Efficient Photogeneration of Hydrogen Boosted by Long-Lived Dye-Modified Ir(III) Photosensitizers and Polyoxometalate Catalyst
Developing efficient catalysts and photosensitizers is crucial for the construction
of effective photocatalytic H2-evolving systems. Here, we report the facile preparation of Coumarin-modified Ir(III)
complexes (
Introduction
Since the Industrial Revolution in the 19th century, the continuous depletion of traditional fossil fuels has caused serious energy shortages and environmental challenges. To solve these problems, great efforts have been devoted to developing cost-effective, clean, and sustainable energy alternatives. As one of the widely studied renewable energy exploration strategies, solar-driven water splitting into H2 and O2 is a promising pathway to convert and store solar energy into renewable chemical bonds.1–4 In the past few decades, considerable attention has been paid to establishing highly efficient photocatalytic water splitting systems.1,3–8 For the catalytic hydrogen evolution half-reaction, the most widely adopted system consists of three components containing photosensitizer, a catalyst, and a sacrificial reagent.4,9–11 Notwithstanding, key issues have been identified regarding the exploration of viable, efficient, and inexpensive water reduction catalysts (WRCs), as well as the design of tunable, stable, and strong visible-light-responsive photosensitizers.12–16
As an emerging type of multielectron-transfer WRCs, transition-metal-substituted polyoxometalates (TMSPOMs) with tunable structural compositions, physicochemical, and photochemical properties, could combine the advantages of both heterogeneous metal oxide catalysts (e.g., stability) and homogeneous molecular catalysts (e.g., high activity, selectivity, and tunability).2,17–21 After years of numerous efforts, a series of Mn, Ni, Co, and Cu-substituted POMs have been synthesized and studied for catalytic H2 evolution when coupled with visible-light-absorbing photosensitizers and sacrificial reagents.19,21–25 Although TMSPOMs have shown great potential applications in various H2-evolving systems, the challenges facing these systems remain substantial. To date, the most widely used photosensitizers in POM-catalyzed H2-evolving systems are limited to noble metal-based organometallic complexes such as [Ru(bpy)3]2+, [Ir(ppy)2(dtbbpy)]+ and their derivatives,21–24,26–29 as well as pure organic chromophores, including eosin Y, fluorescein, rhodamine, and others.30–32 Such noble metal-based organometallic complexes usually exhibit a long-lived triplet state (3MLCT) to promote photocatalytic hydrogen evolution.4,12,33–38 However, they often suffer from low molar absorption coefficients and narrow visible-light-absorbing range.4,12,39 Meanwhile, pure organic chromophores generally show very high molar absorption coefficients. Nonetheless, the short-lived excited states and poor photostability hinder their practical application in photocatalysis considerably. To improve the solar-to-energy conversion efficiency, some pioneering research studies have reported the construction of strong visible-light-absorbing chromophores via covalently decorating organometallic photosensitizers with organic dyes.38,40–47 For example, sensitization of colloidal Pt-TiO2 with Bodipy or Rhodamine-modified platinum diimine dithiolate (PtN2S2) charge-transfer chromophore could enhance the photocatalytic hydrogen evolution efficiency remarkably with substantial longevity and high turnover numbers (TONs).44,46 Also, the modification of [Ir(ppy)2(bpy)]+ with two different organic dyes greatly increased the visible-light-absorbing ability and hydrogen evolution activity in the presence of [CoIII(dmgH)2(py)Cl] catalyst.47 Although many of these works reported extremely high TONs with respect to the photosensitizers, the TONs versus H2-evolving catalysts are usually unsatisfactory. Moreover, among various dye-modified chromophores, none was applied as light-absorbers to drive catalytic reactions in POM-catalyzed H2-evolving systems. We considered that employing the strong visible-light-absorbing ability of Coumarin 6 chromophore (ε < 105 M−1 cm−1) and the good coordinating ability as the C^N ligand to iridium metal center would be a promising strategy to enhance the photocatalytic performance of POM-catalyzed H2-evolving system, as this approach would combine the advantages of high visible-light-absorbing ability of Coumarin 6 and long-lasting triplet states of potential Ir(III) complexes.
Herein, in this context, we prepared different Coumarin-modified Ir(III) complexes
(denoted as
Experimental Methods
Materials
2-Phenylpyridine, 4,4′-di-tert-butyl-2,2′-bipyridine, 4,4′-dibromo-2,2′-bipyridine, 3-(2-benzothiazolyl)-7-(diethylamino)coumarin
(Coumarin 6), 2-tributylstannylthiophene ligands, and Iridium(III) chloride trihydrate
were used as received without further purification. Catalyst K6Na[Ni3(H2O)3PW10O39H2O]•12H2O (K6Na-
Synthesis of 4,4′-di(thien-2-yl)-2,2′-bipyridine (spy)
4,4′-Dibromo-2,2′-bipyridine (0.5 g, 1.6 mmol, 1.0 equiv), 2-tributylstannylthiophene (1.5 g, 4.0 mmol, 2.5 equiv), [Pd (PPh)3Cl2] (67 mg, 95.5 μmol, 0.06 equiv), and CsF (1.0 g, 6.4 μmol, 4.0 equiv) were suspended in a 12 mL degassed solution mixture of toluene/tetrahydrofuran (THF) (2/1). After several degassing and argon bubbling times, the mixture was stirred and heated at 110 °C for 6 h. The resulting mixture was poured into MeOH that afforded a dark grey precipitate, which was filtered off, washed with MeOH, a small quantity of dichloromethane (DCM), and diethyl ether to produce a pure light grey solid product. Yield: 90%; proton nuclear magnetic resonance (1H NMR; 400 MHz, CDCl3, 298 K, δ): 8.70–8.67 (m, 2H), 7.67 (dd, 1H, J = 3.64, 0.84 Hz), 7.53 (dd, 1H, J = 5.04, 1.96 Hz), 7.44 (dd, 1H, J = 5.04, 0.88 Hz), 7.16 (dd, 1H, J = 5.00, 3.72 Hz). High-resolution mass spectrometry (HRMS) (electrospray ionization mass spectrometry [ESI-MS]) (m/z): [M]+ calcd for [C18H13N2S2], 321.0520; found, 321.0500.
Synthetic procedure for iridium complexes
Synthesis of PS-1
Iridium(III) chloride (450 mg, 1.28 mmol, 1.0 equiv) and 2-phenylpyridine (440 mg,
2.82 mmol, 2.2 equiv) were suspended in 30 mL 2-methoxyethanol/water (3:1 v/v) solution,
and the mixture was heated at 110 °C for 48 h under argon conditions. After completion,
the solution was cooled to room temperature, then the precipitate was filtered off,
washed with water and EtOH to afford a solid orange Ir(III) μ-chloro-bridged dimer
product. The resulting Ir(III) μ-chloro-bridged dimer complex (200 mg, 0.19 mmol,
1.0 equiv) and 4,4′-di-tert-butyl-2,2′-bipyridine (110 mg, 0.41 mmol, 2.2 equiv) were suspended in 10 mL of 2-methoxyethanol
solution, and the mixture was heated at 110 °C for 12 h under argon conditions. After
cooling to room temperature, an excess NH4PF6 aqueous solution was added to the above solution and stirred for 4 h at room temperature.
The resulting precipitate was filtered off, washed with water and EtOH, and the crude
product was purified by silica gel column chromatography using dichloromethane/MeOH
(v/v = 1/0 to 200/1) as the eluent, affording the pure product
Synthesis of PS-2
Iridium(III) chloride (450 mg, 1.28 mmol, 1.0 equiv) and Coumarin 6 (990 mg, 2.82 mmol,
2.2 equiv) were suspended in 30 mL 2-methoxyethanol/water (3:1 v/v) solution; the
mixture was heated at 110 °C for 48 h under argon conditions. After completion, the
solution was cooled to room temperature, then the precipitate was filtered off, washed
with water and EtOH, affording Ir(III) μ-chloro-bridged dimer product as orange solid.
Subsequently, the resulting Ir(III) μ-chloro-bridged dimer complex (200 mg, 0.11 mmol,
1.0 equiv) and 4,4′-di-tert-butyl-2,2′-bipyridine (65 mg, 0.24 mmol, 2.2 equiv) were suspended in 10 mL of 2-methoxyethanol
solution, and the mixture was heated at 110 °C for 12 h under argon conditions. After
cooling to room temperature, an excess NH4PF6 aqueous solution was added to the above solution and stirred for 4 h at room temperature.
The resulting precipitate was filtered off, washed with water and EtOH, the crude
product was purified by silica gel column chromatography using dichloromethane/MeOH
(v/v = 1/0 to 200/1) as the eluent, affording the pure product
Synthesis of PS-3
To synthesize
Instrumentation
1H NMR spectra were recorded on a Bruker Ascend 400M (Avance IIIHD 400 MHz) Fourier transform NMR spectrometer (Bruker, Germany) with chemical shifts (δ, ppm) relative to tetramethylsilane (Me4Si). High-resolution ESI-MS was performed using AGILENT Q-TOF 6520 mass spectrometer (Agilent, United States). Infrared spectra were acquired on a Bruker TENSOR II FT-IR spectrometer by preparing dry solid samples mixed with KBr pellets. The X-ray diffraction data were obtained using a Bruker APEXII DUO CMOS detector with monochromated Mo-Kα radiation. Cell refinement and data reduction were processed with the Protenum2 program package.51 Using olex2, the molecular structure was solved with the ShelXS structure solution program using direct methods and refined using the XL refinement package with least-squares minimization.52 Then all non-H atoms of the complexes were refined with anisotropic thermal parameters. Subsequently, the hydrogen atoms were included in idealized positions and refined using fixed geometry relative to their carrier atoms. Crystal structure graphics and their corresponding packing diagrams were acquired using software Mercury 2.4.5 (Cambridge Crystallographic Data Centre, Cambridge). UV–vis absorption spectra following recording on a UV 2600 UV–vis spectrophotometer and all emission spectra were performed on spectrofluorometer FS5 (Edinburgh Instruments Ltd., Edinburgh); errors for λ values (±1 nm) were estimated. The emission lifetime was measured using an EPL-450 picosecond pulsed diode (Edinburgh Instruments Ltd.) laser system (pulse output 450 nm). These long-lived triplet decay kinetic curves were fitted by a single-exponential decay function. Cyclic voltammetry was recorded on a CHI660E Electrochemical Workstation (Shanghai Chenhua Company, Shanghai, China). The experimental data were collected at a scan rate of 100 mV s−1. The working electrode was polished with 0.05 μm alumina, sonicated with deionized water, rinsed with EtOH, and then with deionized water before use. The reference and the counter electrodes were Ag/Ag+ (0.1 M TBAPF6 and 0.01M AgNO3 in acetonitrile) and a platinum wire, respectively. Solutions were degassed for 10 min by N2 before experiments. The E1/2 of the ferrocenium/ferrocene couple (Fc+/Fc) was measured in the same solution as samples and was used as an internal reference.
Photocatalytic hydrogen production experiments
The photocatalytic hydrogen production was performed in deaerated CH3CN-DMF (v/v = 3/2) solution with TEOA (0.25 M) as a sacrificial electron donor, H2O (2 M) as a proton source, iridium complexes (200 μM) as photosensitizers, and Ni-substituted
polyoxometalate (
Density functional theory calculations
Density functional theory (DFT) calculations were performed using B3LYP functional with Grimme’s D3 dispersion correction. The 6-31G(d) basis set was applied on nonmetal atoms, and the Lanl2DZ basis set was used on the Ir atom. The continuum solvation model based on density (SMD) with solvent CH3CN was used to address the solvent effect. The calculations were carried out using the Gaussian09 program (refer to the Supporting Information for details).
Results and Discussion
Syntheses and characterization
The structures of bis-cyclometalated Ir(III) complexes (denoted as
Figure 1 | Structures of (a) photosensitizers PS-1, PS-2, and PS-3, and (b) Ni3PW10. (c) Top and (d) side views of single-crystal structures of Ir(III) complexed PS-2.
Needle-shaped single crystals of
Scheme 1 | Synthetic route for Coumarin-modified photosensitizers PS-2 and PS-3.
Photophysical properties
The photophysical properties of the
Figure 2 | (a) UV–vis absorption, (b) emission spectra of PS-1 (λex = 400 nm), PS-2 (λex = 440 nm), and PS-3 (λex = 440 nm) in CH3CN (C = 10 μM) under air. (c) Comparison of PS-2 emission under N2 and air conditions. The decay of (d) PS-1 (λem = 570 nm), (e) PS-2 (λem = 587 nm), and (f) PS-3 (λem = 575 nm) in CH3CN (C = 10 μM) excited at 450 nm under N2.
The emission spectra of
Visible-light-driven hydrogen evolution
The photocatalytic hydrogen production was conducted in deaerated CH3CN-DMF (v/v = 3/2) solution with TEOA as sacrificial electron donor, H2O as proton source, Ir(III) complexes as photosensitizers, and
Figure 3 | Photocatalytic H2 generation of PS-2 and PS-3 in (a) 6 h and (b) 120 h under the condition of catalyst Ni3PW10 (20 μM), PS (0.2 mM), TEOA (0.25 M), H2O (2 M), 6 mL CH3CN-DMF (v/v = 3/2); Control experiments (c) based on different components (catalyst
Ni3PW10 20 μM, PS-2 0.2 mM, TEOA 0.25 M) as well as by varying the concentration of (d) Ni3PW10 (0–40 μM), (e) PS-2 (0–0.3 mM), and (f) TEOA (0–0.25 M). Conditions: Xe lamp (λ < 400 nm, 300 W, 20 °C),
H2O (2 M), 6 mL CH3CN-DMF (v/v = 3/2), 6 h.
Various control experiments have been performed to study the effect of each component
in the
To better understand the excited-state characteristics of different complexes and
the origin of the high performance of
To uncover the intramolecular energy transfer process, the fs-TA measurements of Coumarin
6 ligand and
Luminescence quenching studies
Next, we unveiled the photocatalytic mechanism and electron-transfer dynamics by employing
both steady-state and time-resolved fluorescence spectroscopy to investigate the luminescence
quenching of
Figure 4 | (a) Emission quenching and (b) decay kinetics of PS-2 (0.2 mM) by Ni3PW10 (20 μM) and TEOA (0.25 M) in CH3CN-DMF (v/v = 3/2) solution under N2 condition (λex = 400 nm for emission, λem = 585 nm for decay); Phosphorescence quenching of PS-2 (0.2 mM) by changing the concentration of (c) Ni3PW10 (0–50 μM) and (d) TEOA (0–0.25 M).
Condition | Sample | Ksv (M−1)a | Ksv (M−1)b | koq (M−1s−1)c | krq (M−1 s−1)d |
---|---|---|---|---|---|
|
|
10,169.49 | 13.31 | 3.6 × 1010 | 4.7 × 107 |
|
|
2924.27 | 1.22 | 2.8 × 109 | 1.1 × 106 |
|
|
2303.40 | 1.60 | 2.0 × 109 | 1.4 × 106 |
|
|
626.54 | 3.01 | 7.6 × 109 | 3.6 × 107 |
|
|
1613.75 | 0.34 | 5.9 × 109 | 1.2 × 106 |
|
|
2088.00 | 1.76 | 4.5 × 109 | 3.8 × 106 |
Electrochemical studies
Further, we employed electrochemical studies to investigate the electron-transfer
thermodynamics and elucidate the distinguished activities of different photosensitizers
for catalytic hydrogen production. Cyclic voltammograms (CVs) of components
Eox | Ered | E0,0 | ΔGCSa | ΔGCSb | ΔGCSc | |
---|---|---|---|---|---|---|
|
1.42 | −1.64 | 2.51 | −0.14 | −0.96 | −1.51 |
|
1.08 | −1.26, −1.53, −1.80 | 2.41 | −0.42 | −1.20 | −1.39 |
|
1.01 | −1.20, −1.44 | 2.45 | −0.52 | −1.31 | −1.07 |
|
−0.13 | |||||
|
0.73 |
Computational study
To uncover the nature of the frontier molecular orbitals and the difference in the
HOMO–LUMO gap between
Figure 5 | (a) The frontier molecular orbitals and HOMO–LUMO gap of PS-2 and PS-3 at ground state as calculated by B3LYP method. (b) Proposed mechanism for the photocatalytic
process of Coumarin-modified PS.
Proposed photocatalytic mechanism
Based on the above studies, a mechanism for the photocatalytic H2 generation using Coumarin-modified PS was proposed (Figure 5b), as follows: Upon illumination by strong visible light, the photosensitizer is excited
from the singlet ground state to singlet excited state, which can further transfer
to triplet excited state through efficient ISC. The resulting triplet 3[Coumarin-Ir]+* could be either reductively quenched by TEOA or oxidatively quenched by
Conclusion
Coumarin 6 dye was incorporated into bis-cyclometalated Ir(III) complexes to enhance
their photosensitivity to visible light. The obtained Coumarin-modified Ir(III) chromophores
(
Supporting Information
Supporting Information is available and includes other detailed experimental procedures, data, X-ray crystallographic
data for
Conflict of Interest
There is no conflict of interest to report.
Funding Information
The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (nos. 21871025 and 21831001), the Recruitment Program of Global Experts (Young Talents), and the BIT Teli Young Fellow Program.
Acknowledgments
The authors sincerely acknowledge Prof. Meng Zhou (University of Science and Technology of China) and Assist. Prof. Kai Li (Shenzhen University) for their helpful discussion on transient absorption spectra and photophysical data analyses, respectively.
References
- 1. Esswein A. J.; Nocera D. G.Hydrogen Production by Molecular Photocatalysis.Chem. Rev.2007, 107, 4022–4047. Google Scholar
- 2. Lv H.; Geletii Y. V.; Zhao C. C.; Vickers J. W.; Zhu G. B.; Luo Z.; Song J.; Lian T. Q.; Musaev D. G.; Hill C. L.Polyoxometalate Water Oxidation Catalysts and the Production of Green Fuel.Chem. Soc. Rev.2012, 41, 7572–7589. Google Scholar
- 3. Han Z. J.; Eisenberg R.Fuel from Water: The Photochemical Generation of Hydrogen from Water.Acc. Chem. Res.2014, 47, 2537–2544. Google Scholar
- 4. Yuan Y. J.; Yu Z. T.; Chen D. Q.; Zou Z. G.Metal-Complex Chromophores for Solar Hydrogen Generation.Chem. Soc. Rev.2017, 46, 603–631. Google Scholar
- 5. Wang M.; Han K.; Zhang S.; Sun L. C.Integration of Organometallic Complexes with Semiconductors and Other Nanomaterials for Photocatalytic H2 Production.Coord. Chem. Rev.2015, 287, 1–14. Google Scholar
- 6. Berardi S.; Drouet S.; Francas L.; Gimbert-Surinach C.; Guttentag M.; Richmond C.; Stoll T.; Llobet A.Molecular Artificial Photosynthesis.Chem. Soc. Rev.2014, 43, 7501–7519. Google Scholar
- 7. Du P. W.; Eisenberg R.Catalysts Made of Earth-Abundant Elements (Co, Ni, Fe) for Water Splitting: Recent Progress and Future Challenges.Energy Environ. Sci.2012, 5, 6012–6021. Google Scholar
- 8. Li X. B.; Tung C. H.; Wu L. Z.Semiconducting Quantum Dots for Artificial Photosynthesis.Nat. Rev. Chem.2018, 2, 160–173. Google Scholar
- 9. Du P. W.; Knowles K.; Eisenberg R.A Homogeneous System for the Photogeneration of Hydrogen from Water Based on a Platinum(II) Terpyridyl Acetylide Chromophore and a Molecular Cobalt Catalyst.J. Am. Chem. Soc.2008, 130, 12576. Google Scholar
- 10. Jian J. X.; Ye C.; Wang X. Z.; Wen M.; Li Z. J.; Li X. B.; Chen B.; Tung C. H.; Wu L. Z.Comparison of H2 Photogeneration by [FeFe]-Hydrogenase Mimics with CdSe QDs and Ru(bpy)3Cl2 in Aqueous Solution.Energy Environ. Sci.2016, 9, 2083–2089. Google Scholar
- 11. Li X. B.; Gao Y. J.; Wang Y.; Zhan F.; Zhang X. Y.; Kong Q. Y.; Zhao N. J.; Guo Q.; Wu H. L.; Li Z. J.; Tao Y.; Zhang J. P.; Chen B.; Tung C. H.; Wu L. Z.Self-Assembled Framework Enhances Electronic Communication of Ultrasmall-Sized Nanoparticles for Exceptional Solar Hydrogen Evolution.J. Am. Chem. Soc.2017, 139, 4789–4796. Google Scholar
- 12. Zhao J. Z.; Wu W. H.; Sun J. F.; Guo S.Triplet Photosensitizers: From Molecular Design to Applications.Chem. Soc. Rev.2013, 42, 5323–5351. Google Scholar
- 13. Manbeck G. F.; Fujita E.; Brewer K. J.Tetra- and Heptametallic Ru(II), Rh(III) Supramolecular Hydrogen Production Photocatalysts.J. Am. Chem. Soc.2017, 139, 7843–7854. Google Scholar
- 14. Kaeffer N.; Chavarot-Kerlidou M.; Artero V.Hydrogen Evolution Catalyzed by Cobalt Diimine Dioxime Complexes.Acc. Chem. Res.2015, 48, 1286–1295. Google Scholar
- 15. Han Z. J.; McNamara W. R.; Eum M. S.; Holland P. L.; Eisenberg R.A Nickel Thiolate Catalyst for the Long-Lived Photocatalytic Production of Hydrogen in a Noble-Metal-Free System.Angew. Chem. Int. Ed.2012, 51, 1667–1670. Google Scholar
- 16. McNamara W. R.; Han Z. J.; Yin C. J.; Brennessel W. W.; Holland P. L.; Eisenberg R.Cobalt-Dithiolene Complexes for the Photocatalytic and Electrocatalytic Reduction of Protons in Aqueous Solutions.Proc. Natl. Acad. Sci. U. S. A.2012, 109, 15594–15599. Google Scholar
- 17. Wang S. S.; Yang G. Y.Recent Advances in Polyoxometalate-Catalyzed Reactions.Chem. Rev.2015, 115, 4893–4962. Google Scholar
- 18. Sumliner J. M.; Lv H.; Fielden J.; Geletii Y. V.; Hill C. L.Polyoxometalate Multi-Electron-Transfer Catalytic Systems for Water Splitting.Eur. J. Inorg. Chem.2014, 2014, 635–644. Google Scholar
- 19. Guo W.; Lv H.; Chen Z. Y.; Sullivan K. P.; Lauinger S. M.; Chi Y. N.; Sumliner J. M.; Lian T. Q.; Hill C. L.Self-Assembly of Polyoxometalates, Pt Nanoparticles and Metal-Organic Frameworks into a Hybrid Material for Synergistic Hydrogen Evolution.J. Mater. Chem. A2016, 4, 5952–5957. Google Scholar
- 20. Cronin L.; Muller A.From Serendipity to Design of Polyoxometalates at the Nanoscale, Aesthetic Beauty and Applications.Chem. Soc. Rev.2012, 41, 7333–7334. Google Scholar
- 21. Lv H.; Guo W.; Wu K. F.; Chen Z. Y.; Bacsa J.; Musaev D. G.; Geletii Y. V.; Lauinger S. M.; Lian T.; Hill C. L.A Noble-Metal-Free, Tetra-Nickel Polyoxotungstate Catalyst for Efficient Photocatalytic Hydrogen Evolution.J. Am. Chem. Soc.2014, 136, 14015–14018. Google Scholar
- 22. Lv H.; Song J.; Zhu H. M.; Geletii Y. V.; Bacsa J.; Zhao C. C.; Lian T. Q.; Musaev D. G.; Hill C. L.Visible-Light-Driven Hydrogen Evolution from Water Using a Noble-Metal-Free Polyoxometalate Catalyst.J. Catal.2013, 307, 48–54. Google Scholar
- 23. Lv H.; Gao Y. Z.; Guo W.; Lauinger S. M.; Chi Y. N.; Bacsa J.; Sullivan K. P.; Wieliczko M.; Musaev D. G.; Hill C. L.Cu-Based Polyoxometalate Catalyst for Efficient Catalytic Hydrogen Evolution.Inorg. Chem.2016, 55, 6750–6758. Google Scholar
- 24. Lv H.; Chi Y. N.; van Leusen J.; Kogerler P.; Chen Z. Y.; Bacsa J.; Geletii Y. V.; Guo W.; Lian T. Q.; Hill C. L.[{Ni4(OH)3AsO4}4(B-α-PW9O34)4]28−: A New Polyoxometalate Structural Family with Catalytic Hydrogen Evolution Activity.Chem. Eur. J.2015, 21, 17363–17370. Google Scholar
- 25. Zhang G. H.; Yang W. B.; Wu W. M.; Wu X. Y.; Zhang L.; Kuang X. F.; Wang S. S.; Lu C. Z.A Sandwich-Type Polyoxometalate for Efficient Noble-Metal-Free Hydrogen Evolution Upon Visible Light Irradiation.J. Catal.2019, 369, 54–59. Google Scholar
- 26. Matt B.; Fize J.; Moussa J.; Amouri H.; Pereira A.; Artero V.; Izzet G.; Proust A.Charge Photo-Accumulation and Photocatalytic Hydrogen Evolution Under Visible Light at an Iridium(III)-Photosensitized Polyoxotungstate.Energy Environ. Sci.2013, 6, 1504–1508. Google Scholar
- 27. Allmen K.; Moré R.; Müller R.; Soriano-López J.; Linden A.; Patzke G. R.Nickel-Containing Keggin-Type Polyoxometalates as Hydrogen Evolution Catalysts: Photochemical Structure–Activity Relationships.ChemPlusChem2015, 80, 1389–1398. Google Scholar
- 28. Han X. B.; Qin C.; Wang X. L.; Tan Y.-Z.; Zhao X.-J.; Wang E.-B.Bio-Inspired Assembly of Cubane-Adjustable Polyoxometalate-Based High-Nuclear Nickel Clusters for Visible Light-Driven Hydrogen Evolution.Appl. Catal. B2017, 211, 349–356. Google Scholar
- 29. Paille G.; Boulmier A.; Bensaid A.; Ha-Thi M. H.; Tran T. T.; Pino T.; Marrot J.; Rivière E.; Hendon C. H.; Oms O.; Gomez-Mingot M.; Fontecave M.; Mellot-Draznieks C.; Dolbecq A.; Mialane P.An Unprecedented {Ni14SiW9} Hybrid Polyoxometalate with High Photocatalytic Hydrogen Evolution Activity.Chem. Commun.2019, 55, 4166–4169. Google Scholar
- 30. Liu X.; Li Y.; Peng S.; Lu G.; Li S.Photocatalytic Hydrogen Evolution Under Visible Light Irradiation by the Polyoxometalate α-[AlSiW11(H2O)O39]5−-Eosin Y System.Int. J. Hydrogen Energy2012, 37, 12150–12157. Google Scholar
- 31. Zhao J.; Ding Y.; Wei J.; Du X.; Yu Y.; Han R.A Molecular Keggin Polyoxometalate Catalyst with High Efficiency for Visible-Light Driven Hydrogen Evolution.Int. J. Hydrogen Energy2014, 39, 18908–18918. Google Scholar
- 32. Ding Y. S.; Wang H. Y.; Ding Y.Visible-Light-Driven Hydrogen Evolution Using a Polyoxometalate-Based Copper Molecular Catalyst.Dalton Trans.2020, 49, 3457–3462. Google Scholar
- 33. Zhao J. Z.; Ji S. M.; Wu W. H.; Wu W. T.; Guo H. M.; Sun J. F.; Sun H. Y.; Liu Y. F.; Li Q. T.; Huang L.Transition Metal Complexes with Strong Absorption of Visible Light and Long-Lived Triplet Excited States: From Molecular Design to Applications.RSC Adv.2012, 2, 1712–1728. Google Scholar
- 34. Cai J. G.; Yu Z. T.; Yuan Y. J.; Li F.; Zou Z. G.Dinuclear Iridium(III) Complexes Containing Bibenzimidazole and Their Application to Water Photoreduction.ACS Catal.2014, 4, 1953–1963. Google Scholar
- 35. Neubauer A.; Grell G.; Friedrich A.; Bokarev S. I.; Schwarzbach P.; Gartner F.; Surkus A. E.; Junge H.; Beller M.; Kuhn O.; Lochbrunner S.Electron- and Energy-Transfer Processes in a Photocatalytic System Based on an Ir(III)-Photosensitizer and an Iron Catalyst.J. Phys. Chem. Lett.2014, 5, 1355–1360. Google Scholar
- 36. Weingarten A. S.; Kazantsev R. V.; Palmer L. C.; McClendon M.; Koltonow A. R.; Samuel A. P. S.; Kiebala D. J.; Wasielewski M. R.; Stupp S. I.Self-Assembling Hydrogel Scaffolds for Photocatalytic Hydrogen Production.Nat. Chem.2014, 6, 964–970. Google Scholar
- 37. Weingarten A. S.; Kazantsev R. V.; Palmer L. C.; Fairfield D. J.; Koltonow A. R.; Stupp S. I.Supramolecular Packing Controls H2 Photocatalysis in Chromophore Amphiphile Hydrogels.J. Am. Chem. Soc.2015, 137, 15241–15246. Google Scholar
- 38. Guo S.; Chen K. K.; Dong R.; Zhang Z. M.; Zhao J. Z.; Lu T. B.Robust and Long-Lived Excited State Ru(II) Polyimine Photosensitizers Boost Hydrogen Production.ACS Catal.2018, 8, 8659–8670. Google Scholar
- 39. Gross M. A.; Reynal A.; Durrant J. R.; Reisner E.Versatile Photocatalytic Systems for H2 Generation in Water Based on an Efficient DuBois-Type Nickel Catalyst.J. Am. Chem. Soc.2014, 136, 356–366. Google Scholar
- 40. Probst B.; Kolano C.; Hamm P.; Alberto R.An Efficient Homogeneous Intermolecular Rhenium-Based Photocatalytic System for the Production of H2.Inorg. Chem.2009, 48, 1836–1843. Google Scholar
- 41. Takizawa S.; Perez-Bolivar C.; Anzenbacher P.; Murata S.Cationic Iridium Complexes Coordinated with Coumarin Dyes—Sensitizers for Visible-Light-Driven Hydrogen Generation.Eur. J. Inorg. Chem.2012, 2012, 3975–3979. Google Scholar
- 42. Sun J. F.; Zhong F. F.; Yi X. Y.; Zhao J. Z.Efficient Enhancement of the Visible-Light Absorption of Cyclometalated Ir(III) Complexes Triplet Photosensitizers with Bodipy and Applications in Photooxidation and Triplet Triplet Annihilation Upconversion.Inorg. Chem.2013, 52, 6299–6310. Google Scholar
- 43. Guo S.; Ma L. H.; Zhao J. Z.; Kucukoz B.; Karatay A.; Hayvali M.; Yaglioglu H. G.; Elmali A.BODIPY Triads Triplet Photosensitizers Enhanced with Intramolecular Resonance Energy Transfer (RET): Broadband Visible Light Absorption and Application in Photooxidation.Chem. Sci.2014, 5, 489–500. Google Scholar
- 44. Zheng B.; Sabatini R. P.; Fu W. F.; Eum M. S.; Brennessel W. W.; Wang L. D.; McCamant D. W.; Eisenberg R.Light-Driven Generation of Hydrogen: New Chromophore Dyads for Increased Activity Based on Bodipy Dye and Pt(diimine)(dithiolate) Complexes.Proc. Natl. Acad. Sci. U. S. A.2015, 112, 3987–3996. Google Scholar
- 45. Sabatini R. P.; Lindley B.; McCormick T. M.; Lazarides T.; Brennessel W. W.; McCamant D. W.; Eisenberg R.Efficient Bimolecular Mechanism of Photochemical Hydrogen Production Using Halogenated Boron-Dipyrromethene (Bodipy) Dyes and a Bis(dimethylglyoxime) Cobalt(III) Complex.J. Phys. Chem. B2016, 120, 527–534. Google Scholar
- 46. Li G. C.; Mark M. F.; Lv H.; McCamant D. W.; Eisenberg R.Rhodamine-Platinum Diimine Dithiolate Complex Dyads as Efficient and Robust Photosensitizers for Light-Driven Aqueous Proton Reduction to Hydrogen.J. Am. Chem. Soc.2018, 140, 2575–2586. Google Scholar
- 47. Wang P.; Guo S.; Wang H. J.; Chen K. K.; Zhang N.; Zhang Z. M.; Lu T. B.A Broadband and Strong Visible-Light-Absorbing Photosensitizer Boosts Hydrogen Evolution.Nat. Commun.2019, 10, 1–12. Google Scholar
- 48. Clemente-Juan J. M.; Coronado E.; Galan-Mascaros J. R.; Gomez-Garcia C. J.Increasing the Nuclearity of Magnetic Polyoxometalates. Syntheses, Structures, and Magnetic Properties of Salts of the Heteropoly Complexes [Ni3(H2O)3(PW10O39)H2O]7−, [Ni4(H2O)2(PW9O34)2]10−, and [Ni9(OH)3(H2O)6(HPO4)2(PW9O34)3]16−.Inorg. Chem.1999, 38, 55–63. Google Scholar
- 49. Majewski M. B.; Smith J. G.; Wolf M. O.; Patrick B. O.Long-Lived, Emissive Excited States in Direct and Amide-Linked Thienyl-Substituted RuII Complexes.Eur. J. Inorg. Chem.2016, 2016, 1470–1479. Google Scholar
- 50. Takizawa S. Y.; Ikuta N.; Zeng F. Y.; Komaru S.; Sebata S.; Murata S.Impact of Substituents on Excited-State and Photosensitizing Properties in Cationic Iridium(III) Complexes with Ligands of Coumarin 6.Inorg. Chem.2016, 55, 8723–8735. Google Scholar
- 51. PROTEUM2. Version 2. Bruker AXS, Inc.: Madison, WI, 2006. Google Scholar
- 52. Sheldrick G. M.SHELX-97 1997. University of Göttingen: Germany, 1997. Google Scholar
- 53. Banik D.; Bhattacharya S.; Datta P. K.; Sarkar N.Anomalous Dynamics in tert-Butyl Alcohol–Water and Trimethylamine N-Oxide–Water Binary Mixtures: A Femtosecond Transient Absorption Study.ACS Omega2018, 3, 383–392. Google Scholar