Nature uses organic molecules for light harvesting and photosynthesis but most man-made water splitting catalysts are inorganic semiconductors. Organic photocatalysts, while attractive because of their synthetic tunability, tend to have low quantum efficiencies for water splitting. Here we present a crystalline covalent organic framework (COF) based on a benzobis(benzothiophene sulfone) moiety that shows a much higher activity for photochemical hydrogen evolution than its amorphous or semi-crystalline counterparts. The COF is stable under long-term visible irradiation and shows steady photochemical hydrogen evolution with a sacrificial electron donor for at least fifty hours. We attribute its high quantum efficiency of FS-COF to its crystallinity, its strong visible light absorption, and its wettable, hydrophilic 3.2 nm mesopores. These pores allow the framework to be dye sensitized, leading to a further 61% enhancement in the hydrogen evolution rate up to 16.3 mmol g-1 h-1. The COF also retained its photocatalytic activity when cast as a thin film onto a support. Photocatalytic solar hydrogen production-or water splitting-offers an abundant clean energy source for the future. The use of dispersed, powdered photocatalysts or thin catalyst films is attractively simple, but so far, no catalyst satisfies the combined requirements of cost, stability and solar-to-hydrogen efficiency. Since the first report of TiO2 as a photocatalyst, 1 many inorganic semiconductors have been explored for water splitting, both in photoelectrochemical cells and as photocatalyst suspensions. 2-4 Recently, organic semiconductors have emerged as promising materials for photocatalytic hydrogen and oxygen evolution. 5-7 Poly(p-phenylene) was first reported as a photocatalyst for hydrogen evolution in 1985, 8,9 but its activity was poor and limited to the ultraviolet spectrum. Since then, more active organic materials have been reported as visible light photocatalysts for hydrogen production using sacrificial donors. This started with carbon nitrides 5,10 followed by poly(azomethine)s, 11 conjugated microporous polymers (CMPs), 6,12,13 linear conjugated polymers, 12,14-16 and covalent triazine-based frameworks (CTFs). 17-19 Carbon nitrides were further developed into hybrid systems that facilitate overall water splitting to produce both hydrogen and oxygen, for example by including metal co-catalysts. 20 CMPs were also claimed to exhibit overall photocatalytic water splitting. 21 However, while it is possible to tune semiconductor properties such as band gap by modular copolymerization strategies, 6 organic materials such as carbon nitrides, conjugated polymers and CTFs lack long-range order: they are amorphous or semi-crystalline. 17,22 This lack of order might limit the transport of photoactive charges to the catalyst surface. 23 More generally, it is challenging to construct atomistic structure-property relationships for materials where the three-dimensional architecture is poorly defined. Covalent organic frameworks (COFs) 24-26 are a cla...

The desolvated polyhedral framework material NOTT-112 shows an excess H(2) uptake of 7.07 wt% between 35 and 40 bar at 77 K, and a total H(2) uptake of 10 wt% at 77 bar and 77 K.

The efficient delivery of nanomaterials to specific targets for in vivo biomedical imaging is hindered by rapid sequestration by the reticuloendothelial system (RES) and consequent short circulation times. To overcome these two problems, we have prepared a new stealth PEG polymer conjugate containing a terminal 1,1-bisphosphonate (BP) group for strong and stable binding to the surface of ultrasmall-superparamagnetic oxide nanomaterials (USPIOs). This polymer, PEG(5)-BP, can be used to exchange the hydrophobic surfactants commonly used in the synthesis of USPIOs very efficiently and at room temperature using a simple method in 1 h. The resulting nanoparticles, PEG(5)-BP-USPIOs are stable in water or saline for at least 7 months and display a near-zero ζ-potential at neutral pH. The longitudinal (r1) and transverse (r2) relaxivities were measured at a clinically relevant magnetic field (3 T), revealing a high r1 of 9.5 mM–1 s–1 and low r2/r1 ratio of 2.97, making these USPIOs attractive as T1-weighted MRI contrast agents at high magnetic fields. The strong T1-effect was demonstrated in vivo, revealing that PEG(5)-BP-USPIOs remain in the bloodstream and enhance its signal 6-fold, allowing the visualization of blood vessels and vascular organs with high spatial definition. Furthermore, the optimal relaxivity properties allow us to inject a dose 4 times lower than with other USPIOs. PEG(5)-BP-USPIOs can also be labeled using a radiolabeled-BP for visualization with single photon emission computed tomography (SPECT), and thus affording dual-modality contrast. The SPECT studies confirmed low RES uptake and long blood circulation times (t1/2 = 2.97 h). These results demonstrate the potential of PEG(5)-BP-USPIOs for the development of targeted multimodal imaging agents for molecular imaging.

Three series of conjugated microporous polymers (CMPs) were studied as photocatalysts for hydrogen production from water using a sacrificial hole scavenger. In all cases, dibenzo[b,d]thiophene sulfone polymers outperformed their fluorene analogues. A porous network, S-CMP3, showed the highest hydrogen evolution rates of 6076 μmol h −1 g −1 (λ > 295 nm) and 3106 μmol h −1 g −1 (λ > 420 nm), with an external quantum efficiency of 13.2% at 420 nm. S-CMP3 outperforms its linear structural analogue, P35, whereas in other cases, nonporous linear polymers are superior to equivalent porous networks. This suggests that microporosity might be beneficial for sacrificial photocatalytic hydrogen evolution, if suitable linkers are used that do not limit charge transport and the material can be wetted by water as studied here by water sorption and quasi-elastic neutron scattering.

Neutron powder diffraction experiments on D(2)-loaded NOTT-112 reveal that the axial sites of exposed Cu(II) ions in the smallest cuboctahedral cages are the first, strongest binding sites for D(2) leading to an overall discrimination between the two types of exposed Cu(II) sites at the paddlewheel nodes. Thus, the Cu(II) centers within the cuboctahedral cage are the first sites of D(2) binding with a Cu-D(2) distance of 2.23(1) A.

Two rhodamine-based chemosensors (1 and 2) were designed, and their sensing behavior toward metal ions was investigated by fluorescence spectroscopies. 1 and 2 achieved tuning the selectivity to Fe(III) and Cr(III) in 100% aqueous solution, whereas other ions including Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I) induced basically no spectral change, which constituted a Fe(III)-selective and a Cr(III)-selective fluorescent chemosensor, respectively.

Mimicking natural photosynthesis to convert CO2 with H2O into value-added fuels achieving overall reaction is a promising way to reduce the atmospheric CO2 level. Casting the catalyst of two or more catalytic sites with rapid electron transfer and interaction may be an effective strategy for coupling photocatalytic CO2 reduction and H2O oxidation. Herein, based on the MOF ∪ COF collaboration, we have carefully designed and synthesized a crystalline hetero-metallic cluster catalyst denoted MCOF-Ti6Cu3 with spatial separation and functional cooperation between oxidative and reductive clusters. It utilizes dynamic covalent bonds between clusters to promote photo-induced charge separation and transfer efficiency, to drive both the photocatalytic oxidative and reductive reactions. MCOF-Ti6Cu3 exhibits fine activity in the conversion of CO2 with water into HCOOH (169.8 μmol g−1h−1). Remarkably, experiments and theoretical calculations reveal that photo-excited electrons are transferred from Ti to Cu, indicating that the Cu cluster is the catalytic reduction center.

Porous metal-organic frameworks (MOFs) are the subject of considerable research interest because of their high porosity and capability of specific binding to small molecules, thus underpinning a wide range of materials functions such as gas adsorption, separation, drug delivery, catalysis, and sensing. MOFs, constructed by the designed assembly of metal ions and functional organic linkers, are an emerging class of porous materials with extended porous structures containing periodic binding sites. MOFs thus provide a new platform for the study of the chemistry and reactivity of small molecules in confined pores using advanced diffraction and spectroscopic techniques. In this review, we focus on recent progress in experimental investigations on the crystallographic, dynamic and kinetic aspects of substrate binding within porous MOFs. In particular, we focus on studies on host-guest interactions involving open metal sites or pendant functional groups in the pore as the primary binding sites for guest molecules.