Overall reaction mechanism of photocatalytic CO2 reduction on a Re(i)-complex catalyst unit of a Ru(ii)-Re(i) supramolecular photocatalyst.

Rhenium(i) complexes fac-[ReI(diimine)(CO)3(L)]n+ are mostly used and evaluated as photocatalysts and catalysts in both photochemical and electrochemical systems for CO2 reduction. However, the selective reduction mechanism of CO2 to CO is unclear, although numerous mechanistic studies have been reported. A Ru(ii)-Re(i) supramolecular photocatalyst with fac-[ReI(diimine)(CO)3{OC(O)OCH2CH2NR2}] (R = C2H4OH) as a catalyst unit (RuC2Re) exhibits very high efficiency, selectivity, and durability of CO formation in photocatalytic CO2 reduction reactions. In this work, the reaction mechanism of photocatalytic CO2 reduction using RuC2Re is fully clarified. Time-resolved IR (TR-IR) measurements using rapid-scan FT-IR spectroscopy with laser flash photolysis verify the formation of RuC2Re(COOH) with a carboxylic acid unit, i.e., fac-[ReI(diimine)(CO)3(COOH)], in the photocatalytic reaction solution. Additionally, this important intermediate is detected in an actual photocatalytic reaction using steady state irradiation. Kinetics analysis of the TR-IR spectra and DFT calculations demonstrated the reaction mechanism of the conversion of the one-electron reduced species of RuC2Re with a fac-[ReI(diimine˙-)(CO)3{OC(O)OCH2CH2NR2}]- unit, which was produced via the photochemical reduction of RuC2Re by 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), to RuC2Re(COOH). The kinetics of the recovery processes of the starting complex RuC2Re from RuC2Re(COOH) accompanying the release of CO and OH- was also clarified. As a side reaction of RuC2Re(COOH), a long-lived carboxylate-ester complex with a fac-[ReI(diimine)(CO)3(COOC2H4NR2)] unit, which was produced by the nucleophilic attack of TEOA to one of the carbonyl ligands of RuC2Re(CO) with a fac-[ReI(diimine)(CO)4]+ unit, was formed during the photocatalytic reaction. This complex works not only as a precursor in another minor CO formation process but also as an external photosensitiser that photochemically reduces the other complexes i.e., RuC2Re, RuC2Re(COOH), and the intermediate that is reductively converted to RuC2Re(COOH).

Sodium-Glucose Cotransporter-2 Inhibitors Stabilize Coronary Plaques in Acute Coronary Syndrome With Diabetes Mellitus.

Sodium-glucose cotransporter-2 inhibitors (SGLT2is) are widely used in cardiology and are effective in treating acute coronary syndrome (ACS). Their effects on unstable plaque in patients with ACS remains unclear. This study aimed to examine the effectiveness of SGLT2is in coronary plaque based on optical coherence tomography (OCT) images and the prognosis of ACS with type 2 diabetes mellitus. This retrospective study included 109 patients in the total cohort and 29 patients in the OCT cohort. Based on SGLT2i administration after ACS, the total cohort was categorized into non-SGLT2i (n = 69) and SGLT2i (n = 40) groups. The OCT cohort had 15 and 14 patients in the non-SGLT2i and SGLT2i groups, respectively. The OCT images of unstable plaque were analyzed in nonstented lesions during ACS catheterization and at the 6-month follow-up. The total cohort was assessed after 1 year for major adverse cardiovascular events, including all-cause mortality, revascularization, cerebrovascular disease, and heart failure hospitalization. SGLT2is improved unstable lesions with a significantly thicker fibrous cap (48 ± 15 µm vs 26 ± 24 µm, p = 0.005), reduced lipid arc (-29 ± 12° vs -18 ± 14°, p = 0.028), higher % decrease in total lipid arc (-35 ± 13% vs -19 ± 18%, p = 0.01), and lower major adverse cardiovascular event incidence (log-rank p = 0.023, hazard ratio 4.72 [1.08 to 20.63]) and revascularization rate (adjusted hazard ratio 6.77 [1.08 to 42.52]) than the non-SGLT2i group. In conclusion, SGLT2is can improve the markers of plaque stability and may improve the prognosis in patients with type 2 diabetes mellitus.

Incidence, clinical course, and risk factors in the development of femoral pseudoaneurysm after atrial fibrillation ablation.

Background: Previous studies have revealed the risk factors for femoral pseudoaneurysms (FPA). Most data on FPA are based on coronary and peripheral interventions, with limited studies focusing on atrial fibrillation (AF) ablation. However, patient backgrounds, anticoagulation regimens, and vascular access methods differ. In addition, a standard for managing FPA after AF ablation remains elusive due to the difficult nature of achieving thrombosis in pseudoaneurysms. Methods: This single-center, retrospective, observational study included 2805 consecutive patients who underwent AF ablation between January 2016 and December 2021. All patients underwent femoral artery and vein punctures. Puncture sites were checked 1 day post-procedure. Results: A total of 23 FPA patients were identified during the study period. Multivariate logistic regression analysis showed that hypertension (odds ratio 4.66, 95% confidence interval: 1.38-15.71; p = .0032) and warfarin use (odds ratio 3.83, 95% confidence interval: 1.40-10.45; p = .021) were significantly associated with the occurrence of FPA. The compression success rate was low (22%). There were nine and six patients in the endovascular treatment (EVT) and ultrasound-guided thrombin injection (UGTI) groups, respectively. The success rates were 100% and 84% in the EVT and UGTI groups, respectively. The length of hospital stay after FPA treatment was 2.1 days in the EVT group and 1.3 days in the thrombin group. Conclusion: We must be careful about post-procedural FPA, especially for hypertension and warfarin-using patients. Treatment of pseudoaneurysms with anticoagulants is unlikely to achieve hemostasis, and an early switch to invasive treatments, such as EVT, should be considered.

Correction to "Highly Efficient Supramolecular Photocatalyst for CO2 Reduction with Eight Carbon-Carbon Bonds between Ru(II) Photosensitizer and Re(I) Catalyst Unit".

[This corrects the article DOI: 10.1021/acscatal.3c01407.].

Selective electrochemical CO2 conversion with a hybrid polyoxometalate.

A multi-component coordination compound, in which ruthenium antenna complexes are connected to a polyoxotungstate core is presented. This hybrid cluster effectively promotes the electrochemical conversion of CO2 to C1 feedstocks, the selectivity of which can be controlled by the acidity of the media.

Photocatalyzed CO2 reduction to CO by supramolecular photocatalysts made of Ru(II) photosensitizers and Re(I) catalytic subunits containing preformed CO2TEOA adducts.

Two new supramolecular photocatalysts containing Ru(II) polypyridine units as light-harvesting photosensitizers and Re(I) polypyridine subunits as catalytic centers have been prepared. The new species, RuRe2A and Ru2ReA, contain catalytic Re(I) subunits coordinated by the preformed CO2TEOA adduct (known to be the effective catalytic subunits; TEOA is triethanolamine) and exhibit quite efficient and selective photoreduction of CO2 to CO, with outstanding TONs of 2368 and 2695 and a selectivity of 99.9% and 98.9%, respectively. Such photocatalytic properties are significantly improved with respect to those of previously studied RuRe2 and Ru2Re parent compounds, containing chloride ligands instead of the CO2TEOA adduct. Comparison between photocatalytic performance of the new species and their parent compounds allows to investigate the effect of the CO2TEOA insertion process as well as the eventual effect of the presence of chloride ions in solution on the photocatalytic processes. The improved photocatalytic properties of RuRe2A and Ru2ReA compared with their parent species are attributed to a combined effect of different distribution of the one-electron reduced form of the supramolecular photocatalysts on the Ru-subunit(s) (leading to decreased CO formation due to a poisoning ligand loss process) and on the Re-subunit(s) and to the presence of chloride ions in solution for RuRe2 and Ru2Re, which could interfere with the CO2TEOA adduct formation, a needed requisite for CO forming catalysis. These results strongly indicate the utility of preparing supramolecular photocatalysts containing preformed adducts.

A case of chronic total occlusion in popliteal artery recanalized by double snare piercing technique.

BACKGROUND: Although majority of cases with chronic total occlusion (CTO) in femoro-popliteal lesion were treated with antegrade approach only, some lesions require alternative approach due to its complexity. Bi-directional approach is useful on endovascular therapy (EVT) for CTO; however guidewire passage through the lesion is impossible in some challenging cases. The present case shows a successful re-entry technique utilizing two snare catheters from an antegrade and retrograde access site (double snare piecing technique). CASE PRESENTATION: A 79-year-old woman with right leg intermittent claudication (Rutherford category IV), who had undergone unsuccessful EVT for popliteal CTO, required another EVT for the worsening symptom. Following the failed conventional crossing technique (wire knuckle technique, intravascular-ultrasound-guided wiring, and controlled antegrade and retrograde subintimal tracking technique), two snare catheters were placed and the snare loops were pierced by a puncture needle percutaneously. After an 0.014 wire was inserted into the needle, the needle was withdrawn. The wire was pulled from the retrograde side and was externalized. Then, the antegrade snare catheter was pulled and externalized, to make the wire across the lesion. After that, a microcatheter was advanced along the externalized wire from the retrograde side and cross the lesion. The wire was replaced with a new wire, which completely created pull-through system. After the hemostasis by balloon inflation and lesion preparation, this procedure was completed with an endoluminal-covered stent and two inter-woven stents. The re-entry site was covered by the inter-woven stent. Her symptoms improved after the procedure, and the lesion has not developed restenosis at 2-years follow-up. CONCLUSIONS: This re-entry technique of puncturing two snare loops (double snare piercing technique) might be effective for achieving successful passage through challenging femoropopliteal CTO cases.

Surface-Specific Modification of Graphitic Carbon Nitride by Plasma for Enhanced Durability and Selectivity of Photocatalytic CO2 Reduction with a Supramolecular Photocatalyst.

Photocatalytic CO2 reduction is in high demand for sustainable energy management. Hybrid photocatalysts combining semiconductors with supramolecular photocatalysts represent a powerful strategy for constructing visible-light-driven CO2 reduction systems with strong oxidation power. Here, we demonstrate the novel effects of plasma surface modification of graphitic carbon nitride (C3N4), which is an organic semiconductor, to achieve better affinity and electron transfer at the interface of a hybrid photocatalyst consisting of C3N4 and a Ru(II)-Ru(II) binuclear complex (RuRu'). This plasma treatment enabled the "surface-specific" introduction of oxygen functional groups via the formation of a carbon layer, which worked as active sites for adsorbing metal-complex molecules with methyl phosphonic-acid anchoring groups onto the plasma-modified surface of C3N4. Upon photocatalytic CO2 reduction with the hybrid under visible-light irradiation, the plasma-surface-modified C3N4 with RuRu' enhanced the durability of HCOOH production by three times compared to that achieved when using a nonmodified system. The high selectivity of HCOOH production against byproduct evolution (H2 and CO) was improved, and the turnover number of HCOOH production based on the RuRu' used reached 50 000, which is the highest among the metal-complex/semiconductor hybrid systems reported thus far. The improved activity is mainly attributed to the promotion of electron transfer from C3N4 to RuRu' under light irradiation via the accumulation of electrons trapped in deep defect sites on the plasma-modified surface of C3N4.

Supramolecular multi-electron redox photosensitisers comprising a ring-shaped Re(i) tetranuclear complex and a polyoxometalate.

Redox photosensitisers (PSs) play essential roles in various photocatalytic reactions. Herein, we synthesised new redox PSs of 1 : 1 supramolecules that comprise a ring-shaped Re(i) tetranuclear complex with 4+ charges and a Keggin-type heteropolyoxometalate with 4- charges. These PSs photochemically accumulate multi-electrons in one molecule (three or four electrons) in the presence of an electron donor and can supply electrons with different reduction potentials. PSs were successfully applied in the photocatalytic reduction of CO2 using catalysts (Ru(ii) and Re(i) complexes) and triethanolamine as a reductant. In photocatalytic reactions, these supramolecular PSs supply a different number of electrons to the catalyst depending on the redox potential of the intermediate, which is made from the one-electron-reduced species of the catalyst and CO2. Based on these data, information on the reduction potentials of the intermediates was obtained.

Photocatalytic Systems for CO2 Reduction: Metal-Complex Photocatalysts and Their Hybrids with Photofunctional Solid Materials.

ConspectusPhotocatalytic CO2 reduction is a critical objective in the field of artificial photosynthesis because it can potentially make a total solution for global warming and shortage of energy and carbon resources. We have successfully developed various highly efficient, stable, and selective photocatalytic systems for CO2 reduction using transition metal complexes as both photosensitizers and catalysts. The molecular architectures for constructing selective and efficient photocatalytic systems for CO2 reduction are discussed herein. As a typical example, a mixed system of a ring-shaped Re(I) trinuclear complex as a photosensitizer and fac-[Re(bpy)(CO)3{OC2H4N(C2H4OH)2}] as a catalyst selectively photocatalyzed CO2 reduction to CO with the highest quantum yield of 82% and a turnover number (TON) of over 600. Not only rare and noble metals but also earth abundant ones, such as Mn(I), Cu(I), and Fe(II) can be used as central metal cations. In the case using a Cu(I) dinuclear complex as a photosensitizer and fac-Mn(bpy)(CO)3Br as a catalyst, the total formation quantum yield of CO and HCOOH from CO2 was 57% and TONCO+HCOOH exceeded 1300.Efficient supramolecular photocatalysts for CO2 reduction, in which photosensitizer and catalyst units are connected through a bridging ligand, were developed for removing a diffusion control on collisions between a photosensitizer and a catalyst. Supramolecular photocatalysts, in which [Ru(N∧N)3]2+-type photosensitizer and Re(I) or Ru(II) catalyst units are connected to each other with an alkyl chain, efficiently and selectively photocatalyzed CO2 reduction in solutions. Mechanistic studies using time-resolved IR and electrochemical measurements provided molecular architecture for constructing efficient supramolecular photocatalysts. A Ru(II)-Re(I) supramolecular photocatalyst constructed according to this molecular architecture efficiently photocatalyzed CO2 reduction even when it was fixed on solid materials. Harnessing this property of the supramolecular photocatalysts, two types of hybrid photocatalytic systems were developed, namely, photocatalysts with light-harvesting capabilities and photoelectrochemical systems for CO2 reduction.Introduction of light-harvesting capabilities into molecular photocatalytic systems should be important because the intensity of solar light shone on the earth's surface is relatively low. Periodic mesoporous organosilica, in which methyl acridone groups are embedded in the silica framework as light harvesters, was combined with a Ru(II)-Re(I) supramolecular photocatalyst with phosphonic acid anchoring groups. In this hybrid, the photons absorbed by approximately 40 methyl acridone groups were transferred to one Ru(II) photosensitizer unit, and then, the photocatalytic CO2 reduction commenced.To use water as an abundant electron donor, we developed hybrid photocatalytic systems combining metal-complex photocatalysts with semiconductor photocatalysts that display high photooxidation powers, in which two photons are sequentially absorbed by the metal-complex photosensitizer and the semiconductor, resulting in both high oxidation and reduction power. Various types of dye-sensitized molecular photocathodes comprising the p-type semiconductor electrodes and the supramolecular photocatalysts were developed. Full photoelectrochemical cells combining these dye-sensitized molecular photocathodes and n-type semiconductor photoanodes achieved CO2 reduction using only visible light as the energy source and water as the reductant. Drastic improvement of dye-sensitized molecular photocathodes is reported.The results presented in this Account clearly indicate that we can construct very efficient, selective, and durable photocatalytic systems constructed with the metal-complex photosensitizers and catalysts. The supramolecular-photocatalyst architecture in which the photosensitizer and the catalyst are connected to each other is useful especially on the surface of solid owing to rapid electron transfer from the photosensitizer to the catalyst. On basis of these findings, we successfully constructed hybrid systems of the supramolecular photocatalysts with photoactive solid materials. These hybridizations can add new functions to the metal-complex photocatalytic systems, such as water oxidation and light harvesting.

Coronary Access After TAVR With a Cylindrical-Shaped Valve: Learning From LOTUS.

BACKGROUND/PURPOSE: Data on the feasibility of coronary access (CA) through above or outside of the cylindrical shaped-transcatheter heart valve (THV) are very limited. The aims of the present study were to assess the feasibility of CA after transcatheter aortic valve replacement (TAVR) with the LOTUS using multi detector computed tomography (MDCT) and the reliability of algorithm detecting unfavorable CA. METHODS/MATERIALS: Post-TAVR MDCT of 41 patients with 82 coronary arteries were evaluated. The relationship and distance between the THV flame and sinotubular junction (STJ) and coronary ostia were assessed. Unfavorable CA was defined as the valve-to-STJ distance < 2-mm or the valve-to-coronary ostia distance < 2-mm if the THV flame was above STJ or coronary ostia. RESULTS: MDCT-identified unfavorable CA was observed in 29.3% for the left coronary artery and 41.5% for the right coronary artery. In total, 53.7% of patients had at least one unfavorable CA and 14.6% of those had unfavorable CA for both left and right coronary artery. While patients underwent coronary angiography after TAVR, the success rates of selective coronary cannulation were significantly lower in patients with MDCT-identified unfavorable CA in comparison to those with favorable CA for left (20.0% vs. 100%, P = 0.002) and right coronary artery (0% vs. 100%, P < 0.001). CONCLUSIONS: Future CA through above or outside of a cylindrical shaped THV may be challenging with a significant probability. Our algorithm identifying unfavorable CA using post-MDCT seems to be useful for estimating the risk of unsuccessful selective cannulation.

Development of a panchromatic photosensitizer and its application to photocatalytic CO2 reduction.

We designed and synthesized a heteroleptic osmium(ii) complex with two different tridentate ligands, Os. Os can absorb the full wavelength range of visible light owing to S-T transitions, and this was supported by TD-DFT calculations. Excitation of Os using visible light of any wavelength generates the same lowest triplet metal-to-ligand charge-transfer excited state, the lifetime of which is relatively long (τ em = 40 ns). Since excited Os could be reductively quenched by 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole, Os displays high potential as a panchromatic photosensitizer. Using a combination of Os and a ruthenium(ii) catalyst, CO2 was photocatalytically reduced to HCOOH via irradiation with 725 nm light, and the turnover number reached 81; irradiation with light at λ ex > 770 nm also photocatalytically induced HCOOH formation. These results clearly indicate that Os can function as a panchromatic redox photosensitizer.

Mechanistic study of photocatalytic CO2 reduction using a Ru(ii)-Re(i) supramolecular photocatalyst.

Supramolecular photocatalysts comprising [Ru(diimine)3]2+ photosensitiser and fac-[Re(diimine)(CO)3{OC(O)OC2H4NR2}] catalyst units can be used to reduce CO2 to CO with high selectivity, durability and efficiency. In the presence of triethanolamine, the Re catalyst unit efficiently takes up CO2 to form a carbonate ester complex, and then direct photocatalytic reduction of a low concentration of CO2, e.g., 10% CO2, can be achieved using this type of supramolecular photocatalyst. In this work, the mechanism of the photocatalytic reduction of CO2 was investigated applying such a supramolecular photocatalyst, RuC2Re with a carbonate ester ligand, using time-resolved visible and infrared spectroscopies and electrochemical methods. Using time-resolved spectroscopic measurements, the kinetics of the photochemical formation processes of the one-electron-reduced species RuC2(Re)-, which is an essential intermediate in the photocatalytic reaction, were clarified in detail and its electronic structure was elucidated. These studies also showed that RuC2(Re)- is stable for 10 ms in the reaction solution. Cyclic voltammograms measured at various scan rates besides temperature and kinetic analyses of RuC2(Re)- produced by steady-state irradiation indicated that the subsequent reaction of RuC2(Re)- proceeds with an observed first-order rate constant of approximately 1.8 s-1 at 298 K and is a unimolecular reaction, independent of the concentrations of both CO2 and RuC2(Re)-.

Early onset bioprosthetic tricuspid valve stenosis in a case with cardiac sarcoidosis: Pathological findings based on autopsy.

A 60-year-old woman with cardiac sarcoidosis developed recurrent and refractory right heart failure 26 months after tricuspid valve replacement. Echocardiography revealed thickened and immobile cusp with increased diastolic tricuspid gradient of 8-10 mmHg, consistent with bioprosthetic tricuspid stenosis (TS). Prolonged intravenous injection of dobutamine and carperitide, with intermittent intravenous furosemide, was necessary at multiple times. Despite treatment, the patient died of refractory right heart failure. The explanted tricuspid bioprosthesis on autopsy revealed marked pannus formation, resulting in stiff and immobile cusps while the same mitral bioprosthesis, which was implanted on the same day, was normal. Sarcoid granulomas were not present either in tricuspid or mitral bioprostheses. Chronic valve inflammation associated with prolonged use of intravenous drugs and multiple episodes of line-associated bacteremia may have caused early onset bioprosthetic TS. Learning objectives:1Early onset bioprosthetic tricuspid stenosis (TS) is rare.2Elevated jugular venous pulse and pan-diastolic rumble with the Rivero-Carvallo sign are keys to the diagnosis of TS which is confirmed using echocardiography.3Repeated episodes of bacteremia associated with prolonged infusion of intravenous drugs might have contributed to the development of early onset bioprosthetic TS.

Photocatalysis of a Dinuclear Ru(II)-Re(I) Complex for CO2 Reduction on a Solid Surface.

The development of CO2-reduction photocatalysts is one of the main targets in the field of artificial photosynthesis. Recently, numerous hybrid systems in which supramolecular photocatalysts comprised of a photosensitizer and catalytic-metal-complex units are immobilized on inorganic solid materials, such as semiconductors or mesoporous organosilica, have been reported as CO2-reduction photocatalysts for various functions, including water oxidation and light harvesting. In the present study, we investigated the photocatalytic properties of supramolecular photocatalysts comprised of a Ru(II)-complex photosensitizer and a Re(I)-complex catalyst fixed on the surface of insulating Al2O3 particles: the distance among the supramolecular photocatalyst molecules should be fixed. Visible-light irradiation of the photocatalyst in the presence of an electron donor under a CO2 atmosphere produced CO selectively. Although CO formation was also observed for a 1:1 mixture of mononuclear Ru(II) and Re(I) complexes attached to an Al2O3 surface, the photocatalytic activity was much lower. The activity of the Al2O3-supported photocatalyst was strongly dependent on the adsorption density of the supramolecular moiety, where the initial rate of photocatalytic CO formation was faster at lower density and higher photocatalyst durability was achieved at higher density. One of the main reasons for the former phenomenon is the decreased quenching fraction of the excited state of the photosensitizer unit by the reductant dissolved in the solution phase in the case of higher density. This is due to the self-quenching of the excited photosensitizer unit and steric hindrance between the condensed supramolecular photocatalyst molecules attached to the surface. The higher durability of the more condensed system is caused by intermolecular electron transfer between reduced supramolecular photocatalyst molecules, which accelerates the formation of CO in the photocatalytic CO2 reduction. Coadsorption of a Ru(II) mononuclear complex as a redox photosensitizer could drastically reinforce the photocatalysis of the supramolecular photocatalyst on the surface of the Al2O3 particles: more than 10 times higher turnover number and about 3.4 times higher turnover frequency of CO formation. These investigations provide new architectures for the construction of efficient and durable hybrid photocatalytic systems for CO2 reduction, which are composed of metal-complex photocatalysts and solid materials.

Factors determining formation efficiencies of one-electron-reduced species of redox photosensitizers.

Improvement in the photochemical formation efficiency of one-electron-reduced species (OERS) of a photoredox photosensitizer (a redox catalyst) is directly linked to the improvement in efficiencies of the various photocatalytic reactions themselves. We investigated the primary processes of a photochemical reduction of two series [Ru(diimine)3]2+ and [Os(diimine)3]2+ as frequently used redox photosensitizers (PS2+), by 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as a typical reductant in detail using steady-irradiation and time-resolved spectroscopies. The rate constants of all elementary processes of the photochemical reduction of PS2+ by BIH to give the free PS•+ were obtained or estimated. The most important process for determining the formation efficiency of the free PS•+ was the escape yield from the solvated ion pair [PS•+-BIH•+], which was strongly dependent on both the central metal ion and the ligands. In cases with the same central metal ion, the system with larger -ΔGbet, which is the free energy change in the back-electron transfer from the OERS of PS•+ to BIH•+, tended to lower the escape yield of the free OERS of PS2+. On the other hand, different central metal ions drastically affected the escape yield even in cases with similar -ΔGbet; the escape yield in the case of RuH2+ (-ΔGbet = 1.68 eV) was 5-11 times higher compared to those of OsH2+ (-ΔGbet = 1.60 eV) and OsMe2+ (-ΔGbet = 1.71 eV). The back-electron transfer process from the free PS•+ to the free BIH•+ could not compete against the further reaction of the free BIH•+, which is the deprotonation process giving BI•, in DMA for all examples. The produced BI• gave one electron to PS2+ in the ground state to give another PS•+, quantitatively. Based on these findings and investigations, it is clarified that the photochemical formation efficiency of the free PS•+ should be affected not only by -ΔGbet but also by the heavy-atom effect of the central metal ion, and/or the oxidation power of the excited PS2+, which should determine the distance between the excited PS and BIH at the moment of the electron transfer.

Efficient trinuclear Ru(ii)-Re(i) supramolecular photocatalysts for CO2 reduction based on a new tris-chelating bridging ligand built around a central aromatic ring.

We have designed and synthesized a new tris-chelating polypyridine ligand (bpy3Ph) suitable to be used as a bridging ligand (BL) for constructing various supramolecular photocatalysts. This BL is a phenylene ring with three ethylene chains at 1, 3, and 5 positions, of which the other terminals are connected to 2,2'-bipyridine moieties. The ligand bpy3Ph has been used to prepare, according to a multi-step synthetic protocol, trinuclear supramolecular photocatalysts containing different metal subunits. In particular, the compounds Ru2Re and RuRe2 have been prepared, containing different ratios of components based on Ru(dmb)3 2+-type and Re(dmb)(CO)3Cl-type units (dmb = 4,4'-dimethyl-2,2'-bipyridine), which can play the roles of photosensitizers and catalyst units for photocatalytic CO2 reduction, respectively. The trinuclear model Ru3 and mononuclear and dinuclear Ru and Ru2 precursor metal complexes, containing free chelating sites, have also been synthesized using the same bridging ligand. The absorption spectra, redox behaviour and photophysical properties of the new species indicate that there is no strong electronic interaction among the Ru and Re units. The trinuclear complexes Ru2Re and RuRe2 could photocatalyze CO2 reduction to CO with high selectivity (up to 97%), high efficiency (Φ COs of 28% and 25%, respectively: BIH as a reductant), and high durability (TONCOs of 5232 and 6038, respectively: BIH as a reductant) which are the largest TONs for CO2 reduction using supramolecular photocatalysts in homogeneous solutions. The absence of negligible accumulation of the mono-reduced form of the photosensitizer indicates fast electron transfer to the catalyst unit(s) through the relatively large bridging ligand and is proposed to contribute to the outstanding photocatalytic properties of the new species, including their durability. The relevant photocatalytic behaviour of the new systems indicates new avenues for the design of extended bridging ligands capable of efficiently and functionally integrating photosensitizers and catalysts towards the preparation of new, larger supramolecular photocatalysts for selective CO2 reduction.