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Incorporating functionalized TiO2 microarchitectures or upconversion nanoparticles (UCNPs) into photoanodes is deemed to be two effective ways to boost the photovoltaic performance of dye-sensitized solar cells (DSSCs). Nonetheless, studies combining functionalized TiO2 and UCNPs for the development of composite photoanode films in DSSCs still remain scarce. In view of this, we present a facile strategy for the design and preparation of a multifunctional composite photoanode containing P25 nanoparticles, peanut-like (PN) TiO2 microstructures, and NaYF4:Yb,Er@NaYF4:Nd@SiO2 core–shell–shell UCNPs. It is found that the DSSC containing a dual-functional photoanode using PN TiO2 as a light-scattering layer and P25 as a transparent layer can achieve a photovoltaic efficiency of 9.01%, presenting a 26.37% enhancement over the blank device. More importantly, the addition of UCNPs can further enhance the photoelectric performance of the DSSC device, realizing an optimal photovoltaic efficiency of 10.58%, one of the highest reported efficiencies for UCNP-based DSSCs with the common N719 photosensitizer. Such a remarkable improvement is mainly due to a synergetic effect of the UCNPs absorbing the near-infrared light and of the PN TiO2 presenting excellent light-scattering potency. Specifically, steady-state experiments reveal that the best-performing device shows only a small efficiency loss after 120 h of testing, exhibiting good device stability. The present work demonstrates the importance of composite photoanodes in enhancing the photovoltaic performances of solar cells. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloy is an extremely excellent structural material, and the improvement of its mechanical properties has attracted extensive attention. However, there is still lack of a systematical study that considers various types of Mg alloys and versatile mechanical performance. In this paper, extensive and in-depth machine learning (ML) research is carried out on the four mechanical properties of Mg alloys, including ultimate tensile strength (UTS), elongation (EL), yield strength (YS) and hardness (HV). By collecting experimental data in the published literatures, the mechanical properties database of Mg alloy was established. The experimental parameters, basic properties and thermodynamic parameters of alloys are used as descriptors to construct the ML models thus predicting the four mechanical properties of Mg alloys. In the total dataset and the cast and extrusion subsets, the optimum prediction models for UTS, YS, and HV achieved high accuracy, with the values of coefficients of determination above 0.8 and a maximum value of 0.93 in the test set, although the prediction model of EL was not satisfactory. In addition, the machine learning model is interpreted by using the Shapley additive explanations (SHAP) model, and the critical values of important descriptors affecting the mechanical properties are obtained, especially the range of feature values that can improve YS and EL at the same time, which is of great significance for the development of the mechanical properties in the design of high-performance Mg alloys. [ABSTRACT FROM AUTHOR]

The conversion of nitrogen–oxygen-rich biomass wastes into heteroatomic co-doped nanostructured carbons used as energy storage materials has received widespread attention. In this study, an in situ nitrogen–oxygen co-doped porous carbon was prepared for supercapacitor applications via a two-step method of pre-carbonization and pyrolytic activation using mixed egg yolk/white and rice waste. The optimal sample (YPAC-1) was found to have a 3D honeycomb structure composed of abundant micropores and mesopores with a high specific surface area of 1572.1 m2 g−1, which provided abundant storage space and a wide transport path for electrolyte ions. Notably, the specific capacitance of the constructed three-electrode system was as high as 446.22 F g−1 at a current density of 1 A g−1 and remained above 50% at 10 A g−1. The capacitance retention was 82.26% after up to 10,000 cycles. The symmetrical capacitor based on YPAC-1 with a two-electrode structure exhibited an energy density of 8.3 Wh kg−1 when the power density was 136 W kg−1. These results indicate that porous carbon materials prepared from mixed protein and carbohydrate waste have promising applications in the field of supercapacitors. [ABSTRACT FROM AUTHOR]

Sustainable and high-performance energy storage materials are crucial to address global energy and environmental challenges. In this study, Spirulina platensis was used as the carbon and nitrogen source, and Spirulina-based nanoporous biochar (SNPB) was synthesized through chemical activation using KOH as the activating agent in N2 atmosphere. SNPB-800-4 was characterized by N2 adsorption–desorption and XPS, showing a high specific surface area (2923.7 m2 g−1) and abundant heteroatomic oxygen (13.78%) and nitrogen (2.55%). SNPB-800-4 demonstrated an exceptional capacitance of 348 F g−1 at a current density of 1 A g−1 and a remarkable capacitance retention of 94.14% after 10,000 cycles at a current density of 10 A g−1 in 6 M KOH. Notably, symmetric supercapacitors SNPB-800-4//SNPB-800-4 achieved the maximum energy and power densities of 17.99 Wh kg−1 and 162.48 W kg−1, respectively, at a current density of 0.5 A g−1, and still maintained 2.66 Wh kg−1 when the power density was increased to 9685.08 W kg−1 at a current density of 30 A g−1. This work provides an easily scalable and straightforward way to convert waste algae biomass into in situ N, O-dually doped biochar for ultra-high-power supercapacitors. [ABSTRACT FROM AUTHOR]

We report a new strategy to fabricate a multifunctional composite photoanode containing TiO2 hollow spheres (TiO2‐HSs), Au nanoparticles (AuNPs) and novel NaYF4 : Yb,Er@NaLuF4 : Eu@SiO2 upconversion nanoparticles (UCNPs). The AuNPs are grown on the photoanode film including TiO2‐HSs and UCNPs by a simple in situ plasmonic treatment. As a result, an impressive power conversion efficiency of 14.13 % is obtained, which is a record for N719 dye‐based dye‐sensitized solar cells, demonstrating great potential for the solar cells toward commercialization. This obvious enhancement is ascribed to a collaborative mechanism of the TiO2‐HSs exhibiting excellent light‐scattering ability, of the UCNPs converting near‐infrared photons into visible photons and of the AuNPs presenting outstanding surface plasmon resonance effect. Notably, a steady‐state experiment further reveals that the champion cell exhibits 95.33 % retainment in efficiency even after 180 h of measurements, showing good device stability. [ABSTRACT FROM AUTHOR]

We report a new strategy to fabricate a multifunctional composite photoanode containing TiO2 hollow spheres (TiO2‐HSs), Au nanoparticles (AuNPs) and novel NaYF4 : Yb,Er@NaLuF4 : Eu@SiO2 upconversion nanoparticles (UCNPs). The AuNPs are grown on the photoanode film including TiO2‐HSs and UCNPs by a simple in situ plasmonic treatment. As a result, an impressive power conversion efficiency of 14.13 % is obtained, which is a record for N719 dye‐based dye‐sensitized solar cells, demonstrating great potential for the solar cells toward commercialization. This obvious enhancement is ascribed to a collaborative mechanism of the TiO2‐HSs exhibiting excellent light‐scattering ability, of the UCNPs converting near‐infrared photons into visible photons and of the AuNPs presenting outstanding surface plasmon resonance effect. Notably, a steady‐state experiment further reveals that the champion cell exhibits 95.33 % retainment in efficiency even after 180 h of measurements, showing good device stability. [ABSTRACT FROM AUTHOR]

Developing metal‐nitrogen‐carbon (M‐N‐C)‐based single‐atom electrocatalysts for carbon dioxide reduction reaction (CO2RR) have captured widespread interest because of their outstanding activity and selectivity. Yet, the loss of nitrogen sources during the synthetic process hinders their further development. Herein, an effective strategy using 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM][BF4]) as a liquid nitrogen source to construct a nickel single‐atom electrocatalyst (Ni‐SA) with well‐defined Ni‐N4 sites on a carbon support (denoted as Ni‐SA‐BB/C) is reported. This is shown to deliver a carbon monoxide faradaic efficiency of >95% over a potential of −0.7 to −1.1 V (vs reversible hydrogen electrode) with excellent durability. Furthermore, the obtained Ni‐SA‐BB/C catalyst possesses higher nitrogen content than the Ni‐SA catalyst prepared by conventional nitrogen sources. Importantly, only thimbleful Ni nanoparticles (Ni‐NP) are contained in the large‐scale‐prepared Ni‐SA‐BB/C catalyst without acid leaching, and with only a slight decrease in the catalytic activity. Density functional theory calculations indicate a salient difference between Ni‐SA and Ni‐NP in the catalytic performance toward CO2RR. This work introduces a simple and amenable manufacturing strategy to large‐scale fabrication of nickel single‐atom electrocatalysts for CO2‐to‐CO conversion. [ABSTRACT FROM AUTHOR]

Magnesium (Mg)‐ion batteries with low cost and good safety characteristics has attracted a great deal of attention recently. However, the high polarity and the slow diffusion of Mg2+ in the cathode material limit the development of practical Mg cathode materials. In this paper, an anion‐rich electrode material, NiS2, and its composite with Ni‐based carbon nanotubes (NiS2/NCNTs) are explored as the cathode materials for Mg‐ion batteries. These NiS2/NCNTs with excellent Mg2+ storage property is synthesized by a simple in situ growth of NiS2 nanoparticles on NCNTs. NiS2 with both a large regular cavity structure and abundant sulfur‐sulfur (SS) bonds with high electronegativity can provide a large number of active sites and unobstructed transport paths for the insertion–disinsertion of Mg2+. With the aid of 3D NCNTs skeleton as the transport channel of the electron, the NiS2/NCNTs exhibit a high capacity of 244.5 mAh g−1 at 50 mA g−1 and an outstanding rate performance (94.7 mAh g−1 at 1000 mA g−1). It achieves capacitance retention of 58% after 2000 cycles at 200 mA g−1. Through theoretical density functional theory (DFT) calculations and a series of systematic ex situ characterizations, the magnesiation/demagnesiation mechanisms of NiS2 and NiS2/NCNTs and are elucidated for fundamental understanding. [ABSTRACT FROM AUTHOR]

A new photocatalyst was synthesized by a combination of the upconversion nanoparticle NaYF4:Yb, Tm, Gd (NYTG) and NH2-MIL-101(Cr) (NMC) to form NYTG/NMC. The heterostructure exhibited great stability and excellent photocatalytic activity through utilization of the wide spectrum from the near-infrared (NIR) to the UV-vis range. Compared with NMC, the photocatalytic performance was increased by 22% for rhodamine B (RhB) with the most suitable amount of Gd3+ ions and the ratio between NYTG and NMC. This could be attributed to the doped Gd3+ ions refining the crystallinity and hexagonal phase of NaYF4 by replacing the Y3+ ions, leading to an enhanced emission intensity along with an increased number of emitted peaks in the UV-vis region. The enhanced photocatalytic performance of NYTG/NMC was also related to the synergistic effects of the individual components, which facilitate the separation of electrons and holes. On the basis of scavenging experiments, the possible mechanism for photocatalytic degradation is proposed to uncover more clues for the further designs of new photocatalysts. This work suggests a pathway to enhance the emission intensity by refining the structure rather than by developing a core–shell structure. [ABSTRACT FROM AUTHOR]

The addition of coadsorbents and the introduction of electron-withdrawing groups in dye sensitizers are considered feasible strategies for improving the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). However, facile and precise predictions of the influence of these two strategies on their photovoltaic properties, including PCE, are challenging. In this contribution, we studied a known D–A–π–A indoline dye WS-2 adsorbed on a TiO2 anode represented by a supercell model. The PCE of this dye was evaluated to be between 9.69% and 13.70%, depending on the supercell representation, compared with an experimental value of 8.55%. The PCE could be increased to 16.39% on a moderate supercell by adding chenodeoxycholic acid (CDCA) as a coadsorbent. Such an enhancement could be ascribed to the intermolecular interaction between WS-2 and CDCA, suppressing excessively high dye coverage and thereby resulting in a remarkable increase in the open-circuit voltage. Based on WS-2, a new molecule WS-2a was rationally designed by substituting the benzothiadiazole moiety of WS-2 with a stronger electron-withdrawing thienyl-diketopyrrolopyrrole group. Consequently, the maximum absorption band showed a large red-shift from 522 to 638 nm, broadening the spectral response into the near-infrared region. A higher PCE of 16.62% was obtained for WS-2a. Moreover, the coadsorption of WS-2a and CDCA onto the TiO2 supercell achieved the best photovoltaic efficiency with a value as high as 24.15%. Therefore, the present study quantitatively reveals the impact of the coadsorbent and electron-withdrawing groups on the optoelectronic properties of dyes, which opens a new avenue to design high-efficiency D–A–π–A-structured organic sensitizers for promising DSSC applications. A discussion on the qualification of these results is given. [ABSTRACT FROM AUTHOR]

Ground-state geometries of carbenes H2Cn (n = 3-10) have been fully optimized with the C2ν-symmetry constraint at the density functional theory and restricted-spin coupled-cluster single-double plus perturbative triple excitation levels of theory, respectively. Comparison of structures corresponding to the X1A1 and B1B1 electronic states has been made by the complete active space self-consistent field calculations. Parity alternation effect on various properties of the ground-state geometries has been discovered in the present study, which generally gives illustration for the relative stabilities of the titled carbon chains. Further calculations on their electronic spectra have been carried out by means of the complete active space second-order perturbation theory method along with the cc-pVTZ basis set. It is found that the vertical excitation energies of the dipole-allowed B1B1 ← X1A1 transition in the gas phase are 2.28, 4.75, 1.69, 3.66, 1.30, 2.94, 1.12, and 2.49 eV, respectively, which agree very well with the available experimental result for H2C3 (2.27 eV). In addition, the vertical excitation energies for both transitions B1B1 ← X1A1 and A1A2 ← X1A1 are found to obey a nonlinear ΔE-n relationship as a function of chain size by performing curves fitting. [ABSTRACT FROM AUTHOR]

In this work, the single and double proton transfer dynamic process in the first excited state of 2,5-bis(2-benzothiazolyl)hydroquinone (BBTHQ) were theoretically investigated based on the time-dependent density functional theory (TD-DFT) method. The calculations of primary bond lengths, bond angles, IR vibrational spectra and NCI analysis reveal that two intramolecular hydrogen bonds of BBTHQ are strengthened in the first excited state, which provides a driving force for excited state proton transfer. The frontier molecular orbitals (FMOs) indicate the nature of intramolecular charge transfer. In addition, the potential energy surfaces (PESs) of the ground state and first excite state were also constructed to further elucidate the mechanism of intramolecular proton transfer of BBTHQ. [ABSTRACT FROM AUTHOR]

Photoelectric conversion efficiency (PCE) is one of the crucial indicators to determine the overall performance of dye-sensitized solar cells (DSSCs), and accurate estimation of PCE is a feasible strategy for developing high-performance DSSC devices. In this contribution, we strategically designed a series of anthracene-based organic dyes 1–4 by introducing different π-bridge or auxiliary acceptor groups. Their photovoltaic properties were explored by first-principles calculations coupled with the normal model and improved normal model. It is found that the introduction of an electron-rich thieno[3,2-b]thiophene-based π-spacer in dye 2 induces a blue-shift of the maximum absorption band with respect to dye 1, while the inclusion of an electron-deficient diketopyrrolopyrrole-based π-bridge in dye 3 and a thieno[3,4-b]pyrazine-based auxiliary acceptor in dye 4 can remarkably extend the optical absorption into the 550–650 nm region. In addition, the open-circuit voltage (VOC), short-circuit photocurrent density (JSC), fill factor (FF) and the corresponding PCE (η) were evaluated by the improved normal model. The estimated results of dye 1 (VOC = 757 mV, JSC = 14.63 mA cm−2, FF = 0.85, and η = 9.41%) reproduce very well the experimentally available data (VOC = 760 mV, JSC = 14.25 mA cm−2, FF = 0.75, and η = 8.08%), suggesting that the improved normal model is an accurate and general method to predict the photoelectric properties of organic dyes. More importantly, dyes 3 and 4 are predicted to exhibit extremely high PCEs of over 32%, both of which are expected to be potential candidates as metal-free organic dyes applied in DSSCs. [ABSTRACT FROM AUTHOR]

Formation of cluster is a popular phenomenon for ionic liquids due to the strong interactions between cation and anion. It would definitely affect the intrinsic properties of ionic liquids and its catalytic activity. Taken the coupling reaction of carbon dioxide and propylene oxide as an example, the effect of quaternary ammonium ionic liquids cluster on its catalytic performance is investigated by combination of ONIOM and molecular dynamics simulations, including quaternary ammonium ionic liquid, hydroxyl functionalized quaternary ammonium ionic liquid, protic quaternary ammonium ionic liquid, and protic hydroxyl functionalized quaternary ammonium ionic liquid. The influence of electrostatic interaction and covalent and non-covalent interactions on the catalytic activity is analyzed by natural bond orbital, electron localization function, and atoms in molecules to explore the critical factors to control the catalytic activity. [ABSTRACT FROM AUTHOR]

Suppressors of cytokine signaling (SOCS) act as negative feedback regulators of the Janus kinase/signal transducer (JAK–STAT) signaling pathway by inhibiting the activity of JAK kinase. The kinase inhibitory region (KIR) of SOCS1 targets the substrate binding groove of JAK with high specificity, as demonstrated by significantly higher IC50 following the mutation of any of residue. To gain a greater understanding of the mechanisms of the inhibition of SOCS1 for JAK1, the binding mode, binding free energy decomposition, and desorption mechanism of JAK–SOCS1 complexes as well as a number of mutant systems were identified by extensive molecular dynamics (MD) simulations and the constant pulling velocity (PCV) method. Electrostatic interactions were identified for their contribution to protein–protein binding, which drove interactions between JAK1 and SOCS1. The polar residues Arg56, Arg59, and Asp105 of SOCS1 and Asp1042 and Asp1040 of JAK1 were key components in the binding, and electrostatic interactions of the side chains were prominent. The binding free energies of the six mutant proteins were lower when compared with those of the control proteins, and the side chain interactions were weakened. The residue Asp1040 played a crucial role in KIR close to the binding groove of JAK1. Moreover, salt bridges contributed significantly to JAK1 and SOCS1 binding and cleavage processes. The study presented herein provides a comprehensive understanding of the thermodynamic and dynamic processes of SOCS1 and JAK1 binding that will contribute meaningfully to the design of future studies related to peptide inhibitors based on SOCS1. [ABSTRACT FROM AUTHOR]

Issue concerning accurate prediction of the reverse intersystem crossing rate (kRISC) is critical for developing novel efficient thermally activated delayed fluorescence (TADF) materials. In this contribution, the kRISC rates from the lowest excited triplet T1 state to the lowest excited singlet S1 state were evaluated for five donor‐π‐acceptor‐type pyrimidine‐based TADF emitters using the semiclassical Marcus theory. Both the singlet‐triplet energy difference (ΔEST) and spin–orbit coupling (V) between the S1 and T1 states were investigated by performing the density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) calculations. In addition, their fluorescence emission wavelengths (λem) were also calculated at the TD‐DFT level. The predicted kRISC and λem values are found to reproduce well the available experimental findings. The present results reveal that the kRISC rates of molecules possessing the unsymmetrical diphenyl pyrimidine acceptor core are calculated to be slightly larger than those of their analogues with the symmetrical diphenyl pyrimidine. In addition, introducing two tert‐butyl groups into the 2,7‐positions of the donor moiety of the latter is also an effective method for increasing kRISC when designing TADF emitters. Such a difference is related to the nature of the T1 excited state. A more remarkable charge‐transfer (CT) contribution to the state can achieve a smaller ΔEST, leading to a more efficient RISC process, and consequently a shorter delayed fluorescence lifetime as observed experimentally. © 2019 Wiley Periodicals, Inc. Five molecules exhibiting the TADF behavior were studied theoretically. Calculations reveal that a remarkable charge‐transfer contribution to the T1 excited state can achieve a smaller singlet‐triplet energy difference. This leads to a more efficient reverse intersystem crossing process. [ABSTRACT FROM AUTHOR]

On the reported TCP‐OH (See Scheme 1), other two star‐shaped molecules are theoretically designed by replacement of side group of TCP‐OH by N,N‐di(4‐methoxyphenyl)aniline for TPAP‐OH and oxygen‐bridged triarylamine for TBOPP‐OH. The core group, phenol, is kept in three molecules. Their potential to be hole transport material in perovskite solar cells without dopants is evaluated by multiscale simulations. The properties of isolated molecules are estimated by the frontier molecular orbital, absorption spectrum, and hole mobility. After that, the HTM@CH3NH3PbI3 adsorbed system is studied to consider the influence of adsorption on HTM performance. Besides the primary judgment, the glass transition temperature is also simulated to determine the stability of amorphous film. Not only the chemical stability is evaluated but also the amorphous film stability is considered. The latter is almost neglected in previous theoretical studies to evaluate the properties of HTMs. The performance of a designed molecule is evaluated from both the isolated molecules and HTM@CH3NH3PbI3 adsorbed system including aforementioned items, which is favorable to build reliable structure‐property relationship. [ABSTRACT FROM AUTHOR]

A reliable quantitative description of photoluminescence efficiency is crucial for designing and developing new-type thermally activated delayed fluorescence (TADF) emitters. In this contribution, we computed the conversion and decay rates of a novel TADF-active molecule, 2-(9H-carbazol-9-yl)-thianthrene-5,5,10,10-tetraoxide (CZ-TTR), involving the lowest singlet excited S1 state and triplet excited T1 state. The efficiency of total fluorescence containing prompt fluorescence and delayed fluorescence was obtained correspondingly. The present results reveal that the rate of reverse intersystem crossing from T1 to S1 is calculated to be slightly larger than the radiative and non-radiative decay rates of the S1 state at 300 K temperature, thus resulting in an occurrence of delayed fluorescence. Additionally, the total fluorescence efficiency is estimated to be 54.5%, which agrees very well with the photoluminescence quantum yield of 56.7% observed experimentally. It is also found that the dominant charge transfer characteristics in the S1 and T1 states produce a small energy difference between the two states, and consequently an efficient reverse intersystem crossing process and a high fluorescence efficiency. [ABSTRACT FROM AUTHOR]

Density functional theory and semi-classical Marcus electron transfer theory were employed to investigate the electron transport properties of a sulfur-containing azaacene molecule 10,14-bis(5-(2-ethylhexyl)thiophen-2-yl)dipyrido[3,2-a:20,30-c][1,2,5]thiadiazolo[3,4-i]phenazine (TDTP), which has been proved to have high performance as an electron transport material in inverted perovskite solar cells in a previous experiment. By changing thiophene rings in both side chains to thiazole/benzene rings, two new compounds TDTP-I and TDTP-II were designed. It has been found that both new compounds have lower HOMO and LUMO energy levels and higher electron mobilities than TDTP. In particular, compound TDTP-II has the highest electron mobility among the three. Furthermore, the adsorption properties of TDTP/TDTP-II adsorbed on perovskite (110) surface systems are also studied. It has been shown that TDTP-II has a more negative adsorption energy than TDTP. So our designed compound TDTP-II is expected to be a potential electron transport material in inverted PSCs and changing the side chains could be a feasible way to improve the electron transport properties. [ABSTRACT FROM AUTHOR]

In this contribution, the photophysical properties of two excited state intramolecular proton transfer (ESIPT) fluorophores of 2,6-dibenzothiazolyl-4-methylphenol (I) and 2-benzothiazolyl-6-(2-(benzothiazolyl)vinyl)-4-methylphenol (II) were studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods at the PBE0 theoretical level. To probe into the origin of the absorption and emission bands observed experimentally, the absorption and emission spectra of I and II were simulated by the TD-PBE0/6-311 + G(d,p) calculations. In addition, the photo-induced proton enol-keto tautomerization of the two targeted molecules was also explored. The present studies indicate that a good agreement is found between theoretical predictions and experimental data. Moreover, both of these molecules can undergo an ultrafast ESIPT process, which should be responsible for the single proton-transfer tautomer emission. [ABSTRACT FROM AUTHOR]

Inverted perovskite solar cells (PSCs) have attracted much attention due to their low-temperature and solution-based process. Electron transport layers are important components in inverted PSCs. Non-fullerene n-type organic small molecules seem to be more attractive as electron transport layers, because their structures are easy to be synthesised and modified. In this paper, density functional theory and semi-classical Marcus electron transfer theory were used to explore the electron transport properties in three azaacene derivatives, including one experimentally reported molecule, 1,4,9,16-tetrakis((triisopropylsilyl)ethynyl)quinoxalino[2‴,3‴:4″,5″]cyclopenta[1″,2″,3″:5′,6′]acenaphtho[1′,2′:5,6]pyrazino[2,3-b]phenazine (1), and two theoretically designed molecules (2 and 3). Compound 2 is formed by substituting i-Pr groups in compound 1 with H atoms, which is designed to evaluate the effect of i-Pr groups on the electron transport properties. Compound 3 is designed by adding one more benzopyrazine group to the conjugation structure of compound 1. It shows that i-Pr group can increase HOMO and LUMO energy levels and improve solubility in organic solvent and hydrophobicity. Enlarging conjugation can not only decrease LUMO energy level and electron reorganisation energy, but also can increase solubility and electron mobility. So our designed compound 3 is expected to be a potential electron transport material in inverted PSCs. [ABSTRACT FROM AUTHOR]

According to one experimentally reported thermally activated delayed fluorescence (TADF) emitter (AcDPA‐2TP), two new molecules (AcDPA‐2PP and AcDPA‐TPP) have been designed theoretically to probe into the effect of different acceptor strengths on their TADF mechanisms. In this work, the rates of reverse intersystem crossing (kRISC) of the three targeted molecules were calculated by the semiclassical Marcus rate expression. The present results demonstrate that the kRISC rate of AcDPA‐2PP is estimated to be 5.56 × 106 s−1, about twice larger than that of AcDPA‐2TP (2.63 × 106 s−1), and especially AcDPA‐TPP is found to exhibit the largest kRISC value (6.97 × 106 s−1) among the three molecules. Considering that AcDPA‐2TP has been observed to be an efficient TADF emitter, our newly designed two molecules AcDPA‐2PP and AcDPA‐TPP are also expected to be potential TADF materials. © 2018 Wiley Periodicals, Inc. Three thermally activated delayed fluorescence (TADF) emitters were studied theoretically, where AcDPA‐2TP is an experimentally reported molecule, and AcDPA‐2PP and AcDPA‐TPP are two theoretically designed molecules. Calculations reveal that the reverse intersystem crossing rates follow the order of AcDPA‐TPP > AcDPA‐2PP > AcDPA‐2TP. Considering that AcDPA‐2TP has been observed to be an efficient TADF emitter, AcDPA‐2PP and AcDPA‐TPP are also expected to be potential TADF materials. [ABSTRACT FROM AUTHOR]

Discotic liquid crystal (DLC) materials have attracted considerable attention mainly due to their high charge carrier mobilities in quasi‐one‐dimensional columns. In this article, five hexaazatrinaphthylene‐based DLC molecules were investigated theoretically, and their frontier molecular orbital energy levels, crystal structures, and electron/hole drift mobilities were calculated by combination of density functional theory (DFT) and semiclassical Marcus charge transfer theory. The systems studied in this work include three experimentally reported molecules (1, 2, and 3) and two theoretically designed molecules (4 and 5). Compared with the 1–3 compounds, 4 and 5 have three more extended benzene rings in the π‐conjugated core. The present results show that the orders of the frontier molecular orbital energy levels and electron drift mobilities agree very well with the experiment. For 4 and 5, the electron/hole reorganization energies are lower than those of compounds 1–3. Furthermore, the calculated electron/hole transfer integral of 5 is the largest among all the five systems, leading to the highest electron and hole mobilities. In addition, the hydrophobicity and solubility were also evaluated by DFT, indicating that compound 5 has good hydrophobicity and good solubility in trichloromethane. As a result, it is expected that compound 5 can be a potential charge transport material in electronic and optoelectronic devices. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The viscosity is one of the most important properties of ionic liquids (ILs). To uncover the relationship between structure and viscosity from the molecular level is beneficial to designing the ILs with desired viscosity by choice of different cation and anion. The influence of hydrogen bonds on the viscosity for five pyridine-based ILs, [EPy][OTf], [EPy][NTf], [BPy][OTf], [BPy][NTf], and [BPy][BF], is theoretically studied by combination of molecular dynamics and quantum chemistry. Effect of different alkyl chain lengths, cations, and anions on the viscosity is compared to find the critical item. Besides the molecular structure, the roles of hydrogen bond played in the viscosity are analyzed by various factors. [ABSTRACT FROM AUTHOR]

Excited-state intramolecular proton transfer (ESIPT) reactions of three amino-type 2-(2'-aminophenyl)benzothiazole (PBT-NH2) derivatives, that is, 2-(2'-methylaminophenyl)benzothiazole (PBT-NHMe), 2-(2'-acetylaminophenyl)benzothiazole (PBT-NHAc) and 2-(2'-tosylaminophenyl)benzothiazole (PBT-NHTs), have been explored by the time-dependent density functional theory (TD-DFT) method with the B3LYP density functional. In addition, their absorption and fluorescence spectra were also simulated at the same theoretical level. The present studies reveal that the energy barriers of the first singlet excited state of the three titled compounds along the ESIPT reactions are predicted at 0.39, 0.30 and 0.12 eV, respectively, suggesting that the inclusion of a strong electron-withdrawing tosyl group can remarkably facilitate the occurrence of the ESIPT reaction, while the involvement of an electron-donating methyl group has no effect on the ESIPT process of the amino-type hydrogen-bonding system. Following the ESIPT, both PBT-NHAc and PBT-NHTs molecules can also undergo thecis–transisomerisation reactions along the C2–C3bond between benzothiazole and phenyl moieties, in which the energy barriers of thetrans-tautomer →cis-tautomer isomerisations in both ground states are calculated at 0.33 and 0.27 eV, respectively. This implies that there may exist a long-livedtrans-tautomer species in the ground states for PBT-NHAc and PBT-NHTs, as observed in the spectroscopic experiments of PBT-NHTs. [ABSTRACT FROM AUTHOR]

1,8-Dihydroxydibenzo[a,h]phenazine (DHBP) is a new synthetic compound possessing two intramolecular hydrogen bonds; however, it has been found to exhibit the excited-state intramolecular single proton transfer (ESSPT) behaviour, in recent experiment. To explain the phenomenon reasonably, two combined methods of CASSCF/CASPT2 and DFT/TD-DFT have been employed to investigate the structural and spectral properties of its three tautomers, corresponding to the non-proton-transferred (E), the single-proton-transferred (SK) and the double-proton-transferred (DK) forms. These studies suggest that the E form is the global minimum in the S0state, while the SK form is the most stable in the S1state, both of which are responsible for the experimental absorption peak at 2.54 eV and emission band at 1.64 eV, respectively. Because of the relatively high energy barrier, the DK form will play no important role in the fluorescence emission of DHBP. The present results lend a good support to the experimental finding of single proton transfer (SPT). [ABSTRACT FROM AUTHOR]

In this work, the low-lying electronic singlet states of 9-methylhypoxanthine (9MHPX) were explored by the complete active space self-consistent-field (CASSCF) and complete active space second-order perturbation theory (CASPT2) calculations, and the conical intersections between the optically bright excited S1state and ground S0state were optimised by the two-root state-averaged SA-2-CASSCF approach. These studies indicate that four slightly different kinds of S1/S0conical intersections are identified computationally for 9MHPX, corresponding to four main internal conversion pathways, respectively, all of which are found to show the comparable timescales according to dynamics simulations. At the CASPT2 level, four brightππ* transitions of 9MHPX are calculated to locate at 4.47, 5.35, 5.97 and 6.30 eV, respectively, responsible for the available experimental absorption peaks of 9MHPX in the vapour phase (4.41, 5.19, 6.05 and 6.42 eV). Though one relatively weakππ* transition computed at 5.69 eV is not observed in the vapour phase, it is in accordance with the circular dichroism measurement of another hypoxanthine derivative deoxyinosine 5'-phosphate near 5.51 eV. [ABSTRACT FROM PUBLISHER]

The mechanism of reaction HCNO + HO2 is investigated by means of CCSD(T)/6-311 + G(d,p)//B3LYP/6-311 + G(d,p) method, in which Pi with the i = 1, 2, 3, ..., 7 are involved, to determine a more reasonable pathway. Among four possible entrance patterns, the attack of oxygen to carbon is the most energetically feasible leading to complex a1. Starting from the a1, the rupture of O2–O3 bond to form P3 (HC(O)NO + OH) is the most favorable pathway. Alternatively, the a1 undergoes N–O1 bond rotation to form the isomer a2. A concerted O2–O3 bond and C–N bond cleavage leading to P4 (OH + HCO + NO) is the secondary feasible pathway. Other products are not energetically accessible because of higher barrier-consumed and/or complicated processes. We hope that the present work would be helpful to experimentally identify the product distributions and deeply understand the mechanism of the title reaction. [ABSTRACT FROM AUTHOR]

The photoinduced reaction mechanism of excited-state intramolecular proton transfer (ESIPT) of 1,8-dihydroxydibenzo[a,c]phenazine (denoted as DHBP), a bis-phenol displaying ESIPT property, has been explored by employing the CASSCF/CASPT2 and DFT/TD-DFT methods. The two lowest singlet electronic states of three tautomers, namely the enol form (E), a keto form with single proton transferred (SK) and a keto form with double proton transferred (DK), have been optimized. These results indicate that the E tautomer is the system with the lowest energy in the ground S0 state, while the SK tautomer is the most stable structure in the singlet S1 state. Moreover, the structural changes of E from S0 to S1 result in a strengthened intramolecular hydrogen bond, which contributes to facilitate the following ESIPT reaction. In addition, the absorption and emission spectra of DHBP have also been simulated using TD-DFT. The vertical excitation energy of the E form and vertical emission energy of the SK form are found at 2.86 and 1.74 eV, respectively, in good agreement with the available experimental values of 2.89 and 1.72 eV, which implies that the fluorescence detected by Piechowska et al. may only arise from the SK tautomer. To give a clearer picture of the proton transfer process, the constrained energy profiles (CEPs) for the three DHBP tautomers in the S0 and S1 states have been constructed. These calculations of CEPs show that the energy barriers during the PT processes from the E/DK to the SK forms in the S1 state are much lower than those of the others considered here and support the hypothesis of an ESIPT mechanism of only a singlet proton transfer rather than double proton transfer. [ABSTRACT FROM AUTHOR]

The electronic structures and photophysical properties of three homoleptic iridium(iii) complexes IrL3 with C^N ligands, including 2a (L = 1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole), 5a (L = 1-(2,6-dimethylphenyl)-2-phenyl-1H-imidazole), and 6a (L = 1-(3,5-diisopropylbiphenyl-4-yl)-2-phenyl-1H-imidazole), are investigated by means of the density functional method. Furthermore, seven new complexes are theoretically designed, including 1a (L = 1,2-diphenyl-1H-imidazole), 3a (L = 1-(2,6-dimethoxyphenyl)-2-phenyl-1H-imidazol), 4a (L = 2-(2-phenyl-1H-imidazol-1-yl)isophthalaldehyde), 1b (L = 2-(biphenyl-3-yl)-1H-imidazole), 2b (L = 2-(2′,6′-diisopropylbiphenyl-3-yl)-1H-imidazole), 3b (L = 2-(2′,6′-dimethoxybiphenyl-3-yl)-1H-imidazole), and 4b (L = 3′-(1H-imidazol-2-yl)biphenyl-2,6-dicarbaldehyde), to explore the influence of different substituents and different substituted positions on the electronic structures, phosphorescence properties, and organic light-emitting diode (OLED) performance. The HOMO–LUMO energy gap is greatly decreased by introduction of the –CHO group into the phenyl ring (4a and 4b see SCHEMREFScheme 1/SCHEMREF―sketched structures for all the investigated Ir(iii) complexes). As a result, their absorption and emission spectra present red-shifting leading them to be potential red-emitting phosphors. Other complexes are all blue-emitting materials, indicating that the effect of the substituted position on the emitting color is negligible. However, the addition of the substituent on the para-position of the phenyl ring in the phenylimidazole ligand would increase the quantum yield and electroluminescence (EL) performance compared with that on the imidazole ring. [ABSTRACT FROM AUTHOR]

Chlorine-containing organic compounds have been of major interest since such compounds would serve as temporary reservoirs for HO X, RO X and ClO X radicals. Moreover, it would transport chlorine species to the atmosphere and stratosphere. However, limited studies have been performed on the 2-chlorinated ethyl hydroperoxide. In this work, the mechanism of unimolecular dissociation of 2-chlorinated ethyl hydroperoxide is theoretically studied. The equilibrium structures are optimized at the Boese-Martin for kinetics (BMK) level. And the energies are further refined at the Balanced multi-coefficient correlation-coupled cluster theory with single and double excitations (BMC-CCSD) level on the basis of the optimized geometries. Fifteen reaction channels are finally confirmed including the direct C-O, O-O, O-H, and C-C bond cleavage or the H2-, H2O-, H2O2-, and CH3Cl-elimination. The mechanism of unimolecular dissociation of 2-chlorinated ethyl hydroperoxide is studied by BMC-CCSD//BMK method. Fifteen pathways are determined. The direct O-O bond cleavage is one of the dominant reaction channels. [ABSTRACT FROM AUTHOR]

Excited-state intramolecular proton transfer (ESIPT) of four imidazole derivatives, 2-(2'-hydroxyphenyl)imidazole (HPI), 2-(2'-hydroxyphenyl)benzimidazole (HPBI), 2-(2'-hydroxyphenyl)-1Hphenanthro[9,10-d]imidazole (HPPI) and 2-(2'-hydroxyphenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (HPPPI), were studied by the sophisticated CASSCF/CASPT2 methodology. The stateaveraged SA-CASSCF method was used to optimize their geometry structures of S0 and S1 electronic states, and the CASPT2 calculations were used for the calibration of all the single-point energies, including the absorption and emission spectra. A reasonable agreement is found between the theoretical predictions and the available experimental spectral data. The forward ESIPT barriers of four target compounds gradually decrease with the increase of molecular size. On the basis of the present calculations, it is a plausible speculation that the larger the size, the faster is the ESIPT rate, and eventually, HPPPI molecule can undergo a completely barrierless ESIPT to the more stable S1 keto form. Additionally, taking HPI as a representative example, the radiationless decays connecting the S0 and S1/S0 conical intersection structures were also studied by constructing a linearly interpolated internal coordinate (LIIC) reaction path. The qualitative analysis shows that the LIIC barrier of HPI in the keto form is remarkably lower than that of its enol-form, indicating that the former has a big advantage over the latter in the nonradiative process. [ABSTRACT FROM AUTHOR]

The fixation of carbon dioxide with epoxide catalysed by a series of carboxylic acidic functionalised ionic liquids (ILs) catalysts is investigated by density functional theory method. Except for the catalysts reported by the experiment, the catalytic activity of a new designed catalyst (4c see Scheme 1) is also explored. These ILs are categorised into four groups according to the different cation structures and number of functional groups. The effects of different chain length, anion, and cation structure on the catalytic activity are explored. The elongation of alkyl chain length in cation will increase the product yield, while increasing the chain bulk has almost negligible effect on the enhancement of catalytic activity. Utilisation of imidazole group as the cation is better than pyridine group. And the cation with two functional groups will have a better catalytic activity than that with one functional group. [ABSTRACT FROM PUBLISHER]

The methyl-transfer mechanism of humanN-acetylserotonin methyltransferase and the roles of several residues around the active sites are investigated by density function theory method. This enzyme will catalyse the conversion ofN-acetylserotonin and S-adenosyl-L-methionine (SAM) into melatonin and S-asenosylhomocysteine, which is the terminal step in the melatonin (N-acetyl-5-methoxytryptamine) biosynthesis. The calculated results confirm that the methyl transfer and proton transfer will take place via aSN2 step with a concerted mechanism, which is different from the experimental estimation via a water bridge. The residues H255, D256, E311, and R252 play an important role in reducing the barrier height and inducing methyl transfer. In addition, a full SAM molecule is considered in this work, which is never explored in previous reports. We find that some residues around the SAM in the centre of active site are essential factors to influence the mechanism and barrier height. So a truncated SAM model may not be suitable for all reactions. [ABSTRACT FROM PUBLISHER]

Various catalysts have been explored for the coupling reaction of carbon dioxide with propylene oxide in the past decade. However, the search for high-efficiency single-component catalyst in the absence of metal and solvent is still a challenging issue. In this work, the catalytic activity of a series of functionalized phosphonium-based ionic liquids (FPBILs) is investigated by density functional theory. The influences of functional group, chain length of cation, and anion on the catalytic performance have been explored. The carboxyl-functionalized FPBIL with the moderate alkyl chain length presents the best catalytic activity among all investigated catalysts. On the basis of above information, a new sulfonyl hydroxide-functionalized FPBIL is designed. Moreover, its catalytic activity is theoretically examined as compared with that of carboxyl-functionalized FPBIL. [ABSTRACT FROM AUTHOR]

The geometric and electronic structures, phosphorescence properties and the organic light-emitting diode (OLED) performance of a series of Ir(iii) complexes based on bis[(4,6-di-fluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) were investigated by using density functional theory/time-dependent density functional theory (DFT/TD-DFT), including Ir(iii)bis[2-(2,4-difluorophenyl)-4-(tert-butyl)pyridinato-N,C2′]picolinate (1a), Ir(iii)bis[2-(2,4-difluorophenyl)-4-(n-heptyl)pyridinato-N,C2′]picolinate (2a), Ir(iii)bis[2-(2,4-difluorophenyl)-4-(3-ethylheptyl)pyridinato-N,C2′]picolinate (3a), Ir(iii)bis[2-(2,4-difluorophenyl)-4-(2,4,6-trimethylphenyl)pyridinato-N,C2′]picolinate (5a), and Ir(iii)bis[2-(2,4-difluoro-3-(2,4,6-trimethylphenyl)phenyl)-pyridinato-N,C2′] picolinate (5b). To explore the influence of the substituted positions on the optical and electronic properties of the Ir(iii) complexes, seven other new complexes were designed by introducing the substituted groups on the difluorophenyl rings or pyridine rings. After introducing the phenyl substituted groups on the pyridine or difluorophenyl rings of cyclometalated ligands, the HOMO–LUMO energy gap is decreased. Thus, the absorption spectra of 4a and 4b undergo a red-shifting, especially for 4a, and have a stronger absorption strength that will be beneficial to improving their quantum yields, which is proved by the further evaluation of the radiative (kr) and non-radiative (knr) rate constants. The combinations of a larger 3MLCT-3MC energy gap, smaller ΔES1–T1, and higher contribution of 3MLCT in the emission process result in the higher quantum yields for complexes 4a and 4b. Besides, the designed complexes 4a and 4b are considered to be potential candidates as blue-emitting materials with better equilibrium between the hole transport (λhole) and electron transport (λelectron). [ABSTRACT FROM AUTHOR]

Binding properties of wild type (WT) and six single amino acid substituted variants (E3A, E9A, D12A, D20A, F23A, and E58A) of insulin-like growth factor I (IGF-I) were analyzed with respect to their binding details to IGF binding proteins (IGFBPs) by molecular dynamics (MD) simulations. The binding sites and binding interactions on IGF-I and IGFBPs are screened and compared with the static X-ray structure. Electrostatic interaction is the primary driving force of the interaction between IGF-I and IGFBPs. Mutation may cause the rearrangement of binding sites, however, the unfolding of protein induced by mutation is not obvious in this work. We also provide the detailed picture of binding factors. And the results show that, whether the unfolding of helix occurs or not, the Ala mutation will change the molecular atmosphere of the binding interface by the rearrangement of conformation, and further affects the binding residues and binding interactions. [ABSTRACT FROM AUTHOR]

The mechanisms of hydrogen release from methylamine with or without borane, alane, diborane, dialane, and borane–alane are theoretically explored. Geometries of stationary points are optimised at the MP2/aug-cc-pVDZ level and energy profiles are refined at the CCSD(T)/aug-cc-pVTZ level based on the second-order Møller–Plesset (MP2) optimised geometries. H2elimination is impossible from the unimolecular CH3NH2because of a high energy barrier. The results show that all catalysts can facilitate H2loss from CH3NH2. However, borane or alane has no real catalytic effect because the H2release is not preferred as compared with the B–N or Al–N bond cleavage once a corresponding adduct is formed. The diborane, dialane, and borane–alane will lead to a substantial reduction of energy barrier as a bifunctional catalyst. The similar and distinct points among various catalysts are compared. Hydrogen bond and six-membered ring formation are two crucial factors to decrease the energy barriers. [ABSTRACT FROM AUTHOR]

The reaction mechanisms of methylhydrazine (CH3NHNH2) with O(3P) and O(1D) atoms have been explored theoretically at the MPW1K/6-311+G(d,p), MP2/6-311+G(d,p), MCG3-MPWPW91 (single-point), and CCSD(T)/cc-pVTZ (single-point) levels. The triplet potential energy surface for the reaction of CH3NHNH2with O(3P) includes seven stable isomers and eight transition states. When the O(3P) atom approaches CH3NHNH2, the heavy atoms, namely N and C atoms, are the favourable combining points. O(3P) atom attacking the middle-N atom in CH3NHNH2results in the formation of an energy-rich isomer (CH3NHONH2) followed by migration of O(3P) atom from middle-N atom to middle-H atom leading to the product P6 (CH3NNH2+OH), which is one of the most favourable routes. The estimated major product CH3NNH2is consistent with the experimental measurements. Reaction of O(1D) + CH3NHNH2presents different features as compared with O(3P) + CH3NHNH2. O(1D) atom will first insert into C–H2, N1–H4, and N2–H5 bonds barrierlessly to form the three adducts, respectively. There are two most favourable paths for O(1D) + CH3NHNH2. One is that the C–N bond cleavage accompanied by a concerted H shift from O atom to N atom (mid-N) leads to the product PI(CH2O + NH2NH2), and the other is that the N–N bond rupture along with a concerted H shift from O to N (end-N) forms PIV(CH3NH2+ HNO). The similarities and discrepancies between two reactions are discussed. [ABSTRACT FROM AUTHOR]