A Small Organic Molecular Catalyst with Efficient Electron Accumulation for Near-unity CO2 Photoreduction.

Molecular catalysis is of great interest to CO2 photoreduction. Various transition metal complexes have been developed as efficient molecular catalysts. However, it remains a challenge to catalyze CO2 reduction by a small organic molecular photocatalyst, as the accumulation of multiple electrons in a small organic molecule is normally difficult for CO2 reduction. We report herein a small organic molecular catalyst can be used for selective reduction of CO2 to CO under visible light irradiation. The turnover number (TON) of CO formation is found to be 400±26 with near 100% selectivity in DMF/H2 O medium. UV-Vis absorption spectroscopy, density functional theory (DFT) calculations, and spectroelectrochemical studies demonstrate that the organic molecular catalyst is capable of accumulating electrons through a 2e- reduced product which shows good stability and is responsible for interacting with CO2 . These findings elucidate an accessible way to develop purely organic molecular catalysts for CO2 reduction by strengthening the electron accumulation.

Exploiting consecutive photoinduced electron transfer (ConPET) in CO2 photoreduction.

The consecutive photoinduced electron transfer (ConPET) process of 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) in CO2 photoreduction to achieve powerful reducing species has been disclosed by activating a bis(terpyridine)ruthenium(II) complex bearing a high overpotential for selective light-driven reduction of CO2 to CO in homogeneous solution.

Noble metal-free bis-tridentate benzimidazole zinc(II) and iron(II) complexes for selective CO2 photoreduction.

Three noble metal-free metal complexes [Fe(Me-bzimpy)2]2+ (Fe1), [Fe(bzimpy)2]2+ (Fe2) and [Zn(Me-bzimpy)2]2+ (Zn1) were synthesized and studied in the visible light-driven CO2 reduction, where ligands bzimpy and Me-bzimpy were 2,6-bis(1-methyl-1H-benzo[d]imidazol-2-yl)pyridine and 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine, respectively. It was found that Fe1 displayed the best photocatalytic performance with a turnover number (TON) of 878 and high selectivity up to 99.2% towards CO generation in the presence of an organic thermally activated delayed fluorescence (TADF) photosensitizer, which was more than 10 times that of Fe2 (TONCO = 63) and Zn1 (TONCO = 53). This is attributed to the much higher stability of Fe1 upon reduction, as proved by the cyclic voltammograms of the three complexes. These results highlight the cooperation of ligands and metals in molecular metal complexes for CO2 photoreduction.

Coordination-driven discrete metallo-supramolecular assembly for rapid and selective photochemical CO2 reduction in aqueous solution.

A discrete metallo-supramolecular assembly composed of six iron(ii) cations and twelve redox-active terpyridine fragments has been developed for the highly efficient visible-light-driven reduction of CO2 to CO with a TON of 14 956 and 99.6% selectivity in the presence of an organic thermally activated delayed fluorescence (TADF) photosensitizer 4CzIPN in aqueous solution. The photochemical system proceeds rapidly with a turnover frequency (TOF) of 276 min-1. It is demonstrated that the redox-active terpyridine fragments in the assembly are reduced by the photosensitizer which could further act as an electron reservoir for CO2 reduction, resulting in the highly efficient reduction of CO2. This work shows that discrete metallo-supramolecular assemblies could be used for robust photochemical CO2 reduction.

Water-Assisted Highly Efficient Photocatalytic Reduction of CO2 to CO with Noble Metal-Free Bis(terpyridine)iron(II) Complexes and an Organic Photosensitizer.

Photocatalytic CO2 reduction reaction is believed to be a promising approach for CO2 utilization. In this work, a noble metal-free photocatalytic system, composed of bis(terpyridine)iron(II) complexes and an organic thermally activated delayed fluorescence compound, has been developed for selective reduction of CO2 to CO with a maximum turnover number up to 6320, 99.4% selectivity, and turnover frequency of 127 min-1 under visible-light irradiation in dimethylformamide/H2O solution. More than 0.3 mmol CO was generated using 0.05 µmol catalyst after 2 h of light irradiation. The apparent quantum yield was found to be 9.5% at 440 nm (180 mW cm-2). Control experiments and UV-vis-NIR spectroscopy studies further demonstrated that water strongly promoted the photocatalytic cycle and terpyridine ligands rather than Fe(II) were initially reduced during the photocatalytic process.

Merging an organic TADF photosensitizer and a simple terpyridine-Fe(iii) complex for photocatalytic CO2 reduction.

An earth-abundant photocatalytic system composed of an organic TADF photosensitizer and a simple terpyridine-Fe(iii) complex was developed for CO2 reduction. In the presence of water, significant enhancement of CO generation was observed with 99.3% selectivity. The turnover number (TON) and turnover frequency (TOF) were determined to be 2250 and 60 min-1, respectively.

A long-lived Donor-Acceptor fluorescent probe for sequential detection of Cu2+ and biothiols.

A new long-lived Donor-Acceptor (D-A) fluorophore based on carbazolyl dicyanobenzene was developed as an ON-OFF-ON multifunctional fluorescent probe 1 for sequential detection of Cu2+ and biothiols (Cys, Hcy and GSH). The fluorescence of probe 1 can be significantly and selectively quenched by Cu2+. Meanwhile, the fluorescence lifetime decreased from 2.1 µs to 18.5 ns. The limit of detection was determined to be 33.6 nM. Upon addition of biothiols (Cys, Hcy and GSH), the generated ensemble 1-Cu2+ displayed a "turn-on" fluorescent response at 555 nm and an obvious recovery in fluorescence lifetime and UV-vis absorption within 1 min. The limit of detection for Cys, Hcy and GSH were calculated by fluorescence titration experiments to be 0.19, 0.21 and 0.29 µM, respectively. The ensemble 1-Cu2+ was further successfully applied in bioimaging.

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 is composed of an organic thermally activated delayed fluorescence (TADF) chromophore and cobaloximes, has been designed and synthesized for the first time for the efficient acceptorless dehydrogenation of secondary amines under blue light irradiation at room temperature. The TADF chromophore has a long lifetime of 17.4 µs with suitable redox potentials for the selective acceptorless dehydrogenation of secondary amines to afford imines and H2 through cooperative catalysis of the chromophore and cobaloximes in the supramolecular assembly. A high TON of 895 was obtained for the acceptorless dehydrogenation of 1,2,3,4-tetrahydroisoquinoline despite its high oxidation potential (+1.38 V vs. SCE).

Robust Cooperative Photo-oxidation of Sulfides without Sacrificial Reagent under Air Using a Dinuclear RuII -CuII Assembly.

A molecular chromophore-catalyst assembly containing a chromophore ruthenium(II) center (RuIIchro ) and a catalytic copper(II) center (CuIIcat ) has been prepared easily. The assembly was employed for photocatalytic oxidation of sulfides without sacrificial reagent in the presence of dioxygen under blue light irradiation. Unprecedented turnover number (TON) up to 32 000 was achieved. It was elucidated that an electron transferred from excited state of chromophore RuII*chro to CuIIcat along with generation of CuIcat that was further activated by O2 . These results demonstrate a promising strategy for efficient cooperative photocatalytic reactions under air using the chromophore-catalyst assembly.

Nanomolar pyrophosphate detection and nucleus staining in living cells with simple terpyridine-Zn(II) complexes.

Great efforts have been made to develop fluorescent probes for pyrophosphate (PPi) detection. Nucleus staining with fluorescence microscopy has been also widely investigated. But fluorescent probes for PPi detection with high sensitivity in water medium and nucleus staining with low-cost non-precious metal complexes in living cells are still challenging. Herein, we report simple terpyridine-Zn(II) complexes for selective nanomolar PPi detection over ATP and ADP in water based on aggregation induced emission (AIE) and intramolecular charge transfer (ICT). In addition, these terpyridine-Zn(II) complexes were successfully employed for nucleus staining in living cells. These results demonstrated simply obtained terpyridine-Zn(II) complexes are powerful tool for PPi detection and the development of PPi-related studies.

Insight into highly selective photocatalytic oxidation of alcohols by a new trinuclear ruthenium complex with visible light.

A new ligand bearing two tpy moieties and one bpy unit (tpy = 2,2':6',2''-terpyridine; bpy = 2,2'-bipyridine) linked by carbon-carbon single bonds and its corresponding trinuclear ruthenium complex were readily synthesized in high yield, and characterized by (1)H NMR spectroscopy, high-resolution electrospray ionization mass spectrometry (HR-ESI/MS) and elemental analysis. The ruthenium complex exhibited moderate catalytic activity towards selective oxidation of alcohols in water with visible light under an air atmosphere. Investigations of UV/vis spectra, electrochemistry and ESI/MS suggested that the catalytic cycle involves two processes, Ru(c)(II)-OH2/Ru(c)(III)-OH and Ru(c)(III)-OH/Ru(c)(IV)=O. The effective electron transfer from the excited state *[Ru(tpy)2](2+) to [Co(NH3)5Cl]Cl2 is proposed to be responsible for the good activities of this visible-light-driven system under an air atmosphere.

Facile synthesis of a ruthenium assembly and its application for light-driven oxidation of alcohols in water.

A supramolecular assembly containing two light harvesting fragments [Ru(tpy)2](2+) and one catalytic unit [Ru(tpy)(bpy)Cl](+) was synthesized in a facile manner in 90% yield, and exhibited high photocatalytic product-selectivity compared with the corresponding bimolecular system in the light-driven oxidation of alcohols using [Co(NH3)5Cl]Cl2 as a sacrificial oxidant in water at room temperature.