In contrast to previous studies, we disclose for the first time that the singlet excited state ((1)PS*) of BODIPY rather than the triplet excited state ((3)PS*) can drive C-H bond activation to form C-C and C-P bonds smoothly, which offers new methods to promote organic transformation under visible light irradiation.
Nature uses hydrogenase enzyme to catalyze proton reduction at pH 7 with overpotentials and catalytic efficiencies that rival platinum electrodes. Over the past several years, [FeFe]-hydrogenase ([FeFe]-H2 ase) mimics have been demonstrated to be effective catalysts for light-driven H2 evolution. However, it remains a significant challenge to realize H2 production by such an artificial photosynthetic system in neutral aqueous solution. Herein, we report a new system for photocatalytic H2 evolution working in a broad pH range, especially under neutral conditions. This unique system is consisted of branched polyethylenimine (PEI)-grafted [FeFe]-H2 ase mimic (PEI-g-Fe2 S2 ), MPA-CdSe quantum dots (MPA=mercaptopropionic acid), and ascorbic acid (H2 A) in water. Due to the secondary coordination sphere of PEI, which has high buffering capacity and stabilizing ability, the system is able to produce H2 under visible-light irradiation with turnover number of 10 600 based on the Fe2 S2 active site in PEI-g-Fe2 S2 . The stability and activity are much better than that of the same system under acidic or basic conditions and they are, to the best of our knowledge, the highest known to date for photocatalytic H2 evolution from a [FeFe]-H2 ase mimic in neutral aqueous solution.
Direct allylic C−H thiolation is straightforward for allylic C(sp3)−S bond formation. However, strong interactions between thiol and transition metal catalysts lead to deactivation of the catalytic cycle or oxidation of sulfur atom under oxidative condition. Thus, direct allylic C(sp3)−H thiolation has proved difficult. Represented herein is an exceptional for direct, efficient, atom‐ and step‐economic thiolation of allylic C(sp3)−H and thiol S−H under visible light irradiation. Radical trapping experiments and electron paramagnetic resonance (EPR) spectroscopy identified the allylic radical and thiyl radical generated on the surface of photocatalyst quantum dots (QDs). The C−S bond formation does not require external oxidants and radical initiators, and hydrogen (H2) is produced as byproduct. When vinylic C(sp2)−H was used instead of allylic C(sp3)−H bond, the radical‐radical cross‐coupling of C(sp2)−H and S−H was achieved with liberation of H2. Such a unique transformation opens up a door toward direct C−H and S−H coupling for valuable organosulfur chemistry.
Achieving highly efficient hydrogen (H2) evolution via artificial photosynthesis is a great ambition pursued by scientists in recent decades because H2 has high specific enthalpy of combustion and benign combustion product. [FeFe]-Hydrogenase ([FeFe]-H2ase) mimics have been demonstrated to be promising catalysts for H2 photoproduction. However, the efficient photocatalytic H2 generation system, consisting of PAA-g-Fe2S2, CdSe QDs and H2A, suffered from low stability, probably due to the hole accumulation induced photooxidation of CdSe QDs and the subsequent crash of [FeFe]-H2ase mimics. In this work, we take advantage of supramolecular interaction for the first time to construct the secondary coordination sphere of electron donors (HA−) to CdSe QDs. The generated secondary coordination sphere helps realize much faster hole removal with a ~30-fold increase, thus leading to higher stability and activity for H2 evolution. The unique photocatalytic H2 evolution system features a great increase of turnover number to 83600, which is the highest one obtained so far for photocatalytic H2 production by using [FeFe]-H2ase mimics as catalysts.
Based on 6-hydroxyindole BODIPY with a Schiff-base structure, NIR fluorescence with impressively high selectivity is triggered by deprotonation of the phenol group upon binding with Zn(2+) due to the chelation-enhanced fluorescence effect, thus realizing a promising application in bioimaging of Zn(2+).
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