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Both experimental and computational results suggest that readily crossing conical intersections (CIs) for AIE-gens in solutions significantly reduces fluorescence, whereas crossing CIs is restricted in solids.

Energy loss caused by exciton binding energy (

The design of Faradaic battery electrodes with high rate capability and long cycle life comparable to those of supercapacitors is a grand challenge. Here, we bridge this performance gap by taking advantage of a unique ultrafast proton conduction mechanism in vanadium oxide electrode, developing an aqueous battery with untrahigh rate capability up to 1000 C (400 A g −1 ) and extremely long life of 0.2 million cycles. The mechanism is elucidated by comprehensive experimental and theoretical results. Instead of slow individual Zn 2+ transfer or Grotthuss chain transfer of confined H + , the ultrafast kinetics and excellent cyclic stability are enabled by rapid 3D proton transfer in vanadium oxide via the special pair dance switching between Eigen and Zundel configurations with little constraint and low energy barriers. This work provides insight into developing high-power and long-life electrochemical energy storage devices with nonmetal ion transfer through special pair dance topochemistry dictated by hydrogen bond.

Molecular packing patterns are crucial factors determining electron/energy transfer processes that are critical for the optoelectronic properties of organic thin film devices. Herein, the polarization-selective ultraviolet/infrared (UV/IR) mixed frequency ultrafast spectroscopy is applied to investigate the relative molecular orientations in two organic thin films of 7-(diethylamino)coumarin-3-carboxylic acid (DEAC) and perylene. The signal anisotropy changes caused by intermolecular energy/electron transfers are utilized to calculate the cross angles between the electronic transition dipole moment of the donor and the vibrational transition dipole moments of the acceptor, yielding the relative orientation between two adjacent molecules. Using this method, the relative orientation angle in DEAC film is determined to be 53.4°, close to 60° of its single crystalline structure, and that of the perylene film is determined to be 6.2°, also close to −0.2° of its single crystalline structure. Besides experimental uncertainties, the small difference between the angles determined by this method and those of single crystals also results from the fact that the thin film samples are polycrystalline where some of the molecules are amorphous.

Diphenylphosphine (DPP) was incorporated facilely into a typical aggregation-caused quenching (ACQ) luminophore to facilitate ACQ-to-AIE transformation. The rapid intersystem crossing process was explored as the DPP-based AIE mechanism.

The enhancement factor of surface-enhanced Raman scattering (SERS) is usually approximated by the fourth power of local electric field-enhanced strength. However, the applicability of the plane wave approximation used in this method remains a major problem in the theoretical study of SERS and the comparison with experiment results. In this work, we simultaneously calculated the local incident field enhancement factor under plane wave excitation and emission enhancement factor of a dipole in common SERS structures. For isolated particles and dimers, the local field enhancement factors are in good agreement with the emission enhancement factors. Nevertheless, the fourth power approximation method fails to predict the enhancement factors for structures on the substrate. The results show that when the SERS structures locate on the substrate, the local field method under-estimates the enhancement factor. The Purcell effect was used and compared with the emission enhancement. It indicates that the Purcell factor matches the emission enhancement quite well for the particles in homogeneous medium, while the Purcell factor over-estimates the emission enhancement for the particles on the substrate. These results are helpful for the SERS studies and the enhancement factor calculations.

The low photoluminescence (PL) quantum yields of transition metal dichalcogenide monolayers have been a limiting factor for their optoelectronic applications. Various and even inconsistent mechanisms have been proposed to modulate their PL efficiencies. Herein, we use PL/Raman microspectroscopy and the corresponding in situ mapping, atomic force microscopy, and field-effect transistor (FET) characterization to investigate the changes in the structural and optical properties of monolayer MoS2. Relatively low power density (

Conical intersections (CIs) provide effective fast nonradiative decay pathways for electronic excitation, which can significantly influence molecular photoluminescence properties. However, in many cases, crossing a CI does not have direct observables, making studies of CIs experimentally challenging. Herein, the theoretically predicted double CIs by cis–trans twisting and cyclization in tetraphenyl ethylene, a well-known aggregation-induced emission molecule, are investigated with excitation dependent ultrafast UV/IR spectroscopy and fluorescence. Both the fluorescence quantum yield and the efficiency of cyclization are found to be smaller with a shorter excitation wavelength. An abrupt change occurs at about 300–310 nm. The results imply that crossing the twisting CI has a larger barrier than the cyclization CI, and the cis–trans twisting motion is probably involved with large solvation reorganization.

The mechanism of aggregation-induced emission, which overcomes the common aggregation-caused quenching problem in organic optoelectronics, is revealed by monitoring the real time structural evolution and dynamics of electronic excited state with frequency and polarization resolved ultrafast UV/IR spectroscopy and theoretical calculations. The formation of Woodward-Hoffmann cyclic intermediates upon ultraviolet excitation is observed in dilute solutions of tetraphenylethylene and its derivatives but not in their respective solid. The ultrafast cyclization provides an efficient nonradiative relaxation pathway through crossing a conical intersection. Without such a reaction mechanism, the electronic excitation is preserved in the molecular solids and the molecule fluoresces efficiently, aided by the very slow intermolecular charge and energy transfers due to the well separated molecular packing arrangement. The mechanisms can be general for tuning the properties of chromophores in different phases for various important applications.

x-membered lactams were synthesized via either an amidation of sp3 C-H bonds or an electrophilic substitution of arenes via Ir-nitrene intermediates. With the employment of a readily available iridium catalyst in dichloromethane or hexafluoro-2-propanol, a wide range of lactams were synthesized in good to excellent yields with high selectivity.

The Fermi level of graphene on different substrates usually changes significantly due to the interface difference between graphene and two-dimensional semiconductors. This feature opens many possibilities of manipulating optoelectronic devices by constructing graphene heterostructures through interface modification. Herein, we report the fabrication and optoelectronic response of an unconventional heterojunction device based on a graphene-MoSe

The aggregation morphologies of conjugated polymers in solutions and solid films are important for their optoelectronic applications. Due to the amorphous state of the polymers, it remains a great challenge to determine their conformations in either liquids or solids. Herein, a ps/fs synchronized 2D IR technique is applied to investigate the molecular conformations of a high-mobility n-type low-bandgap copolymer, N2200, dissolved in CHCl3 and CCl4, and in solid films cast from both solutions by the vibrational cross-angle method. In CCl4, the polymer forms more aggregates and folds more and the backbone dihedral angle of C–C(NDI)/C–S(Thiophene) of its average conformation is about 10° more distorted than that in CHCl3 and the most stable conformation for a free molecule. Anti-intuitively, the solid films cast from both solutions have the same molecular conformation, and the conformation is similar to that of the polar CHCl3 rather than the conformation of the less polar CCl4. The results imply that the interaction between the polymer backbones is probably stronger than its interaction with CCl4, which can naturally guide the rearrangement of polymer chains during the evaporation of solvent molecules. This work also implies that the balance and competition between the polymer/polymer interaction and the polymer/solvent interaction seem to be the dominant factors responsible for what morphology can form in a solid film cast from solution. It is not always true that different molecular conformations must exist in solid films grown from different solutions with different polarity or different extents of aggregates with different conformations.

The low photoluminescence (PL) quantum yields of transition metal dichalcogenide monolayers have been a limiting factor for their optoelectronic applications. Various and even inconsistent mechanisms have been proposed to modulate their PL efficiencies. Herein, we use PL/Raman microspectroscopy and the corresponding

A disordered phase in Li‐deposit nanostructure is greatly attractive, but plagued by the uncontrollable and unstable growth, and the nanoscale characterization in the structure. Here, fully characterized in cryogenic transmission electron microscopy (cryo‐TEM), more robust amorphous‐Li (ALi) clusters are revealed and effectively regulated on heteroatom‐activating electronegative sites and an advanced solid electrolyte interphase (SEI) layer. Heteroatom‐activating electronegative sites capably enhance the electrostatic interaction of Li+ and heteroatom‐doping graphene‐like film (HDGs), meaning lower Li diffusion barrier and larger binding energy that is confirmed by small nucleation overpotentials of 13.9 and 10 mV at 0.1 mA cm−2 in the fluoroethylene carbonate‐adding ester‐based (FEC‐ester) and LiNO3‐adding ether‐based (LiNO3‐ether) electrolytes. Orderly multilayer SEI structure comprised of inorganic‐rich components enables fast ion transports and durable capabilities to construct highly reversible and long‐term plating/stripping cycling. ALi cluster anodes exhibit non‐crystalline morphologies and perform ultrastable dendrite‐free cycling over 2800 times. Stable ALi clusters are also grown in LiFePO4 (LFP) (LFP‐ALi‐HDGs‐N||LiFePO4 [LFP]) full cells with advantageous capacities up to 165.5 and 164.3 mAh g−1 in these optimized electrolytes at 0.1 C; the remarkable capacity retentions maintain to 93% and 91% after 150 cycles at 0.2 C. Structure viability, electrochemical reversibility, and excellent performance in ALi clusters are effectively regulated., Structure viability, electrochemical reversibility, and excellent performance in amorphous Li (ALi) clusters are effectively regulated on the heteroatom‐activating electronegative sites and advanced, multilayer‐ordered, and robust solid electrolyte interphase systems for a more robust ALi cluster anode that exhibits non‐crystalline morphologies and performs ultrastable dendrite‐free cycling over 2800 cycles. Stable ALi clusters are also grown in LFP‐ALi‐HDGs‐N||LiFePO4 (LFP) full cells with advantageous capacities.

Aggregation-induced emission (AIE), usually referring to the phenomenon in which molecules emit more strongly in the aggregate state than in the solution state, is intriguing and promising in various optoelectronic and biosensing applications. In this Perspective, the basic principles that can lead to AIE and experimental evidence to reveal the AIE mechanism of tetraphenyl ethylene (TPE)-type molecules are discussed. AIE is the consequence of two factors: (1) the fast energy dissipation by crossing a conical intersection (CI) in solutions but not in solids results in low luminescence efficiencies in the solutions, and (2) the weak intermolecular coupling and thus slow intermolecular energy/charge transfers in the AIE solids effectively prevent quenching and result in relatively high luminescence efficiencies. The key to AIE is that the luminescence efficiency is tuned by controlling molecules to cross or not to cross a CI by changing the phase of molecules. How fast a molecule can cross a CI is dependent on the energy barrier of isomerization, which can be tuned in many ways, including mechanical or electrical stimuli, in addition to changing phases. Barrier-dependent crossing CI also results in a very important consequence: excitation-wavelength-dependent fluorescence yield within one electronic excited state, an anti-Vavilov's rule phenomenon. In principle, there can be an alternative way to tune luminescence efficiency by manipulating the formation of CIs instead of crossing or not crossing them. This approach relies on the fact that the electronic ground state and the excited state have many different properties, e.g., dipole moment. By tuning the environment, e.g., dielectric constant, to favor or disfavor one state, one may be able to lift or lower the potential surface of one state so that the potential surfaces of two states can vary between intersected and not contacted.

Lithium metal is a promising anode utilized in cutting-edge high-energy batteries owing to the low density, low electrochemical potential, and super high theoretical capacity. Unfortunately, continuous uncontrollable lithium dendrite growth and ‘dead’ lithium result in capacity decay, low coulombic efficiency and short circuit, severely hindering the practical utilization of lithium anode. Herein, we propose a three-dimensional porous lithiophilic current collector for lithium storage. The conductive 3D structure constructed by carbon fiber (CF) can well accommodate the deposited lithium, eliminating volume change between the lithium depositing/stripping process. Moreover, the polydopamine (PDA) coating on the CF surface possesses a large number of polar groups, which can homogenize Li+ ions distribution and apply as the sites for lithium deposition, decreasing nucleation overpotential. As a result, under the 1 mA cm−2 current density, the PDA coated CF (PDA@CF) electrode exhibits high CE (∼98%) for 1000 cycles. Galvanostatic measurements demonstrate that the Li anode using PDA@CF achieves 1000 h cycling life under 1 mA cm−2 with a low overpotential (

Organic materials with long-lived, color-tunable phosphorescence are potentially useful for optical recording, anti-counterfeiting, and bioimaging. Herein, we develop a series of novel host-guest organic phosphors allowing dynamic color tuning from the cyan (502 nm) to orange red (608 nm). Guest materials are employed to tune the phosphorescent color, while the host materials interact with the guest to activate the phosphorescence emission. These organic phosphors have an ultra-long lifetime of 0.7 s and a maximum phosphorescence efficiency of 18.2 %. Although color-tunable inks have already been developed using visible dyes, solution-processed security inks that are temperature dependent and display time-resolved printed images are unprecedented. This strategy can provide a crucial step towards the next-generation of security technologies for information handling.

Methods and materials, Mathematical formula expressions of calculation principle, Influence of density of single crystals and shape of light sources, Optical images of MoS2 film at different magnifications, Size mapping of a MoS2 film, PL mapping

The molecular structure of a catalytically active key intermediate is determined in solution by employing 2D IR spectroscopy measuring vibrational cross-angles. The formate intermediate (2) in the formic acid dehydrogenation reaction catalyzed by a phosphorus–nitrogen PN(3)P–Ru catalyst is elucidated. Our spectroscopic studies show that the complex features a formate ion directly attached to the Ru center as a ligand, and a proton added to the imine arm of the dearomatized PN(3)P* ligand. During the catalytic process, the imine arms are not only reversibly protonated and deprotonated, but also interacting with the protic substrate molecules, effectively serving as the local proton buffer to offer remarkable stability with a turnover number (TON) over one million.

Low cost, safety, and environmental benignity make rechargeable aqueous Zn/MnO2 batteries promising candidates for large-scale energy storage. However, the synthesis of MnO2 with excellent electrochemical performance is limited to the traditional hydrothermal method, which is difficult to scale up for mass production. Herein, a ball-milling approach is developed to rapidly obtain Mn3O4 nanoparticles in large quantity. As the cathode material of aqueous zinc ion battery, Mn3O4 gradually transforms to e-MnO2 in 1 M ZnSO4 + 1 M MnSO4 aqueous electrolyte with increasing cycles. Benefiting from the unexpected phase transition from Mn3O4 to e-MnO2, the cathode delivers a specific capacity of 221 mAh g–1 at a current density of 100 mA g–1 and a good long-term cyclic stability over 500 cycles with 92% capacity retention at a high rate of 500 mA g–1. The excellent battery performance combined with the cost-effective preparation procedure, the good safety of aqueous mild electrolyte, and the easy cell assembly are ...

In contrast to the conventional strategy of modifying the reactivities and selectivities of the transition metal and organocatalysts by varying the steric and electronic properties of organic substituent groups, we hereby demonstrate a novel approach that the sigma (σ) nucleophilicity of the imine arm can be significantly enhanced in a pseudodearomatized PN3P* pincer ligand platform to reach unprecedented N-heterocyclic carbene-like reactivity. Accordingly, the imine arm of the PN3P*Ni-H pincer complex efficiently catalyzes the hydrosilylation of aldehydes, cycloaddition of carbon dioxide (CO2) to epoxides, and serves as a ligand in the Ru-catalyzed dehydrogenative acylation of amines with alcohols.

Most Li-metal batteries can work safely only under 45 °C and have risks of burning or explosion. A novel nonflammable Li-battery is developed to address the challenge, using an interpenetrating rigid-flexible poly (aryl-ether-ketone) nonwovens (PAEKNW) cross-linked with poly(ethylene glycol) dimethacrylate electrolyte to transport lithium ions. The hybridized polymer electrolyte possesses a high ionic conductivity of 1.2 × 10−3 S cm−1 at room temperature and a wide electrochemical window with decomposition voltage higher than 4.5V. It does not readily catch fire or shrink, even under open flame, and shows no noticeable volumetric expansion or contraction at 80 °C, in stark contrast to most liquid-electrolytes-based or gel batteries. Even after cut off by one-third, the battery continues to function. The unique bi-functional molecular design of the polymer electrolyte, which guarantees simultaneously a very rare combination of thermal and mechanical stability, high ion conductivity, and a wide electrochemical window at room temperature, is the key factor responsible for the excellent comprehensive performances.

This article investigates structures of ionic liquids., This article investigates structures of ionic liquids. Using a high-powered multiple-mode two dimensional infrared spectroscopic technique, we measure the anisotropy of interionic vibrational coupling in ionic liquids. Such anisotropy reports the relative orientation between cations and anions. Surprisingly, opposite to the well-propagated idea of ion pairing, a random orientation between the nearest non-spherically symmetric cation and anion is observed in ionic liquids. On the one hand, numerous previous experiments and theoretical calculations have shown that ionic liquids are highly ordered at the mesoscale, forming a bicontinuous nanostructure of ionic domains and hydrophobic domains. On the other hand, our results clearly prove that the ion ordering within the ionic domains is essentially random. Such an ordering at the larger scale (nanometers) and a lack of ordering at the smaller scale (sub-nanometer) is very rare for most liquids, or may even be unique to ionic liquids. Herein, we propose that ionic liquids may be regarded as 3D interconnecting nanocomposites of molten-salt-like domains and molecular-liquid-like domains. Such unique structuring could explain the fact that ionic liquids, like composite materials, often possess favorable properties of both “ionic” and “molecular” components.

A dearomatized PN3P*–nickel hydride complex has been prepared using an oxidative addition process. The first nickel-catalyzed hydrosilylation of CO2 to methanol has been achieved, with unprecedented turnover numbers. Selective methylation and formylation of amines with CO2 were demonstrated by such a PN3P*–nickel hydride complex, highlighting its versatile functions in CO2 reduction.

A Mg2+/Na+ hybrid aqueous battery with high energy density and low cost is constructed using commercial Mn3O4 as a cathode and NaTi2(PO4)3 as an anode for the first time. During electrochemical cycling, spinel Mn3O4 experiences a transition to layered MnO2 hosting Mg2+/Na+ with a high specific capacity and a long cycling life in Mg2+/Na+ hybrid electrolytes. The battery delivers a discharge potential above 1.2 V and an energy density over 47 W h kg−1 (based on the total mass of electrode materials) at a power density of 48 W kg−1; even at a high power density of 400 W kg−1, it delivers an energy density of 23.6 W h kg−1. What is more, the battery shows an excellent cycling performance with 94% capacity retention after 6000 cycles at 10C. The performances drop only very slightly for batteries prepared by an economic and scalable method. The excellent electrochemical properties, combined with the low cost of raw materials and the ease of scaling up which many aqueous batteries lack, make this approach a very promising cost-effective environment-friendly solution for large-scale energy storage.

We report a ruthenium complex containing an N,N′-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. A turnover frequency of 12 000 h–1 and a turnover number of 350 000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO. Mechanistic studies by NMR and DFT calculations indicate that there may be two competitive pathways for the key hydride transfer rate-determining step in the catalytic process.

Hierarchically porous zinc vanadium oxide cathodes contribute to high-rate and ultralong-life aqueous rechargeable zinc batteries., Rechargeable aqueous zinc-ion batteries are promising candidates for large-scale energy storage but are plagued by the lack of cathode materials with both excellent rate capability and adequate cycle life span. We overcome this barrier by designing a novel hierarchically porous structure of Zn-vanadium oxide material. This Zn0.3V2O5·1.5H2O cathode delivers a high specific capacity of 426 mA·h g−1 at 0.2 A g−1 and exhibits an unprecedented superlong-term cyclic stability with a capacity retention of 96% over 20,000 cycles at 10 A g−1. Its electrochemical mechanism is elucidated. The lattice contraction induced by zinc intercalation and the expansion caused by hydronium intercalation cancel each other and allow the lattice to remain constant during charge/discharge, favoring cyclic stability. The hierarchically porous structure provides abundant contact with electrolyte, shortens ion diffusion path, and provides cushion for relieving strain generated during electrochemical processes, facilitating both fast kinetics and long-term stability.

Three model systems are designed to investigate energy transport between molecules on metal nanoparticle surfaces. Energy is rapidly transferred from one carbon monoxide (CO) molecule to another CO molecule or an organic molecule on adjacent surface sites of 2 nm Pt particles within a few picoseconds. On the contrary, energy flow from a surface organic molecule to an adjacent CO molecule is significantly slower and, in fact, within experimental sensitivity and uncertainty the transfer is not observed. The energy transport on particle surfaces (about 2 km s-1) is almost ten times faster than inside a molecule (200 m s-1). The seemingly perplexing observations can be well explained by the combination of electron/vibration and vibration/vibration coupling mechanisms, which mediate molecular energy dynamics on metal nanoparticle surfaces: the strong electron/vibration coupling rapidly converts CO vibrational energy into heat that can be immediately sensed by nearby molecules; but the vibration/vibration coupling dissipates the vibrational excitation in the organic molecule as low-frequency intramolecular vibrations that may or may not couple to surface electronic motions.

Background and Objective Periodically rotated overlapping parallel lines with enhanced reconstruction-echo planar imaging (PROPELLER-EPI) is a promising technique for non-sedated functional imaging due to its unique advantage of motion correction. However, its multiple-blades sampling blood-oxygen-level dependent (BOLD) signal leads to low sampling rate and aliasing of higher frequency physiological signal components such as the cardiac pulsation. Methods In this study, we use near infrared spectroscopy (NIRS) synchronized with pulse sequences of PROPELLER-EPI, utilizing the fact that the optical sensing speed is inherently high. NIRS measures changes of oxyhemoglobin and deoxyhemoglobin to identify the transient states of on-BOLD and off-BOLD, and then labels each blade by temporal co-registration. The labeled blades from multiple epochs of a functional experiment are then used for the k-space data combination and subsequent image reconstruction. An eigenfunction model is proposed for temporal co-registration and to quantify the temporal resolution of the hemodynamic response. Result The experiment of NIRS labeled PROPELLER-EPI was carried out with the optical sampling rate of 10 Hz and the magnetic pulses repetition time of 1000 ms, and the temporal resolution is 20 times better than that of the state-of-the-art sliding-window PROPELLER-EPI. We compared the functional imaging results against the conventional magnetic resonance echo planar imaging-measured activity and achieved an accuracy of 0.9. Conclusions Using the synchronization of NIRS, the proposed imaging scheme provides an effective way to implement PROPELLER-EPI, which features motion free, high SNR, and enhanced spatial-temporal resolution.

Single-atomic-layered materials are important for future electronics. They allow optoelectronic devices to be fabricated at the single-atomic layer level. A single-atomic-layered two-dimensional (2D) transition metal dichalcogenide (TMD) film is usually composed of randomly orientated single-crystalline domains, and the size distribution of the domains on a large-area film has a significant impact on the applications of the film, but the impact is difficult to characterize. We report an approach to evaluate the size of the single-crystalline domains by measuring the second-harmonic generation divergence caused by the domains of different orientations. Using this method, domain size mapping on an 8 × 8 m m 2 region of a continuous M o S 2 film is achieved. This method provides a fast and efficient way of domain size characterization across a large area in a non-destructive and transfer-free manner for single-atomic-layered TMD films.

Knowledge of vibrational energy transfer on a metal nanoparticle/liquid interface is essential for understanding the energy conversion process involved in many heterogeneous nanocatalyses. In this study, we investigate mode-specific vibrational energy transfer between CO molecules on different adsorbate sites on a 1 nm platinum metal nanoparticle/liquid interface by using ultrafast two-dimensional IR spectroscopy. The vibrational energy transport is found to be induced by vibration/vibration coupling with very little surface electron/vibration mediation. The energy transfer rate is determined to be about 1/140 ps–1 from the atop site CO to the bridge site CO, and the specific rate is around 1/400 ps–1 between the two nearest adsorbates. The energy transfer between different adsorbate sites can be described by the dephasing mechanism reasonably well. The mechanical coupling may contribute to the transfer, but analyses suggest that the role of dipole/dipole interaction is a more important factor for the ene...