Cyanide-based Covalent Organic Frameworks for Enhanced Overall Photocatalytic Hydrogen Peroxide Production.

Photocatalytic oxygen reduction to produce hydrogen peroxide (H2O2) is a promising route to providing oxidants for various industrial applications. However, the lack of well-designed photocatalysts for efficient overall H2O2 production in pure water has impeded ongoing research and practical thrusts. Here we present a cyanide-based covalent organic framework (TBTN-COFs) combining 2,4,6-trimethylbenzene-1,3,5-tricarbonitrile (TBTN) and benzotrithiophene-2,5,8-tricarbaldehyde (BTT) building blocks with water-affinity and charge-separation. The ultrafast intramolecular electron transfer (<500 fs) and prolonged excited state lifetime (748 ps) can be realized by TBTN-COF, resulting in a hole accumulated BTT and electron-rich TBTN building block. Under one sun, the 11013 µmol h-1 g-1 yield rate of H2O2 can be achieved without any sacrificial agent, outperforming most previous reports. Furthermore, the DFT calculation and in situ DRIFTS spectrums suggesting a Yeager-type absorption of *O2⋅- intermediate in the cyanide active site, which prohibits the formation of superoxide radical and revealing a favored H2O2 production pathway.

Coupling Electron Transfer and Redox Site in Boranil Covalent Organic Framework Toward Boosting Photocatalytic Water Oxidation.

The efficient polymeric semiconducting photocatalyst for solar-driven sluggish kinetics with multielectron transfer oxygen evolution has spurred scientific interest. However, existing photocatalysts limited by π-conjugations, visible-light harvest, and charge transfer often compromise the O2 production rate. Herein, we introduced an alternative strategy involving a boranil functionalized-based fully π-conjugated ordered donor and acceptor (D-A) covalent organic frameworks (Ni-TAPP-COF-BF2 ) photocatalyst. The co-catalyst-free Ni-TAPP-COF-BF2 exhibits an excellent ~11-fold photocatalytic water oxidation rate, reaching 1404 µmol g-1 h-1 under visible light irradiation compared to pristine Ni-TAPP-COF (123 µmol g-1 h-1 ) alone and surpasses to reported organic frameworks counterpart. Both experimental and theoretical results demonstrate that the push/pull mechanism (metalloporphyrin/BF2 ) is responsible for the appropriate light-harvesting properties and extending π-conjugation through chelating BF2 moieties. This strategy benefits in narrowing band structure, improving photo-induced charge separation, and prolonged charge recombination. Further, the lower spin magnetic moment of M-TAPP-COF-BF2 and the closer d-band center of metal sites toward the Fermi level lead to a lower energy barrier for *O intermediate. Reveal the potential of the functionalization strategy and opens up an alternative approach for engineering future photocatalysts in energy conversion applications.

Ultrathin covalent organic framework nanosheets for enhanced photocatalytic water oxidation.

Photocatalytic water oxidation is a key half-reaction for various solar-to-fuel conversion systems but requires simultaneous water affinity and hole accumulation at the photocatalytic site. Here, we present the rational design and synthesis of an ionic-type covalent organic framework (COF) named tetraphenylporphyrin cobalt and cobalt bipyridine complex (CoTPP-CoBpy3) COF, combining cobalt porphyrin and cobalt bipyridine building blocks as a photocatalyst for water oxidation. The good dispersibility of porous large-size (>2 micrometers) COF nanosheets (≈1.45 nanometers) facilitates local water collection; the ultrafast triplet-state charge transfer (1.8 picoseconds) and prolonged charge separation (1.2 nanoseconds) further contribute to the efficient accumulation of holes in the CoTPP moiety, leading to a photocatalytic dioxygen production rate of 7323 micromoles per gram per hour. Moreover, we have identified an end-on superoxide radical (O2·) intermediate at the active site of the CoTPP moiety and proposed an electron-intermediate cascade mechanism that elucidates the synergistic coupling of electron relay (S1-T1-T1') and intermediate evolution during the photocatalytic process.

Solar utilization beyond photosynthesis.

Natural photosynthesis is an efficient biochemical process which converts solar energy into energy-rich carbohydrates. By understanding the key photoelectrochemical processes and mechanisms that underpin natural photosynthesis, advanced solar utilization technologies have been developed that may be used to provide sustainable energy to help address climate change. The processes of light harvesting, catalysis and energy storage in natural photosynthesis have inspired photovoltaics, photoelectrocatalysis and photo-rechargeable battery technologies. In this Review, we describe how advanced solar utilization technologies have drawn inspiration from natural photosynthesis, to find sustainable solutions to the challenges faced by modern society. We summarize the uses of advanced solar utilization technologies, such as converting solar energy to electrical and chemical energy, electrochemical storage and conversion, and associated thermal tandem technologies. Both the foundational mechanisms and typical materials and devices are reported. Finally, potential future solar utilization technologies are presented that may mimic, and even outperform, natural photosynthesis.

A Photoresponsive Battery Based on a Redox-Coupled Covalent-Organic-Framework Hybrid Photoelectrochemical Cathode.

Photoresponsive batteries promise flexible and low-cost solar-to-electrochemical energy storage (SES), but suffer from a limited SES efficiency due to rapid charge recombination and sluggish redox. Here, we present a porous-shell/core hybrid of covalent organic framework@carbon nanotube. This hybrid ensures long-lived separated charges (τave =3.0 ns) by an electron transfer relay starting from the donor-acceptor molecules to the nanoscale heterojunction. These charges are further allowed to drive high-rate redox of -C=O/-C-O- and -C-N/-C=N+ with facile kinetics. Equipped with this photoelectrochemical cathode, a photoresponsive aqueous battery shows a 5-fold enhancement in SES efficiency (1.1 % at 1 sun) over their counterparts. It is unveiled that the electron relay favors the formation of electron-enriching -C-O- and hole-enriching -C=N+ groups responsible for photoelectrochemical Zn2+ and OTf- storage cascade; and further, the general photo coupled ions transfer (PCIT) process is proposed. This work presents an inspiring photoelectrochemical cathode design and theoretical insight for photoresponsive batteries.

Nanoscale Double-Heterojunctional Electrocatalyst for Hydrogen Evolution.

The active sites and charge/mass transfer properties in electrocatalysts play vital roles in kinetics and thermodynamics of electrocatalysis, and impose direct impacts on electrocatalytic performance, which cannot be achieved by a simplex structure. As a prototype, the authors propose a double-heterojunctional nanostructure of NiS2 /Ni3 C@C containing NiS2 /Ni3 C and Ni3 C/C heterojunctions as a general model to optimize the above issues and boost electrocatalytic performance. During the thermal reorganization, the in situ reaction between NiS2 nanoparticles and carbon induces the formation of Ni3 C between them and constructs tightly contacted two kinds of interfaces among the three components. The TEM and XPS reveal the intimately contacted three components and the as-constructed interacted dual interfaces, further confirming the formation of a porous double-heterojunctional nanostructure. Theoretical calculations uncover that the electron density redistribution occurs at Ni3 C/C interface by spontaneous electron transfer from defected carbon to Ni3 C and lower ΔGH* achieves at NiS2 /Ni3 C interface by the concentrated interfacial charge density, which favors the simultaneous realization of high catalytic activity and rapid charge/mass transfer. When applied for hydrogen evolution reaction (HER), the porous double-heterojunctional NiS2 /Ni3 C@C exhibits excellent HER activity and durability among all pH values. Profoundly, this special double-heterojunctional structure can provide a new model for high-performance electrocatalysts and beyond.

A Pd2+-Free Near-Infrared Fluorescent Probe Based on Allyl Ether Isomerization for Tracking CORM-3 with High Contrast Imaging in Living Systems.

As a CO donor, CORM-3 is widely used nowadays to study the role of CO as a gasotransmitter and potential drug in biological systems. Developing methods to detect CORM-3 in live systems will contribute to these studies. Herein, we developed a novel Pd2+-free near-infrared fluorescent probe CORM3-AE for detecting CORM-3 both in live cells and in vivo. We found that the allyl ether group in CORM3-AE could be cleaved by CORM-3 directly via an isomerization process to release the NIR fluorophore QCy7 and cause distinct NIR fluorescence changes. Importantly, CORM3-AE responds quickly and shows high sensitivity and selectivity for CORM-3 with NIR fluorescence turn-on changes at 743 nm (λex = 662 nm), and when the excitation wavelength is 450 nm, CORM3-AE can respond to CORM-3 with ratiometric fluorescence signals at 743/605 nm. Moreover, CORM3-AE can track CORM-3 in live cells and animals with excellent imaging performance. Thus, this work not only provides a powerful new tool for CORM-3 detection in live systems but also provides a new method to construct CORM-3 probes by allyl ether isomerization.

Asymmetric Oxo-Bridged ZnPb Bimetallic Electrocatalysis Boosting CO2 -to-HCOOH Reduction.

Electrochemical CO2 reduction (ECR) is one of the promising CO2 recycling technologies sustaining the natural carbon cycle and offering more sustainable higher-energy chemicals. Zn- and Pb-based catalysts have improved formate selectivity, but they suffer from relatively low current activities considering the competitive CO selectivity on Zn. Here, lead-doped zinc (Zn(Pb)) electrocatalyst is optimized to efficiently reduce CO2 to formate, while CO evolution selectivity is largely controlled. Selective formate is detected with Faradaic efficiency (FEHCOOH ) of ≈95% at an outstanding partial current density of 47 mA cm-2 in a conventional H-Cell. Zn(Pb) is further investigated in an electrolyte-fed device achieving a superior conversion rate of ≈100 mA cm-2 representing a step closer to practical electrocatalysis. The in situ analysis demonstrates that the Pb incorporation plays a crucial role in CO suppression stem from the generation of the Pb-O-C-O-Zn structure rather than the CO-boosted Pb-O-C-Zn. Density functional theory (DFT) calculations reveal that the alloying effect tunes the adsorption energetics and consequently modifies the electronic structure of the system for an optimized asymmetric oxo-bridged intermediate. The alloying effect between Zn and Pb controls CO selectivity and achieves a superior activity for a selective CO2 -to-formate reduction.

In Vivo Imaging and Tracking Carbon Monoxide-Releasing Molecule-3 with an NIR Fluorescent Probe.

As a water-soluble carbon monoxide-releasing molecule, CORM-3 is widely used as a CO donor to study CO in the life system. CORM-3 can also replace gaseous CO as a therapeutic drug molecule to reveal the physiological and pathological effects of CO in life. Therefore, it is of great importance to visualize and track CORM-3 in the life system. We develop herein a near-infrared (NIR) fluorescent probe CORM3-NIR that can detect CORM-3 both in living cells and in vivo effectively. The probe is based on the unique fluorescent QCy7 and uses a 4-nitrobenzyl group to trap CORM-3, and importantly, it shows good water solubility and responds rapidly, selectively, and sensitively to CORM-3, releasing QCy-7 and producing distinct colorimetric and significant NIR fluorescence change signals at 743 nm. The Stokes shift is up to 81 nm. The probe is also able to detect CORM-3 ratiometrically with fluorescence at 743 and 600 nm. Besides, with low cytotoxicity, the probe also shows good NIR fluorescence bioimaging ability for CORM-3 in live cells and mice, which indicates that CORM3-NIR is an effective probe for tracking and studying CORM-3 in the life system.

NIR fluorescent probe based on a modified rhodol-dye with good water solubility and large Stokes shift for monitoring CO in living systems.

Because of the biological importance of CO, the development of effective probes for the detection of CO in living systems is of great significance. In particular, near-infrared (NIR) fluorescence probes with good water solubility and large Stokes shift are indispensable tools for CO detection in vivo. However, such tools are extremely scarce. Herein, a modified rhodol dye was used to develop a novel NIR fluorescent probe (Rh-NIR-CO) for selective and sensitive detection of CO using the Pd0-mediated Tsuji-Trost reaction. This probe shows good water solubility and rapid CO detecting ability in aqueous buffer at pH 7.4, accompanied by distinct colorimetric and turn-on NIR emission changes at 676 nm with a large Stokes shift (135 nm) and low detection limit (37 nM). Moreover, NIR fluorescence imaging of CO in living cells, zebrafish, and living mice was successfully applied with this probe. These excellent results highlighted Rh-NIR-CO as a promising new tool for in vitro and in vivo detection of CO.

Development of a new ratiometric probe with near-infrared fluorescence and a large Stokes shift for detection of gasotransmitter CO in living cells.

A near-infrared (NIR) ratiometric fluorescent probe, NIR-Ratio-CO, was developed for rapid detection of carbon monoxide (CO) in both solution and living cells through the strategy of Pd0-mediated Tsuji-Trost reaction. This probe shows a rapid, highly specific and sensitive detection process for CO, accompanied by colorimetric and distinct ratiometric fluorescence changes at 655 and 592 nm with a large Stokes shift up to 195 nm. The detection limit for CO was measured to be about 61 nM by the fluorescence method. In addition, this probe was successfully applied for ratiometric imaging of both exogenous and endogenous CO in living cells, indicating that it can be used as a novel tool for ratiometric fluorescent detection of CO in living systems.

Nitrobenzoxadiazole Ether-Based Near-Infrared Fluorescent Probe with Unexpected High Selectivity for H2S Imaging in Living Cells and Mice.

H2S is an important endogenous gasotransmitter, and its detection in living systems is of great significance. Especially, selective and sensitive near-infrared (NIR) fluorescent H2S probes with rapid response and large Stokes shift are highly desirable because of their superiority for in vivo detection. Probes with nitrobenzoxadiazole (NBD) ether as reaction sites have been well-explored recently to detect biothiols or H2S/biothiols simultaneously, rather than to detect H2S selectively. In this work, a new NBD ether-based NIR fluorescent probe was developed, which was unexpectedly found to show high selectivity for H2S over various other analytes including biothiols, making it practical for specific detection of H2S both in vitro and in vivo. Upon response to H2S, this probe showed rapid and significant turn-on NIR emission changes centered at 744 nm within 3 min, together with a remarkable large Stokes shift (166 nm) and high sensitivity (LOD: 26 nM). Moreover, imaging exogenous and endogenous H2S in living cells and rapid imaging of H2S in living mice with this probe was successfully applied with excellent performance.

A near-infrared fluorescent probe for imaging endogenous carbon monoxide in living systems with a large Stokes shift.

Near-infrared (NIR) fluorescent probes with a large Stokes shift are very practical tools for bioimaging applications. Carbon monoxide (CO) is a key gaseous signal molecule and its imaging in living systems has attracted great attention in recent years. In this work, a very easy-to-get NIR fluorescent probe with a remarkable large pseudo-Stokes shift (238 nm) for detection of CO was reported. This probe was found to show a rapid NIR fluorescent turn-on response for CO with high selectivity, high sensitivity and a low detection limit (38 nM). Moreover, imaging CO in living cells and animals with this probe was successfully applied with a high signal-to-noise ratio. The results indicate that this probe can be used as a new practical tool for imaging of endogenous CO in living systems.

Readily prepared iminocoumarin for rapid, colorimetric and ratiometric fluorescent detection of phosgene.

In this paper, a new colorimetric and ratiometric fluorescent probe for the rapid detection of phosgene is reported. This probe is based on a readily prepared and highly fluorescent iminocoumarin, which reacts rapidly with phosgene to form a cyclic carbamate product to produce, distinctive colorimetric and ratiometric fluorescent signal changes. The detection of phosgene with this probe is fast (complete within 2 min), highly selective and sensitive with a detection limit of 27 nM in solution. Moreover, this probe can be used to prepare easy-to-use paper test strips for convenient visual and fluorescent detection of phosgene gas even at a concentration of 0.1 mg/L. Overall, this work provides a very promising dual colorimetric and ratiometric fluorescent probe for rapid and sensitive detection of phosgene both in solution and in the gas phase.

kHz-order linewidth controllable 1550 nm single-frequency fiber laser for coherent optical communication.

A kHz-order linewidth controllable 1550 nm single-frequency fiber laser (SFFL) is demonstrated for the first time to our best knowledge. The control of the linewidth is realized by using a low-pass filtered white Gaussian noise (WGN) signal applied on a fiber stretcher in an optical feedback loop. Utilizing WGN signals with different signal amplitudes An and different cutoff frequencies fc, the linewidths are availably controlled in a wide range from 0.8 to 353 kHz. The obtained optical signal-to-noise ratio (OSNR) is more than 72.0 dB, and the relative intensity noise (RIN) at frequency greater than 40 MHz reaches -148.5 dB/Hz which approaches the shot noise limit (-152.9 dB/Hz). This kHz-order linewidth controllable SFFL is meaningful and valuable, for optimizing the receiver sensitivity and bit error rate (BER) performance of the coherent optical communication system based on high-order quadrature amplitude modulation (QAM).

Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser.

An ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser based on self-injection locking has been demonstrated. By the use of a tunable narrow-band fiber Fabry-Perot interferometer, the laser wavelength could be flexibly tuned from 1527 to 1563 nm with linewidths of < 700 Hz. The laser frequency noise is less than 40 dB re Hz/Hz1/2 at low frequencies (< 100 Hz) and reaches -5 dB re Hz/Hz1/2 at around 25 kHz. The measured relative intensity noise (RIN) is less than -130 dB/Hz with regard to frequencies of over 3 MHz, while the obtained linear polarization extinction ratio (LPER) is higher than 28 dB. This ultra-narrow linewidth low-noise tunable single-frequency linear-polarization fiber laser provides a promising candidate for high-order quadrature amplitude modulation (QAM) optical communication system.

Advanced modulation formats for 400-Gbps short-reach optical inter-connection.

Besides the long-haul optical networks covering over thousands of kilometers for backbone transmission, short reach optical networks (SR-ONs) are widely deployed in metro-area for aggregation and accessing. The SR-ONs include the metro optical transport networks (Metro-OTN), optical access networks or other optical inter-connection systems with even shorter distance. As predicted, the growing bandwidth demanding from SR-ONs will be much more than that from the long-haul optical networks in the near future. Besides, there are tremendous amounts of optical terminals and end-users in SR-ONs compared with the long-haul transmission systems and thus will induce large cost and huge energy consumption. So, the power and cost efficiency should be the key consideration for SR-ONs besides the transmission performance. To improve the power and cost efficiency in SR-ONs, advanced modulations and detection techniques based on low power, low cost and integrated optical modulators should be utilized. In this paper, different advanced modulation formats have been discussed. 56Gbps PAM4, 112Gbps poly-binary and 100Gbps DMT that can be used to realize 400-Gbps SR-ONs for different applications have also been demonstrated respectively. In addition, low-cost and low-power opto-electronic components suitable for SR-ONs, the impairments induced by all kinds of defects and bandwidth limitation of opto-electronic components and the corresponding compensation techniques based on DSP algorithms have also been discussed in the experiments.

Palladium-based nanostructures with highly porous features and perpendicular pore channels as enhanced organic catalysts.

Channeling a good catalyst: Highly porous palladium nanostructures (pPdNs) with perpendicular pore channels were prepared under mild conditions. The combination of high surface area and rich edge/corner atoms gives pPdNs better catalytic performance than known Pd catalysts for the hydrogenation of nitrobenzene and styrene and the Suzuki coupling reaction.

Photonic generation of ultrawideband monocycle and doublet pulses by using a semiconductor-optical-amplifier-based wavelength converter.

Photonic generation of ultrawideband (UWB) monocycle and doublet pulses is experimentally demonstrated using a cascaded electroabsorption modulator (EAM) and semiconductor optical amplifier by exploiting a combination of cross-absorption modulation and cross-gain modulation. The polarities and shapes of UWB monocycle and doublet pulses can be simply controlled using an optical time-delay controller and the reverse voltage applied to the EAM. The corresponding measured rf spectra meet the UWB criteria.

Reduction of patterning effects in SOA-based wavelength converters by combining cross-gain and cross-absorption modulation.

A scheme for mitigating patterning effects in wavelength conversion by using a concatenated semiconductor optical amplifier (SOA) and electroabsorption modulator (EAM) is proposed. The optimization of the parameters of the semiconductor devices and receiver electronics is theoretically investigated. The bit error ratio (BER) of the output signals in both the co-propagating and the counter-propagating configurations is quantitatively evaluated. The simulation results indicate that the patterning effect in wavelength conversion due to the slow recovery of the carrier density in the SOA can be well compensated by a concatenated EAM. The simulation results are confirmed by preliminary pump-probe experiment using a 10Gb/s clock pulse train.