyme known as a mimochrome (CoMC6*a) consisting of a cobalt deuteroporphyrin and two attached peptides as a catalyst, [Ru(bpy)₃]²⁺ (bpy = 2,2'-bipyridine) as a photosensitizer, and ascorbic acid as a sacrificial electron donor. The system achieves turnover numbers (TONs) up to 10,000 with respect to catalyst and optimal activity at pH 7. Comparison with related systems shows that CoMC6*a maintains the advantages of biomolecular catalysts, while exceeding other cobalt porphyrins in terms of total TON and longevity of catalysis. Herein, we lay groundwork for future study, where the synthetic nature of CoMC6*a will provide a unique opportunity to tailor proton reduction chemistry and expand to new reactivity.

Photo-generation of H2 by Heterometallic Complexes

Multiple and different metals in a complex can accomplish single and sequential multi-step reactions, providing valuable procedures to obtain chemicals in one-pot synthetic routes. Biology has shown how cooperative catalysis...

Dinuclear 2,4-di(pyridin-2-yl)-pyrimidine based ruthenium photosensitizers for hydrogen photo-evolution under red light

In this study, we report two dinuclear Ru(II) complexes C1 and C2 and compare them to their mononuclear analogues Ref1 and Ref2. The dinuclear species exhibit a much stronger absorption, longer excited-state lifetimes and higher luminescence quantum yields than the mononuclear complexes. In addition, C1 and C2 are easier to reduce. An estimation of the driving forces for the electron transfer processes relevant to photocatalytic hydrogen evolution suggests that C1 and Ref2 possess similar activity as photosensitizer (PS). Yet, the improved photophysical properties of C1 make it a more promising candidate for hydrogen evolution. In hydrogen evolution experiments, C1 indeed exhibits increased activity as PS, however, the catalytic system loses its activity after only a few hours. C2 is less active than the mononuclear complexes despite its superior photophysical properties. This observation is attributed to a lack of driving force for the electron transfer towards the catalyst. Further studies of the dinuclear complex C1 show that it is indeed the PS, which decomposes under the catalytic conditions, presumably due to the electron transfer towards the catalyst being the rate-limiting step.

Cobaloxime Complex Salts: Synthesis, Patterning on Carbon Nanomembranes and Heterogeneous Hydrogen Evolution Studies

Cobaloximes are promising, earth‐abundant catalysts for the light‐driven hydrogen evolution reaction (HER). Typically, these cobalt(III) complexes are prepared in situ or employed in their neutral form, for example, [Co(dmgH)₂(py)Cl], even though related complex salts have been reported previously and could, in principle, offer improved catalytic activity as well as more efficient immobilization on solid support. Herein, we report an interdisciplinary investigation into complex salts [Co(dmgH)₂(py)₂]⁺[Co(dmgBPh₂)₂Cl₂]⁻, TBA+[Co(dmgBPh2)2Cl2]- and [Co(dmgH)₂(py)₂]⁺BArF⁻. We describe their strategic syntheses from the commercially available complex [Co(dmgH)₂(py)Cl] and demonstrate that these double and single complex salts are potent catalysts for the light‐driven HER. We also show that scanning electrochemical cell microscopy can be used to deposit arrays of catalysts [Co(dmgH)₂(py)₂]⁺[Co(dmgBPh₂)₂Cl₂]⁻, TBA+[Co(dmgBPh2)2Cl2]- and [Co(dmgH)₂(py)Cl] on supported and free‐standing amino‐terminated ∼1‐nm‐thick carbon nanomembranes (CNMs). Photocatalytic H₂ evolution at such arrays was quantified with Pd microsensors by scanning electrochemical microscopy, thus providing a new approach for catalytic evaluation and opening up novel routes for the creation and analysis of “designer catalyst arrays”, nanoprinted in a desired pattern on a solid support.

Fundamental Characterization, Photophysics and Photocatalysis of a Base Metal Iron(II)-Cobalt(III) Dyad

A new base metal iron-cobalt dyad has been obtained by connection between a heteroleptic tetra-NHC iron(II) photosensitizer combining a 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine with 2,6-bis(3-methyl-imidazol-2-ylidene)-4,4'-bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)-cobalt(III) assembly has been extensively characterized by ground- and excited-state methods like X-ray crystallography, X-ray absorption spectroscopy, (spectro-)electrochemistry, and steady-state and time-resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited-state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability. Transient absorption spectroscopy after excitation into the metal-to-ligand charge transfer absorption band suggests a relaxation cascade originating from hot singlet and triplet MLCT states, leading to the population of the 3 MLCT state that exhibits the longest lifetime. Finally, decay into the ground state involves a 3 MC state. Attachment of cobaloxime to the iron photosensitizer increases the 3 MLCT lifetime at the iron centre. Together with the directing effect of the linker, this potentially makes the dyad more active in photocatalytic proton reduction experiments than the analogous two-component system, consisting of the iron photosensitizer and Co(dmgH)2 (py)Cl. This work thus sheds new light on the functionality of base metal dyads, which are important for more efficient and sustainable future proton reduction systems.

Triplet Excited States Modulated by Push-Pull Substituents in Monocyclometalated Iridium(III) Photosensitizers

A series of novel monocyclometalated [Ir(tpy)(btp)Cl]⁺ complexes (Ir2-Ir5) were synthesized using 2,2':6',2″-terpyridine (tpy) and 2-(2-pyridyl)benzo[b]thiophene (btp) ligands, as well as their derivatives bearing electron-donating tert-butyl (t-Bu) and electron-withdrawing trifluoromethyl (CF₃) groups. Ir2-Ir5 exhibited visible-light absorption stronger than that of the known complex [Ir(tpy)(ppy)Cl]⁺ (Ir1; ppy = 2-phenylpyridine). Spectroscopic and computational studies revealed that two triplet states were involved in the excited-state dynamics. One is a weakly emissive and short-lived ligand to ligand charge-transfer (LLCT) state originating from the charge transfer from the btp to the tpy ligand. The other is a highly emissive and long-lived ligand-centered (LC) state localized on the btp ligand. Interestingly, the excited state dominant with ³LLCT was completely changed to the ³LC state upon the introduction of substituents on both the tpy and btp ligands. For instance, the excited state of the parent complex Ir2 was weakly emissive (Φ = 2%) and short-lived (τ = 110 ns) in CH₂Cl₂; conversely, Ir5, fully furnished with t-Bu and CF₃ groups, displayed intense phosphorescence with a prolonged lifetime (τ = 14 μs). This difference became increasingly prominent when the solvent was changed to aqueous CH₃CN, most probably due to the ³LLCT stabilization. The predominant excited-state nature was switchable between the ³LLCT and ³LC states depending on the substituents employed; this was demonstrated through investigations of Ir3 and Ir4, bearing either the t-Bu or the CF₃ group, where the complexes exhibited properties intermediate between those of Ir2 and Ir5. All of the Ir(III) complexes were tested as photosensitizers in photocatalytic H₂ evolution over a Co molecular catalyst, and Ir5 outperformed the others, including Ir1, due to improvement in the following key properties: visible-light-absorption ability, excited-state lifetime, and reductive power of the one-electron-reduced species against the catalyst.

Substituted 2,4-Di(pyridin-2-yl)pyrimidine-Based Ruthenium Photosensitizers for Hydrogen Photoevolution under Red Light

The photocatalytic reduction of water to form hydrogen gas (H₂) is a promising approach to collect, convert, and store solar energy. Typically, ruthenium tris(bipyridine) and its many derivatives are used as photosensitizers (PSs) in a variety of photocatalytic conditions. The bis(terpyridine) analogues, however, have only recently gained attention for this application because of their poor photophysical properties. Yet, by the introduction of electron-donating or -withdrawing groups on the terpyridine ligands, the photophysical and electrochemical properties can be considerably improved. In this study, we report a series of nonsymmetric 2,6-di(pyridin-2-yl)pyrimidine ligands with peripheral pyridine substituents in different positions and their corresponding ruthenium(II) complexes. The presence of the pyrimidine ring stabilizes the lowest unoccupied molecular orbital, leading to a red-shifted emission and prolonged excited-state lifetimes as well as higher luminescence quantum yields compared to analogous terpyridine complexes. Furthermore, all complexes are easier to reduce than the previously reported bis(terpyridine) complexes used as PSs. Interestingly, the pyridine substituent in the 4-pyrimidine position has a greater impact on both the photophysical and electrochemical properties. This correlation between the substitution pattern and properties of the complexes is further investigated by using time-dependent density functional theory. In hydrogen evolution experiments under blue- and red-light irradiation, all investigated complexes exhibit much higher activity compared to the previously reported ruthenium(II) bis(terpyridine) complexes, but none of the complexes are as stable as the literature compounds, presumably because of an additional decomposition pathway of the reduced PS competing with electron transfer from the reduced PS to the catalyst.

Merging Two Functions in a Single Rh Catalyst System: Bimodular Conjugate for Light-Induced Oxidative Coupling

A single molecular rhodium catalyst system (PC2-Cp^#Rh^III) bearing two functional domains for both photosensitization and C-H carbometalation was designed to enable an intramolecular redox process. The hypothesized charge-transfer species (PC2^•--Cp^#Rh^IV) was characterized by spectroscopic and electrochemical analyses. This photoinduced internal oxidation allows a facile access to the triplet state of the key post-transmetalation intermediate that readily undergoes C-C bond-forming reductive elimination with a lower activation barrier than in its singlet state, thus enabling catalytic C-H arylation and methylation processes.

The odyssey of cobaloximes for catalytic H2 production and their recent revival with enzyme-inspired design

Cobaloxime complexes gained attention for their intrinsic ability of catalytic H₂ production despite their initial emergence as a vitamin B12 model. The simple, robust, and synthetically manoeuvrable cobaloxime core represents a model catalyst molecule for the investigation of optimal conditions for both photo- and electrocatalytic H₂ production catalytic assemblies. Cobaloxime is one of the rare catalysts that finds equal applications in the analysis of homogeneous and heterogeneous catalytic conditions. However, the poor aqueous solubility and long-term instability of cobaloximes have severely impeded their growth. Lately, interest in the cobaloxime-based catalysts has been resuscitated with the rational use of extended enzymatic features. This unique enzyme-inspired catalyst design strategy has instigated the formation of a new genre of cobaloxime molecules that exhibit enhanced photo- and electrocatalytic H₂ evolution with improved aqueous and air stability.

Conjugated nanoporous polycarbazole bearing a cobalt complex for efficient visible-light driven hydrogen evolution

A conjugated nanoporous polycarbazole (CNP) cross-linked by pyridine and coordinated to Co(iii) displays high catalytic performance for visible light-driven H₂ generation.

Computational Investigation into the Ni(SeNHC2(CN)2)2 and Ni(SNHC2(CN)2)2 Complexes as Potential Catalysts for Hydrogen Production

To reduce our carbon footprint, we must look at alternative non-carbon-containing fuels to prevent continued global climate change. One environmentally friendly alternative fuel is molecular hydrogen. Herein the Ni(SeNHC₂(CN)₂)₂ complex was studied using DFT to determine the thermodynamics associated with the electrocatalytic formation of H₂(g). From the calculated thermodynamics, it appears that the Ni(SeNHC₂(CN)₂)₂ complex is predicted to catalyze the production of H₂ gas under mildly reducing conditions relative to the SHE. Notably, the thermodynamics are better than the values calculated for the analogous Ni(SNHC₂(CN)₂)₂ complex which has been shown experimentally to catalyze the formation of H₂ gas in aqueous solution. Regarding possible kinetic reactivity, the HOMO-LUMO gap energies were calculated. From the gap energies, it is expected that the Se-containing compounds would be more reactive to electron transfer in the third reduction step, meaning therefore that a smaller overpotential would be needed to drive the reduction of Red2-H₂ relative to ^SRed2-H₂ in agreement with past experimental work. Thus, the use of Se in such compounds may offer a means to improve the catalysts for H₂ production.

Targeting G-Rich DNA Structures with Photoreactive Bis-Cyclometallated Iridium(III) Complexes

The synthesis and characterisation of three novel iridium(III) bis-cyclometallated complexes is reported. Their photophysics have been fully characterised by classical methods and revealed charge-transfer (CT) and ligand-centred (LC) transitions. Their ability to selectively interact with G-quadruplex telomeric DNA over duplex DNA has been studied by circular dichroism (CD), bio-layer interferometry (BLI) and surface plasmon resonance (SPR) analyses. Interestingly, one of the complexes was able to promote photoinduced electron transfer (PET) with the guanine DNA base, which in turn led to oxidative damage (such as the formation of 8-oxoguanine) to the telomeric sequence. To the best of our knowledge, this is the first study of highly photo-oxidising bis-cyclometallated iridium(III) complexes with G-quadruplex telomeric DNA.

Photocatalytic Hydrogen Evolution Driven by a Heteroleptic Ruthenium(II) Bis(terpyridine) Complex

Since the initial report by Lehn et al. in 1979, ruthenium tris(bipyridine) ([Ru(bpy)₃]²⁺) and its numerous derivatives were applied as photosensitizers (PSs) in a large panel of photocatalytic conditions while the bis(terpyridine) analogues were disregarded because of their low quantum yields and short excited-state lifetimes. In this study, we prepared a new terpyridine ligand, 4'-(4-bromophenyl)-4,4‴:4″,4‴'-dipyridinyl- 2,2':6',2″-terpyridine (Bipytpy) and used it to prepare the heteroleptic complex [Ru(Tolyltpy)(Bipytpy)](PF₆)₂ (1; Tolyltpy = 4'-tolyl-2,2':6',2'-terpyridine). Complex 1 exhibits enhanced photophysical properties with a higher quantum yield (7.4 × 10^-4) and a longer excited-state lifetime (3.8 ns) compared to those of [Ru(Tolyltpy)₂](PF₆)₂ (3 × 10^-5 and 0.74 ns, respectively). These enhanced photophysical characteristics and the potential for PS-catalyst interaction through the peripheral pyridines led us to apply the complex for visible-light-driven hydrogen evolution. The photocatalytic system based on 1 as the PS, triethanolamine as a sacrificial donor, and cobaloxime as a catalyst exhibits sustained activity over more than 10 days under blue-light irradiation (light-emitting diode centered at 450 nm). A maximum turnover number of 764 was obtained after 12 days.

Ruthenium(iii)-bis(phenolato)bipyridine/TiO2 hybrids: unprecedented photocatalytic hydrogen evolution

In this work, two new bis-(hydroxyphenyl)bipyridine based ruthenium complexes with 4-picoline (coded as MCS-B4M) and isonicotinic acid (coded as MCS-B5M), which act as ancillary ligands, have been synthesized and employed for the first time as photosensitizers in photocatalytic hydrogen evolution studies. The photocatalyst MCS-B5M/TiO₂-Pt showed an impressive hydrogen generation rate of up to 4.2 mmol h^-1 and turnover number (TON) of 84 959 after 5 h. The better performance of B5TP over B4TP was due to the higher excited state lifetime of MCS-B5M (∼2.6 ns) than that of MCS-B4M (∼1.4 ns). This leads to a higher probability of electron transfer to the TiO₂/Pt composite in the case of the former and a stronger coupling of MCS-B5M excited states with the conduction band of the TiO₂/Pt composite by the -COOH linkers of the isonicotinic acid moiety, resulting in better photosensitization as observed in the UV-Vis (DRS mode) absorbance study. The comparative study of the two dyes clearly shows the manifestations of their respective ancillary ligands having contrasting electronic properties. This work gives a new class of ruthenium photosensitizers as efficient light harvesting photocatalysts.

Design and photophysical studies of iridium(iii)–cobalt(iii) dyads and their application for dihydrogen photo-evolution

We report several new dyads constituted of cationic iridium(iii) photosensitizers and cobalt(iii) catalyst connected via free pendant pyridine on the photosensitizers.

Heteroleptic ruthenium bis-terpyridine complexes bearing a 4-(dimethylamino)phenyl donor and free coordination sites for hydrogen photo-evolution

Three new ruthenium bis-terpyridine complexes bearing both an internal electron donor and peripheral coordination site(s) are used as photosensitisers in H₂ photo-evolution under blue and green light with sustained activity for at least two days.

Photofunctions of iridium(iii) complexes in vesicles: long-lived excited states and visible-light sensitization for hydrogen evolution in aqueous solution

Utilization of DPPC vesicles allows water-insoluble photoactive Ir(iii) complexes to be dispersed in bulk aqueous solution.

Mini-review on an engineering approach towards the selection of transition metal complex-based catalysts for photocatalytic H2 production

Advances in transition-metal (Ru, Co, Cu, and Fe) complex-based catalysts since 2000 are briefly summarized in terms of catalyst selection and application for photocatalytic H₂ evolution.

Mimicking 2,2′:6′,2′′:6′′,2′′′-quaterpyridine complexes for the light-driven hydrogen evolution reaction: synthesis, structural, thermal and physicochemical characterizations

The synthetic difficulties associated with quaterpyridine (qtpy) complexes have limited their use in the formation of various metallosupramolecular architectures in spite of their diverse structural and physicochemical properties. Providing a new facile synthetic route to the synthesis of functionalised qtpy mimics, we herein report the synthesis of three novel –NH₂ functionalized qtpy-like complexes 12–14 with the general formula M(C₁₆H₁₄N₁₂)(NO₃)₂ (M = Co(ii), Ni(ii) and Cu(ii)) in high yield and purity. Characterization of these complexes has been done by single crystal X-ray diffraction (SCXRD), thermogravimetric analysis, UV-Vis, infrared, mass spectrometry and cyclic voltammetry. As indicated by SCXRD, in all the synthesized complexes, the metal ions show a strongly distorted octahedral coordination geometry and typical hydrogen bonding networks involving DAT groups. In addition, complexes 12–14 have been analyzed as potential photocatalysts for hydrogen evolution reaction (HER) displaying good turnover numbers (TONs). Hydrogen produced from these photocatalysts can serve as the possible alternative for fossil fuels. To the best of our knowledge, this is the only study showcasing –NH₂ functionalized qtpy-like complexes of Co(ii), Ni(ii) and Cu(ii) and employing them as photocatalysts for HER. Thus, a single proposed strategy solves two purposes-one related to synthesis while second is related to our environment.

Facile synthesis of three novel –NH₂ functionalized qtpy-like complexes, their characterizations and study of their photocatalytic properties for hydrogen evolution reaction.

A supramolecular assembly bearing an organic TADF chromophore: synthesis, characterization and light-driven cooperative acceptorless dehydrogenation of secondary amines

A noble-metal-free chromophore–catalyst supramolecular assembly, which contains an organic thermally activated delayed fluorescence (TADF) chromophore and cobaloximes, has been designed and synthesized for efficient light-driven acceptorless dehydrogenation of secondary amines.

Trifluoromethyl-Substituted Iridium(III) Complexes: From Photophysics to Photooxidation of a Biological Target

Photodynamic therapeutic agents are of key interest in developing new strategies to develop more specific and efficient anticancer treatments. In comparison to classical chemotherapeutic agents, the activity of photodynamic therapeutic compounds can be finely controlled thanks to the light triggering of their photoreactivity. The development of type I photosensitizing agents, which do not rely on the production of ROS, is highly desirable. In this context, we developed new iridium(III) complexes which are able to photoreact with biomolecules; namely, our Ir(III) complexes can oxidize guanine residues under visible light irradiation. We report the synthesis and extensive photophysical characterization of four new Ir(III) complexes, [Ir(ppyCF₃)₂(N^N)]⁺ [ppyCF₃ = 2-(3,5-bis(trifluoromethyl)phenyl)pyridine) and N^N = 2,2'-dipyridyl (bpy); 2-(pyridin-2-yl)pyrazine (pzpy); 2,2'-bipyrazine (bpz); 1,4,5,8-tetraazaphenanthrene (TAP)]. In addition to an extensive experimental and theoretical study of the photophysics of these complexes, we characterize their photoreactivity toward model redox-active targets and the relevant biological target, the guanine base. We demonstrate that photoinduced electron transfer takes place between the excited Ir(III) complex and guanine which leads to the formation of stable photoproducts, indicating that the targeted guanine is irreversibly damaged. These results pave the way to the elaboration of new type I photosensitizers for targeting cancerous cells.

Photocatalytic H2production by dirhodium(ii,ii) photosensitizers with red light

Photocatalytic H₂evolution uponλ_irr= 655 nm with dirhodium(ii,ii) photosensitizers demonstrates tunable oxidative and reductive quenching mechanisms.

An anionic iridium(iii) complex as a visible-light absorbing photosensitizer

A new anionic Ir(iii) photosensitizer bearing coumarin dyes has been developed and applied to the visible-light-driven hydrogen generation.

Ultrafast charge transfer excited state dynamics in trifluoromethyl-substituted iridium(iii) complexes

Ultrafast spectroscopic studies on the excited state interplay in trifluoromethyl-substituted iridium(iii) complexes.

A Bisamide Ruthenium Polypyridyl Complex as a Robust and Efficient Photosensitizer for Hydrogen Production

A photosensitizer based on a ruthenium complex of a bisamide-polypyridyl ligand gives rise to a large improvement in photocatalytic stability, rate of activity, and efficiency in photocatalytic H₂ production compared to [Ru(bpy)₃ ]²⁺ (bpy=2,2'-bpyridine). The bisamide ruthenium polypyridyl complex combined with a cobaltoxime-based photocatalyst was found to be highly efficient under blue-light (turnover number (TON)=7800) and green-light irradiation (TON=7200) whereas [Ru(bpy)₃ ]²⁺ was significantly less effective with a TON of 2600 and 1100, respectively. The greatest improvement was under red-light-emitting diodes, with bisamide ruthenium polypyridyl complex and cobaltoxime exhibiting a TON of 4200 compared to [Ru(bpy)₃ ]²⁺ and cobaltoxime at a TON of only 71.

Facile One-Pot Synthesis of Ruthenium(II) Quaterpyridine-Based Photosensitizers for Photocatalyzed Hydrogen Production

We present here the efficient microwave-assisted synthesis and photophysical study of a family of ruthenium(II) complexes of the general formula [Ru(bpy)_x(qpy)_3-x]²⁺ (where bpy = 2,2'-bipyridine, qpy = 4,4':2',2″:4″,4‴-quaterpyridine, and x = 0, 1, 2 giving compounds 1 = [Ru(bpy)₂(qpy)₁]²⁺, 2 = [Ru(bpy)₁(qpy)₂]²⁺, and 3 = [Ru(qpy)₃]²⁺). Compared to the standard reference, [Ru(bpy)₃]²⁺ (τ = 870 ns, Φ = 9.5%), the complexes display longer-lived excited state lifetimes at room temperature (τ: 1 = 1440 ns, 2 = 1640 ns, 3 = 1780 ns) and improved quantum yields (Φ: 1 = 14%, 2 = 19%, 3 = 23%). Theoretical calculations were performed to support the interpretation of these photophysical properties. These complexes are excellent photosensitizers as they absorb light throughout the visible spectrum, have excellent excited state lifetimes at room temperature, and have high quantum yields. In combination with a cobalt dimethylglyoxime catalyst, they exhibit remarkable hydrogen evolution with blue light, and they are far more efficient than the reference in the field, [Ru(bpy)₃]²⁺.