Effect of Bridging Manner on the Transport Behaviors of Dimethyldihydropyrene/Cyclophanediene Molecular Devices.

A molecule-electrode interface with different coupling strengths is one of the greatest challenges in fabricating reliable molecular switches. In this paper, the effects of bridging manner on the transport behaviors of a dimethyldihydropyrene/cyclophanediene (DHP/CPD) molecule connected to two graphene nanoribbon (GNR) electrodes have been investigated by using the non-equilibrium Green's function combined with density functional theory. The results show that both current values and ON/OFF ratios can be modulated to more than three orders of magnitude by changing bridging manner. Bias-dependent transmission spectra and molecule-projected self-consistent Hamiltonians are used to illustrate the conductance and switching feature. Furthermore, we demonstrate that the bridging manner modulates the electron transport by changing the energy level alignment between the molecule and the GNR electrodes. This work highlights the ability to achieve distinct conductance and switching performance in single-molecular junctions by varying bridging manners between DHP/CPD molecules and GNR electrodes, thus offering practical insights for designing molecular switches.

Core-Hole Excitation Spectra of the Oxides and Hydrates of Fullerene C60 and Azafullerene C59N.

The interaction of fullerenes and their derivatives with environmental molecules such as oxygen or water was crucial for the rational design of low-dimensional materials and devices. In this paper, the near-edge X-ray absorption fine structure (NEXAFS), X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) shake-up satellites were employed to distinguish the oxides and hydrates of the fullerene C60 and azafullerene C59N families. The study includes various isomers, such as the open [5,6] and closed [6,6] isomers of C60O, C60H(OH), C60-O-C60, C60H-O-C60H, C59N(OH) and C59N-O-C59N, based on density functional theory. These soft X-ray spectra offered comprehensive insights into the molecular orbitals of these azafullerene molecular groups. The oxygen K-edge NEXAFS, carbon and oxygen K-edge XPS shake-up satellite spectra provided valuable tools for distinguishing oxides or hydrates of fullerene C60 and azafullerene C59N. Our findings could significantly benefit the development of fullerene functional molecular materials and expand the application scope of soft X-ray spectroscopy as a molecular fingerprinting tool for the fullerene family.

The Optimization of Hole Injection Layer in Organic Light-Emitting Diodes.

Organic light-emitting diodes (OLEDs) are widely recognized as the forefront technology for displays and lighting technology. Now, the global OLED market is nearly mature, driven by the rising demand for superior displays in smartphones. In recent years, numerous strategies have been introduced and demonstrated to optimize the hole injection layer to further enhance the efficiency of OLEDs. In this paper, different methods of optimizing the hole injection layer were elucidated, including using a suitable hole injection material to minimize the hole injection barrier and match the energy level with the emission layer, exploring new preparation methods to optimize the structure of hole injection layer, and so on. Meanwhile, this article can help people to understand the current research progress and the challenges still faced in relation to the hole injection layer in OLEDs, providing future research directions to enhance the properties of OLEDs.

Flexible Transparent Electrode Based on Ag Nanowires: Ag Nanoparticles Co-Doped System for Organic Light-Emitting Diodes.

Flexible organic light-emitting diodes (FOLEDs) have promising potential for future wearable applications because of their exceptional mechanical flexibility. Silver nanowire (Ag NW) networks are the most promising candidates to replace indium tin oxide (ITO), which is limited by its poor bendability. In this study, three different methods including methanol impregnation, argon plasma treatment, and ultraviolet radiation were used to reduce the junction resistance of Ag NWs to optimize the flexible transparent electrodes (FTEs); which were prepared using Ag NWs and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS). Then, the optoelectronic properties of the FTEs were further improved by using a co-doped system of silver nanowires and silver nanoparticles (Ag NPs), the structure of which consisted of PET/Ag NWs: Ag NPs/PEDOT: PSS/DMSO. The largest FOM value of 1.42 × 10-2 ohm-1 and a low sheet resistance value of 13.86 ohm/sq were obtained using the optimized FTEs. The prepared FOLED based on the optimized FTEs had a luminous efficiency of 6.04 cd/A and a maximum EQE of 1.92%, and exhibited no observed decline in efficiency when reaching maximum luminance. After 500 bending tests, the luminance still reached 82% of the original value. It is demonstrated that the FTEs prepared via the co-doped system have excellent optoelectronic properties as well as high mechanical stability.

Radiology Residents' Perceptions of Artificial Intelligence: Nationwide Cross-Sectional Survey Study.

BACKGROUND: Artificial intelligence (AI) is transforming various fields, with health care, especially diagnostic specialties such as radiology, being a key but controversial battleground. However, there is limited research systematically examining the response of "human intelligence" to AI. OBJECTIVE: This study aims to comprehend radiologists' perceptions regarding AI, including their views on its potential to replace them, its usefulness, and their willingness to accept it. We examine the influence of various factors, encompassing demographic characteristics, working status, psychosocial aspects, personal experience, and contextual factors. METHODS: Between December 1, 2020, and April 30, 2021, a cross-sectional survey was completed by 3666 radiology residents in China. We used multivariable logistic regression models to examine factors and associations, reporting odds ratios (ORs) and 95% CIs. RESULTS: In summary, radiology residents generally hold a positive attitude toward AI, with 29.90% (1096/3666) agreeing that AI may reduce the demand for radiologists, 72.80% (2669/3666) believing AI improves disease diagnosis, and 78.18% (2866/3666) feeling that radiologists should embrace AI. Several associated factors, including age, gender, education, region, eye strain, working hours, time spent on medical images, resilience, burnout, AI experience, and perceptions of residency support and stress, significantly influence AI attitudes. For instance, burnout symptoms were associated with greater concerns about AI replacement (OR 1.89; P<.001), less favorable views on AI usefulness (OR 0.77; P=.005), and reduced willingness to use AI (OR 0.71; P<.001). Moreover, after adjusting for all other factors, perceived AI replacement (OR 0.81; P<.001) and AI usefulness (OR 5.97; P<.001) were shown to significantly impact the intention to use AI. CONCLUSIONS: This study profiles radiology residents who are accepting of AI. Our comprehensive findings provide insights for a multidimensional approach to help physicians adapt to AI. Targeted policies, such as digital health care initiatives and medical education, can be developed accordingly.

Leveraging Interlayer Interaction in M-N-C Catalysts for Enhanced Activity in Oxygen Reduction Reactions.

Atomically dispersed metal-nitrogen-carbon (M-N-C) materials are deemed promising catalysts for the oxygen reduction reaction (ORR) in fuel cells. Yet the multilayer nature of M-N-C has been largely neglected in computational analysis. To bridge the gap, we conducted a first-principles investigation using bilayer M-N-C models (TMNx/G-TMNy/G, TM = Mn, Fe, Co, Ni, Cu, G = graphene, x, y = 3 or 4), where the TMs on the top serves as the active center. While in-plane TMN4 at the bottom has a minimal impact on the ORR, out-of-plane TMN3 substantially influences the adsorption free energy of OH through a strong interlayer bonding interaction. By leveraging interlayer interactions, we appreciably lowered the overpotential of selected TMN4 (TM = Co, Ni, Cu) and achieved a minimum of 0.40 V on CoN4/G-CuN3/G. Constant potential calculations revealed weak dependence of OH binding energy on external voltage and obtained results comparable to constant charge calculation. This study provided new physical insight into modulating naturally occurring multilayer M-N-C catalysts.

Rational Design of Photocontrolled Rectifier Switches in Single-Molecule Junctions Based on Diarylethene.

The construction of multifunctional, single-molecule nanocircuits to achieve the miniaturization of active electronic devices is a challenging goal in molecular electronics. In this paper, we present an effective strategy for enhancing the multifunctionality and switching performance of diarylethene-based molecular devices, which exhibit photoswitchable rectification properties. Through a molecular engineering design, we systematically investigate a series of electron donor/acceptor-substituted diarylethene molecules to modulate the electronic properties and investigate the transport behaviors of the molecular junctions using the non-equilibrium Green's function combined with the density functional theory. Our results demonstrate that the asymmetric configuration, substituted by both the donor and acceptor on the diarylethene molecule, exhibits the highest switching ratio and rectification ratio. Importantly, this rectification function can be switched on/off through the photoisomerization of the diarylethene unit. These modulations in the transport properties of these molecular junctions with different substituents were obtained with molecule-projected self-consistent Hamiltonian and bias-dependent transmission spectra. Furthermore, the current-voltage characteristics of these molecular junctions can be explained by the molecular energy level structure, showing the significance of energy level regulation. These findings have practical implications for constructing high-performance, multifunctional molecular-integrated circuits.

Realization of firefly bioluminescence cycle in vitro and in cells.

The quantum yield (Q) of the "cold light" of firefly bioluminescence (BL) is remarkably high due to its nonradiative decay is extremely minimized. Thus, an artificial firefly represents the new generation of biomimetic "cold light" source with highest energy utilization. However, to manufacture a firefly-biomimetic "cold light" in vitro, one has to overcome several challenges including realization of the firefly BL cycle by incorporating the two important enzymes (i.e., firefly luciferase (Fluc) and luciferin-regenerating enzyme (LRE)) in one system. Here in this work, using self-prepared Fluc, LRE, and the main substrates, we realized the firefly BL cycle both in vitro and in cells. Moreover, using combinational analyses of HPLC and nESI-CID-MS/MS, we identified the main chemicals in the metabolic pathways underlying the firefly BL cycle. Using theoretical simulations, we revealed an optimum chemical route which balances the reaction cycle to achieve the highest BL intensity with the least chemical supplies. We anticipate that this pioneering study of the firefly cycle would provide industry with the opportunity to design tunable, economical, biomimetic "cold light" device in near future.

Modulating Charge Separation and Intersystem Crossing in Donor-Switch-Acceptor Systems: A Computational Study.

Charge separation and intersystem crossing play critical roles in various applications of organic long persistent luminescence materials, including light-emitting diodes, chemical sensors, theranostics, and many biomedical and information applications. Using first-principles calculations, we demonstrate that an azobenzene acting as a photoswitch can be used for altering the configuration of a donor-switch-acceptor (D-S-A) molecular system to ensure charge separation and promote intersystem crossing upon photoexcitation. The trans to cis photoisomerization of an azobenzene switch creates an electron trap that stabilizes the charge-separated state. The cis conformation further facilitates the singlet to triplet intersystem crossing in the excited state. Our theoretical study of the D-S-A system may help the design of long persistent luminescent organic devices.

Photoswitchable de/adsorption of an azobenzene-derived surfactant on a silica surface.

The control of surfactant adsorption/desorption, a fundamental process in colloid and surface chemistry, is of crucial importance for surfactant recycling and pollution-free waste treatment. Using first-principles simulations, we designed a photoswitchable approach to realize separation of a photoresponsive surfactant from the adsorbate. We chose a 4-butyl-(4'-(3-trimethylammoniumpropoxy)phenyl)azobenzene cation and quartz as the model system of a surfactant and adsorbate, respectively. Through first-principles calculations, we found that the trans isomer of the surfactant tends to assemble on the silica surface, while the cis isomer tends to be detached from the surface and is instead surrounded by water molecules. The chemical origin of the difference arises from the interactions between the surfactant and solvent, which depend on the molecular conformational change and associated redistribution of charges before and after the isomerization. Intriguingly, the interaction energy between the silica surface and the surfactant does not change significantly with the conformational change of the molecule. Meanwhile, an appreciable void space of the cis conformer attributed to the steric hindrance disfavors the assembling of surfactants on the silica surface, and its significant polarity favors the water environment, which prompts its desorption from the surface. The prediction from computations was then validated by experimental results. We expect our proof-of-concept study on the phototriggered separation of azobenzene-derived surfactant from a silica surface to provide an alternative way of achieving stimuli-responsive separation of surfactant from adsorbates.

A computational study on the tunability of woven covalent organic frameworks for photocatalysis.

A newly reported woven covalent organic framework (COF-505) with a stable and flexible structure is believed to be a promising candidate for photocatalysis. Here, we carried out density functional theory calculations to investigate the properties of COF-505 related to photocatalysis. We first investigated the ability of visible light absorption by this COF-505. Variations of central metal ions and the dihedral angle between two adjacent ligand groups were respectively taken into account for adjusting its light harvesting capabilities. Replacing the original Cu(i) ions with Pd(ii) ions causes a red shift in the visible light region. Increasing the dihedral angle results in an increase of the band gap for COF-505 with Cu(i) and a decrease for COF-505 with Pd(ii), respectively. The potential of COF-505 as a photocatalyst was furthermore explored by studying the adsorption of H2, CO2 and H2O on it. All molecules can be stably adsorbed. In particular, COF-505 with Pd(ii) exhibits appreciable O-H activation of the adsorbed H2O in the presence of a positive charge, which is promising for initiating water splitting. Overall, our results suggest that COF-505 holds great potential for photocatalytic applications.

Energy Materials Design for Steering Charge Kinetics.

Charge kinetics is a critical factor that determines working efficiencies of energy materials in their various applications. It is governed by electronic structures of the materials of interest and can be fine-tuned via purposeful adjustment of electronic structures. Recent advances in the development of energy materials with desirable electronic structures to steering charge kinetics toward specific applications are highlighted here. Two key strategies are presented: one is through the tuning of energy states and the other is to control spatial distributions of charges. Each strategy is described by several different schemes. Finally, the challenges and perspectives in designing energy materials with fine control of charge kinetics are discussed.

Self-Adaptive Switch Enabling Complete Charge Separation in Molecular-Based Optoelectronic Conversion.

Achieving high charge recombination probability has been the major challenge for the practical utilization of molecule-based solar harvesting. Molecular switches were introduced to stabilize the charge separation state in donor-acceptor systems, but it is difficult to seamlessly incorporate the ON/OFF switching actions into the optoelectronic conversion cycle. Here we present a self-adaptive system in which the donor and acceptor are bridged by a switchable moiety that enables a complete charge separation repeatedly. Calculations are presented for a platinum(II) terpyridyl complex with an azobenzene bridge. The charge transfer induced by light extracts electrons from the azobenzene group, automatically triggering a trans → cis isomerization. The resulting conformation suppresses charge recombination. Energized charges are trapped in the acceptor, ready for charge collection by electrodes. The bridge then goes through inverse isomerization to restore the conjugation and conductance. This self-adaptive design provides a novel way to improve the performance of optoelectronic conversion and realize practical solar-harvesting applications in organic molecular systems.

Structure-dependent luminescence of tetra-(4-pyridylphenyl)ethylene: a first-principles study.

Luminescent materials with tunable wavelengths have been attracting much attention due to their many promising applications. In the present work, the recently reported supramolecular coordination complexes of tetra-(4-pyridylphenyl)ethylene (TPPE) that produce variable-wavelength light emissions were investigated by time-dependent density functional theory (TDDFT) calculations. We discovered that variations in the luminescent wavelength of TPPE mainly depend on the structural deviations from molecular planarity, which affect the molecular orbital wavefunction distribution. An interesting trigonometric-functional relationship between the emission wavelength (the emission energy) and the dihedral angle defining deviations from molecular planarity was uncovered. The solvent effect was also considered to reveal the mechanism of the solvent-dependent fluorescence color. These findings may be helpful to rational molecular design for high-performance luminescent materials with tunable color.

Macroscopic Wires from Fluorophore-Quencher Dyads with Long-Lived Blue Emission.

We report the formation of macroscopic wires up to centimeters in length from a series of structurally flexible, covalently tethered small-molecular fluorophore-quencher dyads (FQDs, average MW = 425 Da), comprised of carbazole, melatonin, and cyanobenzoate moieties. These FQDs are nonemissive in organic solutions but become moderately to highly luminescent (ΦF = 0.037-0.39) upon formation of wires with emission maxima in the blue region (446-483 nm). The blue photoluminescence (PL) is ascribed to a combination of singlet charge transfer, localized triplet state, and possibly delayed fluorescence emissions with intrinsic luminescence lifetimes ranging from 0.228 to 21333 µs, based on luminescence, transient absorption measurements, X-ray diffraction, and calculations.

A boron-centered radical: a potassium-crown ether stabilized boryl radical anion.

A boron radical contact ion-pair Mes2B{4-(3,5-dimethylpyridinyl)}K(18-crown-6)(THF) (1K) has been isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy, UV-vis absorption spectroscopy and single crystal X-ray diffraction. The geometry, bonding and spin density distribution are shown to be affected by the NK interaction. The unpaired electron resides mainly on the boron atom and falls between those of triarylboron radical anions and neutral boron radicals. The work provides a novel boron-centered radical intermediate, connecting anionic and neutral boryl radicals.

Bipyridine hydrogel for selective and visible detection and absorption of Cd(2+).

Herein, we report for the first time the use of bipyridine-based hydrogel for selective and visible detection and absorption of Cd(2+). At low concentrations, hydrogelator 1 was applied for selective detection of Cd(2+) in vitro and in living cells with high sensitivity. In the absence of metal ions, 1 is nonfluorescent at 470 nm. Upon addition of metal ions, 1 selectively coordinates to Cd(2+), causing an 86-fold increase of fluorescence intensity at 470 nm via the chelation enhanced fluorescence (CHEF) effect, as revealed by first-principles simulations. At 1.5 wt% and pH 5.5, 1 self-assembles into nanofibers to form hydrogel Gel I. Since Cd(2+) could actively participate in the hydrogelation and promote the self-assembly, we also successfully applied Gel I for visible detection and absorption of Cd(2+). With these excellent properties, Gel I is expected to be explored as one type of versatile biomaterial for not only environmental monitoring but also for pollution treatment in the near future.