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Developing higher-energy-density and long-lifetime lithium-based batteries is essential for rapid energy delivery and recharging in emerging electric vehicles and grid energy-storage technologies. Anode-free lithium metal batteries (LMBs) possess an advanced cell configuration with only a bare anode metal foil current collector and no other negative electrode material that can maximize the energy density at the battery-pack level. However, capacity fading and operational safety risks caused by the formation of lithium (Li) dendrites impede the practical application of anode-free LMBs. Herein, we evaluated the growth of Li dendrites on an iron (Fe) substrate surface by performing a series of systematic molecular dynamics (MD) simulations based on the embedded-atom method (EAM) force field to investigate the effects of multiple surface morphologies on the Li atomic deposition and Li dendrite self-healing processes. The kinetics of Li dendrite growth on the atomic scale demonstrate that selecting the Fe(111) surface lattice orientation, reducing undesirable surface cracks, and controlling the surface nanogroove structures can be applied to effectively prevent the formation of irreversible Li dendrites on the surface of the Fe collector, resulting in better battery cell cycling. This work indicates that understanding the mechanism of Li growth on metal surfaces to search for an anode current collector that can significantly improve cell cycling stability is crucial for developing new anode-free LMBs. [ABSTRACT FROM AUTHOR]

A new carbon allotrope, cyclo[16]carbon (C16), has recently been successfully synthesized. It is hypothesized to exhibit double antiaromatic properties owing to the 4n π electrons. Theoretical calculations are a feasible method for systematically studying the structures and properties of unstable antiaromatic molecules. The results show that C16 has a planar structure characterized by alternating long and short bonds with D8h, and a strong antiaromatic characteristic originates from the two perpendicular π systems. We performed an extensive comparative analysis of C16 and the aromatic cyclo[18]carbon, C18. This study offers valuable insight into the structural and electronic characteristics of C16 and could inspire innovative applications and avenues for its utilization in various fields. [ABSTRACT FROM AUTHOR]

Monitoring early-stage β-amyloid (Aβ) dimerization is a formidable challenge for understanding neurological diseases. We compared β-sheet formation and histidine site-specific two-dimensional infrared (2D IR) spectroscopic signatures of Aβ dimers with different histidine states (δ; Nδ1–H, ε; Nε2–H, or π; both protonated). Molecular dynamics (MD) simulations revealed that β-sheet formation is favored for the δδδ:δδδ and πππ:πππ tautomeric isomers showing strong couplings and frequent contacts between the central hydrophobic core and C-terminus compared with the εεε:εεε isomer. Characteristic blue-shifts in the 2D IR central bands were observed upon monomer-dimer transformation. The εεε:εεε dimer exhibited larger frequency shifts than δδδ:δδδ and πππ:πππ implying that the red-shift may have a correlation with Nδ1–H(δ) protonation. Our results support the tautomerization/protonation hypothesis that attributes Aβ misfolding to histidine tautomers as a possible primary initiator for Aβ aggregation and facilitates the application of histidine site-specific 2D IR spectroscopy for studying early-stage Aβ self-assembly. [ABSTRACT FROM AUTHOR]

Compared to the p–n junction photovoltaic effect, the bulk photovoltaic effect is a potential way to overcome the external limitations of solar energy conversion. It is challenging to find new materials with a bulk photovoltaic effect. In this article, using first-principles calculations and the maximum local Wannier function, we investigated the bulk photovoltaic effect in GaNGeC quaternary compound semiconductors with six different crystal structures (S-1, S-2, S-3, S-4, S-5, and S-6 for short). These semiconductors showed a large effective three-dimensional shift current conductivity, where the maximum absolute value of the shift current conductivity ranges from 10 μA V−2 to 425 μA V−2, indicating that they are promising candidates for photoelectric conversion applications. Furthermore, the electron localization function, difference charge density, and atomic configurations as well as Löwdin population analysis revealed that dimerization of the GaN layer and the GeC layer in S-5 and S-6 induces delocalization of electrons. This delocalization of electrons enhances their shift current conductivities, which provides valuable insight for further design and development of new photovoltaic materials. [ABSTRACT FROM AUTHOR]

Sufficiently strong molecular magnets are used in small modern electronic and spintronic devices. Diradical organic magnetic molecules (OMMs) are promising options due to their lightness, flexibility, and the low energy required for their synthesis. In this field, the coupler is a dominating component, though acetylene, the shortest coupler, has not been studied for this use. In this study, we conceptualize several model systems using an acetylene link to couple different monoradicals. We simulated their magnetic strength using the broken symmetry method via density functional theory calculations. Our results show that the acetylene (–C≡C–) coupler gives much larger J values than the ethylene (–C＝C–) coupler. Acetylene coupling a phenoxyl (PO) and a nitronyl nitroxide (NN) diradical is the strongest ferromagnetic diradical OMM, and acetylene coupling a PO bisradical is the strongest anti-ferromagnetic diradical OMM. Moreover, we found that the magnetic strength is dependent on the coupler length and torsion, but is independent of the bending. Since only a very small energy barrier is needed, it is feasible to use torsion to tune a diradical OMM's magnetic strength. Our results are also beneficial for the rational design and synthesis of diradical OMMs. [ABSTRACT FROM AUTHOR]

The accumulation of ΔK280 tau mutant resulting in neurotoxic oligomeric aggregates is an important but yet mysterious procedure in Alzheimer's disease (AD) development. Recently, we proposed a histidine tautomerization hypothesis of tau fibrillogenesis for the pathobiology of AD and other neuro diseases. However, the influence of neutral histidine tautomeric states on tau mutation is still unclear. Herein, we performed replica-exchange molecular dynamics (REMD) simulations to characterize structural features as well as the mode of toxic action of the ΔK280 tau mutant in the presence of histidine tautomerism. Molecular dynamics (MD) simulation results show that the δε tautomeric isomer (having a distinct global energy minimum) had the highest β-sheet structure, which adopts a sheet-rich conformer and may have significant influence on the structural behaviors of ΔK280 tau monomers. Furthermore, clustering, residual contact map, mobility and structural analysis exhibited that the presence of β-strand interactions between stable lysine 8 (K8)–asparagine 13 (N13) and valine 39 (V39)–tyrosine 43 (Y43) residues plus K31–histidine 32 (H32) and K8–N13 (strand-loop-strand [β-meander] structure) helped δε to form toxic aggregates. Moreover, H299 played a more critical role in the conformational instability of the δε than H268. Overall, the results obtained from this study may be used to arrest neurodegeneration in ΔK280 tau mutation carriers as well as increase the understanding of AD-related tau pathogenesis and strengthen the histidine tautomerism hypothesis of misfolded peptide accumulation. [ABSTRACT FROM AUTHOR]

Nitrogen doped carbon functionalized CoSe2 nanowires (CoSe2@N–C NWs), which act as potential oxygen evolution reaction (OER) catalysts with a large current density and high stability have been reported. Owing to the collaborative optimization of electrical conductivity, free adsorption energy and binding strength of OER intermediates, the prepared CoSe2@N–C NWs exhibit an enhanced 6.61-fold catalytic activity compared to the pristine CoSe2 NW electrode in 1.0 M KOH solution at the overpotential of 340 mV. [ABSTRACT FROM AUTHOR]

Nitrogen/fluorine doping of TiO2 nanoparticles (NPs) serves to play an important role with regard to visible light absorption and charge carrier dynamics. However, it is largely unknown how nitrogen/fluorine doping retards electron–hole recombination. We carried out density functional theory and nonadiabatic molecular dynamics to demonstrate that the dopant levels, formation energies, and charge carrier dynamics depend strongly on the doping site. N-doping introduces both a hole and an electron trap without the presence of oxygen vacancies, while F-doping introduces only an electron trap. Quantum dynamics simulations show that holes are trapped within several picoseconds; N-doped NPs requires longer hole-trapping time than F-doped NPs due to the presence of an extra hole trap originating from the N 2p state. Electrons are trapped at a longer time scale than holes. F-doped NPs required longer electron-trapping time due to more strongly localized electron densities than N-doped TiO2 NPs. In general, Nitrogen and fluorine doping suppressed electron–hole recombination compared to pristine NP. NPs doped at the tip domain showed different charge recombination pathways by passing several hole traps (N-doping) or by dual channel routes (F-doping). NPs doped at edge domains showed relatively shorter excited state lifetime due to greater electronic coupling between trapped holes and electrons. NPs with doping at the inside domain effectively suppressed charge recombination due to a moderate energy gap and a reduced propensity to electron/hole localization. The diverse charge recombination scenarios revealed by nonadiabatic molecular dynamics simulations provided guidelines for the rational design of nanoscale metal oxides for solar energy harvesting and utilization. [ABSTRACT FROM AUTHOR]

A series of Ir- and Pt-based blue phosphorescent materials were theoretically investigated by means of density functional theory (DFT) calculations to improve their chemical stability in the excited state. High energy splitting between the lowest triplet state (T1 state), generally a metal-to-ligand charge transfer state (3MLCT), and the triplet metal-centred state (3MC) can prohibit ligand dissociation and suppress the decomposition reaction from the 3MC state to the dissociated S0. Here, we suggest a new design strategy to improve the chemical stability of blue phosphorescent materials in the excited state. Introducing inter- and intra-ligand interactions in Ir and Pt complexes can dramatically increase the ΔE(3MC-T1) because attractive or repulsive couplings arising from intra- or inter-ligand interactions can effectively prevent the out-of-plane bending vibrational mode in Ir complexes and the ring deformation vibrational mode in Pt complexes. A ΔE(3MC-T1) values of 18.62 kcal mol−1 for an Ir complex and 22.86 kcal mol−1 for a Pt complex from the T1 energy were obtained while the T1 energy was maintained in the blue region. To the best of our knowledge, these are the highest ΔE(3MC-T1) values reported to date. We believe that the present research provides profound insights into the excited state chemical stability of deep blue phosphorescent materials that could be implemented to improve device lifetimes. [ABSTRACT FROM AUTHOR]

A microfluidic chip integrated with a microelectrode and a cathodic photoelectrochemical (PEC) biosensor for the ultrasensitive detection of non-small cell lung cancer cytokeratin fragments based on a signal amplification strategy was designed. The mechanism for signal amplification is developed based on the p–n junction of AgI/Bi2Ga4O9, with dissolved O2 as an electron acceptor to produce the superoxide anion radical (˙O2−) as the working microelectrode. By combining this with a novel superoxide-dismutase-loaded honeycomb manganese oxide nanostructure (SOD@hMnO2) as the co-catalyst signal amplification label, ˙O2− can be catalyzed by SOD via a disproportionation reaction to produce O2 and H2O2; then, hMnO2 is able to trigger the decomposition of H2O2 to generate O2 and H2O. Therefore, the increased O2 promotes the separation of electron–hole pairs via consuming more electrons, leading to an effective enhancement of the cathodic PEC behavior. Under optimum conditions, with the cytokeratin 19 fragments 21-1 (CYFRA 21-1) as the targeted detection objects, the microfluidic cathodic PEC biosensor chip exhibited excellent linearity from 0.1 pg mL−1 to 100 ng mL−1, with a detection limit of 0.026 pg mL−1 (S/N = 3). The exciting thing that this work offers is a new strategy for the detection of other important cancer biomarkers for disease diagnosis and prognosis. [ABSTRACT FROM AUTHOR]

Time-resolved circular dichroism signals (TRCD) in the X-ray regime can directly probe the magnitude and the direction of ring currents in molecules. The electronic ring currents in Mg-porphyrin, generated by a coherent superposition of electronic states induced by a circularly polarized UV pulse, are tracked by a time-delayed circularly polarized attosecond X-ray pulse. The signals are calculated using the minimal coupling Hamiltonian, which directly makes use of transition current densities. The TRCD signals obtained from the left and right circularly polarized light pump have opposite signs, revealing the direction of the ring current. Molecular aromaticity and its role in photochemical reactions such as ring opening or closure can be studied using this technique. [ABSTRACT FROM AUTHOR]

We introduce amphiphilic nanoplatelets (ANPLs) that not only have a nanoscale Janus platelet geometry, but can also induce complementary face-to-face interactions among Pickering emulsion droplets. We showed that the ANPLs with such high surface activity can be a promising colloid surfactant enabling smart rheology modification of complex emulsion fluids. [ABSTRACT FROM AUTHOR]

Graphyne materials are potential candidates to fabricate low-cost but efficient metal-free oxygen reduction reaction (ORR) electrocatalysts. However, due to the coexistence of sp and sp2 carbon atoms in graphyne, some factors playing important roles in determining the ORR activity have received little attention. In the present paper, we carried out thorough density functional theory (DFT) calculations to study the curvature effect on the ORR activity of γ-graphyne. Our results suggest that the (5, 0)-γGyNT would be an excellent metal-free ORR catalyst. Its limiting potential was computed to be 0.80 V and the corresponding active sites occupy up to 16.7% in content, much better than previously reported CACs. Moreover, it is revealed that the curvature can tune the degree of exposure of p electrons of active sites, thus tuning the ORR activity. Our findings are beneficial for further understanding catalytic behavior on graphyne related materials and we suggest a new strategy to design high performance metal-free ORR catalysts. [ABSTRACT FROM AUTHOR]

Organic magnetic materials must possess sufficient magnetic coupling to realise their potential. Most coupling studies were based on intramolecular modifications because the molecular structure ultimately dictates the molecule's properties. In this study, non-covalent interactions, specifically hydrogen bonding (HB), are explored as a strategy to enhance the magnetic coupling in a diradical. Model systems were conceptualised based on nitroxide (NO) and nitronyl nitroxides (NN) as spin centres (SCs) with an acetylene-bridged phenylene coupler. The combinations and orientations of SCs were chosen so that a ferromagnetic diradical would result, meaning two NOs are meta directionally oriented (mNO-NO) while NO and NN are in para positions (pNN-NO). Hydrogen-bonding was introduced to mNO-NO and pNN-NO using HX as HB donors (HX = HF, HCl, HBr, H2O, and NH3). HB interaction energies were calculated with relative strengths in the following order: HF > HCl > H2O ≈ HBr > NH3. Reduced density gradients (RDG) confirm the presence of HB and the relative strengths of HX varies incrementally. This justifies using them to investigate how the HB interaction energy influences diradical magnetic coupling. Magnetic coupling revealed through J values was found to have a linear dependence on the HB strength. An improved J value is associated with a decrease in total spin density values on major atom sites N and O. This work demonstrates the potential use of HB for further increasing the magnetic exchange in organic magnetic materials. Insights derived from this work can be used in the design of diradical aggregates. [ABSTRACT FROM AUTHOR]

By performing first-principles calculations, CO oxidation catalyzed by Fe-embedded defective α-graphyne was systematically investigated. It was found that Fe atoms were strongly anchored at the sp-C vacancy site of α-graphyne with a large binding energy of −5.28 eV and effectively adsorbed and activated O2 molecules. Then, we systematically compared CO oxidation by activated O2via Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms. The calculated potential energy surfaces show that the Fe-doped α-graphyne can efficiently oxidize CO via the ER mechanism, in which the threshold of the rate determining step is 0.77 eV. Furthermore, Fe doping shows little effect on the diffusivities of CO, O2, and CO2, which can further enhance its catalytic performance. [ABSTRACT FROM AUTHOR]

Mitochondrial enzyme monoamine oxidase (MAO-A) is known to be overexpressed in prostate cancer (PCa) cells. Herein, we have developed a two-photon probe (PCP-1) for selectively targeting and imaging the MAO-A in PCa. Supported by enzymatic docking and in vitro experiments, PCP-1 showed efficiency to visualize MAO-A overexpressing cells and inhibit their growth and metastasis potential. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) ReS2 is considered as a promising energy storage material owing to its high theoretical capacity and extremely weak van der Waals forces. However, the use of 2D ReS2 is limited by its low electrical conductivity, slow ion diffusion, and huge volume expansion. Herein, we demonstrate oxygen incorporation and interlayer expansion of ReS2 nanosheets deposited on hollow mesoporous carbon spheres. The oxygen content of 2D ReS2 is controlled by varying the reaction solvents and temperatures and thus, its interlayer spacing is expanded, which facilitates the redox kinetics by means of the improved electronic conductivity and rapid ion diffusion as demonstrated by computational calculation and electrochemical characterization. Moreover, a hollow mesoporous core/shell hybrid architecture contributes to a large accessible area and porous channels. The as-optimized hybrid electrodes with expanded interlayers and oxygen content achieve higher capacity and better rate and cycling capabilities than other samples. Therefore, this chemical strategy highlights the importance of controlling the interlayer spacing and chemistry of ReS2 to overcome the kinetic and stability limitations of 2D energy storage nanomaterials. [ABSTRACT FROM AUTHOR]

TiO2 photocatalysts have been widely used in the field of renewable energy and environmental clean-up. However, the large band gap of TiO2, along with the fast recombination of charge carriers, significantly lowers the photocatalytic performance. Many strategies have been developed to address this issue, including nanostructuring, introducing oxygen defects, chemical doping, surface sensitization, and employing nanocomposites. Studies of light absorption and especially charge recombination of modified TiO2 particles by experimental approaches are limited by the entangled parameters introduced by experimental conditions. Theoretical approaches have provided useful insight due to the systematic modelling of TiO2 particles. This review encompasses the theoretical approach to investigate the photocatalytic activity of modified TiO2 nanoparticles. The density functional theory (DFT) methods used to describe the properties of TiO2 systems and modelling of the geometric and electronic structure to properly describe the actual nanoparticles used in experiments are discussed. The chemical modification strategies are discussed in terms of band engineering, and charge carrier separation and diffusion in comparison with experimental results. The surface redox reactions are discussed with regard to thermodynamics and kinetics. [ABSTRACT FROM AUTHOR]

Vacancy defects are one of the key impurities that strongly affect the properties of materials. In the present study, some different double-atom vacancies were introduced into α-graphyne (Gy), βGy, and γGy, depending on their own structural characteristics. Subsequently, density functional theory (DFT) calculations were carried out to evaluate the changes in the structural and electronic properties induced by the double-atom vacancies. The results indicated that the double-atom vacancies only lead to an in-plane structural rearrangement of all three of the Gy systems. It was further revealed that the position of the double-atom vacancies is a crucial factor in the manipulation of the electronic properties of αGy and βGy as compared with γGy. Our work is expected to yield new Gy materials with the desired properties obtained by altering the position of induced double-atom vacancies. [ABSTRACT FROM AUTHOR]

Cross-conjugated molecules are an interesting class of conjugated systems possessing a spatially separated HOMO and LUMO. Most previous studies have taken advantage of this property by using it in organic semiconductor applications. Herein, we undertake a new investigation on the use of this type of molecule, in particular benzo[1,2-d;4,5-d′]bisoxazole (BBO), as a coupler for organic diradicals. BBO has two sites available for adding a substituent and a spin center (SC) which are along its 4,8- and 2,6-axes. Functionalizations using electron donating (ED) and electron withdrawing (EW) groups were imposed to tune its FMOs and it was found that the longer 2,6-axis is an ideal site with a broader LUMO range via substituent effects. Diradicalization of these BBOs using nitronyl nitroxide (NN) and nitroxide (NO) as SCs was done using the remaining available axis. The calculated J values are linearly dependent on the LUMO energy of the coupler, but with 4,8-NH2-2,6-SC as an outlier. This exceptional case is related to 4,8-NH2-2,6-SC having the lowest BBO-NN dihedral angle. Moreover, the diradicals 4,8-X-2,6-SC (with X = H, NH2, CH3) have higher J values than 2,6-X-4,8-SC (with X = H, NH2, CH3), which is counterintuitive because the latter have a shorter coupling path. These diradicals are positioned to the right of the intersection of their trend lines, which implies that diradicals with LUMO values to the right of this intersection have the tendency to attain J values that are higher than those diradicals with a shorter coupling path. 4,8-NH2-2,6-SC even surpasses the projected JMax values which we associate with the highest attainable J values due to LUMO tuning via substituent effects. These results provide useful insights, especially into the interplay between the LUMO and the dihedral angle and how these affect magnetism in diradicals. In conclusion, we found that BBO can be a good candidate as an effective coupler for diradicals with tunable J values via incorporation of ED and EW groups. This first approach to studying the application of cross-conjugated molecules as couplers also paves the way for new candidates for the development of more effective diradical systems. [ABSTRACT FROM AUTHOR]

Hollow and microporous organic network bearing alkynone moieties was prepared via carbonylative Sonogashira coupling. The carbonyl groups in the network showed unusual chemical reactivities, compared with those of a model alkynone compound. The observed differences between the reactivities of alkynones in the molecule and in the network were analyzed based on the “network effect”. [ABSTRACT FROM AUTHOR]

Electrical control of magnetic exchange coupling interactions is central to designing magnetic materials. In this study, we performed density functional theory calculations to investigate the magnetic spin configuration, magnetic moment, and magnetic coupling strength of zigzag MoS2 nanoribbons (zMoS2NRs) with different edge passivation, that is, pristine (Pristine), hydrogen termination (H-tem), sulfur termination (S-term), and sulfhydryl termination (SH-term). Further, we investigated the influence of an external electric field (FExt) on the magnetic properties. Pristine and H-term showed an AFM ground configuration with considerably weak magnetic coupling strength while S-term and SH-term showed a single edge FM ground configuration in the absence of the electric field. When the external electric field was applied, the positive field intensified the original spin configuration, thus increasing the magnetic moment of the system while the negative field weakened the original spin configuration, thus decreasing the magnetic moment and further reversed the spin configuration from AFM to FM and vice versa in most systems. The magnetic coupling strength of the system increased for both Pristine and H-term regardless of the direction of the field. However, the extent of increase was much higher in Pristine due to the existence of relatively easily transferable dangling electrons compared with the constrained electrons of H-term restricted to chemical bonds. Our results demonstrate a possibility of reversible spin control from AFM to FM and vice versa by applying an electric field and the enhancement of the magnetic coupling strength of zMoS2NRs. [ABSTRACT FROM AUTHOR]

Electronic structures of zigzag (n,0), armchair (n,n), and chiral (n,m) α-graphyne nanotubes (αGNTs) with n = 2–7 were investigated using density functional tight binding calculations. Oscillatory behavior of the band gaps with a period of every (n−m) = 3 was found for each tube. According to the periodicity, αGNTs could be classified into three families, and their band gaps were in the increasing order of (n−m) = 3a ＜ 3a + 1 ＜ 3a + 2. Among the three families, αGNTs with (n−m) = 3a became effectively semimetallic when the tube size was larger than approximately 2 nm, while the other families remained semiconducting. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2), as a semiconductor metal oxide, has been one of the most popular materials studied in the field of photocatalysis. In the present study, the properties of single oxygen vacancies of (TiO2)35, a prototype of an anatase nanoparticle, were investigated by DFT calculations. (TiO2)35 is the minimum sized model (∼2 nm) for a bipyramidal nanoparticle with anatase phase and eight {101} facets. All the available oxygen vacancies at various sites according to position, coordination number, and distance from the center atom were examined. The geometric, energetic and electronic properties of the reduced TiO2 clusters were analyzed by hybrid DFT functionals with different Hartree–Fock exchange ratios (0, 12.5 and 25%). It was found that the structure of pristine (TiO2)35 is somewhat different from the bulk lattice, with a relatively high surface to volume ratio. Moreover, the particular highly (three)-coordinated oxygen atom is energetically the most favorable for oxygen vacancy formation from the nanoparticle mainly due to its substantially high relaxation energy. TiO2 nanoparticles have low oxygen vacancy formation energy and narrow band gap because of their defect states, and can be utilized as an efficient photocatalyst material. [ABSTRACT FROM AUTHOR]

A coumarin based Schiff base was found to be an excellent indicator of moisture, via rapid in situ hydrolysis. A structure-relationship examination of a small library of Schiff bases revealed the critical importance of hydrogen bond acceptors in close proximity to the imine bond, and this observation was further supported by theoretical calculations as well as the solid state structure analysis. The most sensitive compound demonstrated a limit of detection and quantification of 0.18% and 0.54% v/v water in DMSO, respectively. [ABSTRACT FROM AUTHOR]

Hollow microporous organic networks bearing isocoumarin moieties (H-IC-MONs) were prepared via a tandem synthetic approach. Pd catalysts conducted the networking of building blocks by the Sonogashira coupling with the concomitant generation of isocoumarins through cyclization. The H-IC-MONs showed visible light absorption and emission properties and were applied to nitrophenol sensing using visible light. [ABSTRACT FROM AUTHOR]

Conventional density functionals with either the local density approximation (LDA) or the generalized gradient approximation (GGA) form of the exchange–correlation potential fail to describe the electronic structure of a large number of metal oxides. Both the LDA and the GGA grossly underestimate the band gaps of these materials which severely affect the description of oxygen vacancy point defect states in reduced samples. To find a pragmatic approach to simultaneously and accurately describe the atomic and electronic structures of the most common TiO2 polymorphs, we explore the effect of the percentage of exact, non-local, Fock exchange on the electronic structure of stoichiometric rutile and anatase. From these results, a modified hybrid functional is proposed to properly describe the atomic structures, formation enthalpies and electronic structures of rutile and anatase and, at the same time, the results of reduced samples are also in good agreement with the available experimental results. The present approach can be safely used to accurately describe numerous TiO2 based materials containing defects or realistic nanoparticles for which the required large unit cells or system sizes hinder the use of GW related techniques. [ABSTRACT FROM AUTHOR]

Three new heteroleptic Ir(iii) complexes o-LIrpic, m-LIrpic, and p-LIrpic (L = CF3DPQ) consisting of 2,4-diphenylquinoline (DPQ) with a –CF3 group at ortho (o)/meta (m)/para (p) positions of the metalated phenyl ring, respectively, as the main ligands were synthesized and used as emitters in phosphorescent organic light-emitting diodes (PhOLEDs). We realized that –CF3 position extremely affects the crucial photophysical and electronic properties such as emission color, photoluminescence quantum yield (PLQY) and energy levels of these Ir(iii) complexes resulting in –CF3 position-dependent performance of their PhOLEDs. To verify the effect of –CF3 group position on device performance, three other Ir(iii) complexes o-LIrtmd, m-LIrtmd, and p-LIrtmd were synthesized using the same main ligands but a different ancillary ligand. In the two series of Ir(iii) complexes, the devices with m-CF3 based complexes are outstanding in performance compared to o- or p-CF3 based ones due to the enhanced PLQY and well suppressed non-radiative deactivations by m-substitution. Finally, the single emission layer solution-processed orange and two-component white PhOLEDs fabricated using m-LIrpic as orange emitter achieved the maximum external quantum efficiency of 17.1% (43.9 cd A−1) and 21.1% (48.8 cd A−1), respectively, with highly stable color coordinates and low efficiency roll-off. This is the highest efficiency reported to date for solution-processed orange PhOLEDs using a small molecular host with easily accessible emitter. [ABSTRACT FROM AUTHOR]

Sn–porphyrin networks were engineered on the surface of a thin layer chromatography (TLC) plate via Sonogashira coupling of the Sn–porphyrin building block and 1,4-diiodobenzene. The Sn–porphyrin film showed a strong Soret band absorption at 422 nm, emission at 600–630 nm, and excellent sensing performance toward nitrophenols in water. [ABSTRACT FROM AUTHOR]

π-spacers and alkyl side chains play a key role in the optical, electrochemical, and photovoltaic properties of π-conjugated polymers. To investigate the collective effects of π-spacers, alkyl side chains, and various processing conditions on the photovoltaic properties, an array of four new low bandgap (LBG) π-conjugated polymers (P1–P4) was designed and synthesized for their application as donor materials in bulk heterojunction polymer solar cells (BHJ PSCs). These π-conjugated polymers contain a benzodithiophene (BDT) donor unit substituted with 2-ethylhexylselenyl or 2-hexyldecylselenyl as π-conjugated side chains and a dialkoxybenzothiadiazole (dialkoxyBT) electron deficient unit connected with thiophene or selenophene as π-spacers. Among the four polymers, the absorption spectra of P3 with the thiophene π-spacer showed a well enhanced vibronic shoulder peak between 620 and 650 nm, indicating that P3 possesses a strong interchain aggregation tendency and attains a planar backbone structure due to the non-covalent interactions arising between the sulfur atom in thiophene and the oxygen atom in dialkoxyBT. Under suitable device processing conditions optimized pristine PSCs of P3 showed a maximum power conversion efficiency (PCE) of 4.09%. After employing 1,8-diiodooctane as an additive, one of the PSC devices based on P2 displayed a PCE of 5.34%. The active layers of P1–P4 showed a positive response towards methanol treatment, especially the P3-based devices delivered an improved PCE of 5.63%, which was further assessed by electrical impedance spectroscopy. These findings in the current article provide a good specimen for efficiently fine tuning the optical and photovoltaic properties of π-conjugated polymers via varying the size of alkyl chains, π-spacer groups and device processing conditions for the imminent growth of LBG π-conjugated polymers. [ABSTRACT FROM AUTHOR]

This work shows that microporous organic network (MON) chemistry can be successfully applied for the development of a visible light-induced hydrogen production system. A visible light harvesting MON (VH-MON) was prepared by the Knoevenagel condensation of tri-(4-formylphenyl)amine with [1,1'-biphenyl]-4,4'-diacetonitrile. Scanning electron microscopy (SEM) showed a 1D rod morphology of the VH-MON. Analysis of a N[sub 2] sorption isotherm showed a 474 m[sup 2] g[sup -1] surface area and microporosity. Solid phase [sup 13]C nuclear magnetic resonance (NMR) and infrared (IR) absorption spectroscopy, and elemental analysis support the expected network structure. The VH-MON showed visible light absorption in 400-530 nm and vivid emission at 542 nm. The HOMO and LUMO energy levels of the VH-MON were simulated at -5.1 and -2.4 eV, respectively, by density functional theory (DFT) calculation. The VH-MON/TiO[sub 2]-Pt composite exhibited promising activity and enhanced stability as a photocatalytic system for visible light-induced hydrogen production from water. [ABSTRACT FROM AUTHOR]

Graphyne is a rising two-dimensional (2D) carbon allotrope with excellent electronic properties. In this paper, theoretical calculations were performed to study the corresponding electronic properties of the oxygenated graphyne. Atomic oxygen when bound to the carbon atom of graphyne forms a stable oxide, with a much larger binding energy compared to that on graphene. Owing to the oxygen adsorption, the α- and β-graphyne change from a zero-band-gap material to a semiconductor as indicated in the band structure calculations. Moreover, spin splitting was observed from the band structure of the oxygenated γ-graphyne. These electronic properties are tunable by altering the oxygen coverage through changing the supercell size. Our results based on the first-principles calculations imply that oxygenation is a promising method to functionalize graphyne to achieve designated properties. [ABSTRACT FROM AUTHOR]

Polydiacetylenes (PDAs), a family of conjugated polymers, are known to show stimulus-induced apparent blue-to-red transitions, which have led to the development of a variety of PDA-based chemosensors. However, in most cases, recognition sites were introduced at the terminal ends of PDAs, therefore, recognition processes on the surface of PDAs have been the primary stimulations to induce blue to red colorimetric changes. In this study, we reported that diverse colorimetric changes can be observed for PDA based sensors in which penetration of cationic surfactant into PDAs bearing benzoic acid groups can cause not only the typical blue to red change but also blue to violet, blue to yellow or blue to orange color change. We systematically demonstrated that these novel findings can be used effectively to discriminate different cationic surfactants by using three different PDAs. Furthermore, theoretical calculations and transmission electron microscope (TEM) images also confirm these unique colorimetric changes. These results suggest a new direction in which to design colorimetric sensors based on PDA polymers. [ABSTRACT FROM AUTHOR]

Hydrogelation of a pyridine derivative (1) possessing tetrazole moieties as end groups, without long alkyl chain groups, results in the formation of a Mg(NO3)2coordination polymer gel. The polymer exhibits a strong fluorescence enhancement upon gel formation. 1can also be gelated with a variety of magnesium anions such as SO42−, NO3−, Cl−, Br−and I−, indicating that the coordination polymer gel formation of 1does not strongly depend on anions. The SEM and AFM images of Mg2+coordination polymer gel 1display a fibrillar network several micrometres long, with widths in the range of 60–70 nm and thicknesses of about 3 nm. In addition, photophysical studies show that the hydrogel exhibits a typical π–π* transition and gives rise to high fluorescence behavior. The coordination polymer hydrogel exhibits viscoelastic behavior as evidenced from the rheological studies. [ABSTRACT FROM AUTHOR]

We have studied the solvent effect on structures and potential energy surfaces along proton transfer in the ground and the excited states of 7-hydroxyquinoline interacting with an ethanol dimer using ab initiocalculations. The proton transfer is forbidden in the ground state not only in vacuum but also in solvents of n-heptane, ethanol, and dimethyl sulfoxide. In the excited state, although the proton transfer is forbidden in vacuum, it is possible in solvent due to its greatly reduced barrier (∼10 kcal mol−1) and highly stabilized product. It has also been found from the calculations that the proton-transfer barrier in the excited state decreases as the dielectric constant of a solvent increases. Our calculations are consistent with experimental results that the proton transfer does not take place in the ground state and that the excited-state proton-transfer rate increases as the solvent polarity increases. Our calculated absorption and emission properties are in excellent agreement with experimental results. Projection factors (reflecting geometrical change from the ground state to the excited state) and reorganization energies for several low frequency vibrations in connection with the excited-state proton transfer are discussed as well. [ABSTRACT FROM AUTHOR]

We report a nonvolatile memory organic field effect transistor (OFET) using ambipolar organic molecules as nano-interfaced semiconductor materials. Newly synthesized push-pull organic molecules (PPOMs) containing triarylamine as an electron donating group, thiophene as a spacer, and malononitrile as an electron withdrawing group are proposed. The tilted PPOMs with side chains could control the charge trapping of the conducting channel formed between pentacene and PPOMs. Quantum chemical calculations were carried out to estimate the dihedral angle at the neutral and electron charged anion molecules and to explain the charging effects for the memory OFET performance (write-read-erase-read cycles). The charge mobilities of OFETs comprising the nano-interfaced PPOMs were affected by the dihedral angles derived from the steric hindrance of the bulky side chain of the spacer. The memory OTFT with higher dihedral angle material exhibited a wider memory window as well as reduced current flow. The memory OFET devices showed a memory window of −40 to +40 V, a memory ratio of 100 for “ON” to “OFF” currents, and long retention time for the nonvolatile memory. [ABSTRACT FROM AUTHOR]

A new tetranaphthoimidazolium receptor was synthesized and reported to be a selective fluorescent chemosensor for phytate, myo-inositol hexakisphosphate (IP6). In a 100% aqueous solution at pH 7.4, chemosensor 1 showed a selective fluorescence enhancement for IP6 over IP3, phosphates, pyrophosphates, AMP, ADP and ATP. An excimer emission at 465 nm linearly increases in the range of 300 nM to 1 μM with a detection limit of 2.28 × 10−7 M. In addition, first live cell imaging of IP6 has been demonstrated by using a synthetic receptor. [ABSTRACT FROM AUTHOR]

An oxadiazole based electron transporting (ET) unit was glued to the heteroleptic Ir(iii) complex (TPQIr-ET) and used as a dopant for phosphorescent organic light-emitting diodes (PhOLEDs). It shows superior device performance than the dopant without the ET unit (TPQIr) due to the balanced charge carrier injection by the ET unit. [ABSTRACT FROM AUTHOR]