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The effects of different donors, acceptors, and electron bridges on various properties of novel organic electro-optic materials are investigated. We synthesized and systematically researched 12 chromophores with different donors including alkylaniline, bis(4-piperidinyl)phenyl, bis(N,N-diethyl)aniline, and julolidine derivatives and acceptors including tricyanofuran (TCF) or phenyl-trifluoromethyl-tricyanofuran (3F-TCF) and pentafluorobenzene-tricyanofuran (5F-TCF) linked together via isophorone derivatives as the bridges. We tested the thermodynamic characteristics, photophysical properties, DFT theoretical calculations, and electro-optical properties of 12 chromophores to summarize the relationship between the chromophore structure and performance. The results indicate that not the strongest donor pairs with the strongest acceptors exhibit the best performance, for example, chromophores C5 and D5 with strong bis(N,N-diethyl)aniline and julolidine donors exhibit the highest electro-optic coefficients (245 and 228 pm V−1), while they only modify with relatively weaker 5F-TCF acceptors. For weak alkylaniline, bis(4-piperidinyl)phenyl donors, the 3F-TCF acceptor can achieve the maximum electro-optic coefficient (151 and 189 pm V−1). [ABSTRACT FROM AUTHOR]

We present a combined computational and experimental study of CO2 activation at the Sc2O2+ metal oxide ion center in the gas phase. Density functional theory calculations on the structures of [Sc2O2(CO2)n]+ (n = 1–4) ion–molecule complexes reveal a typical end-on binding motif as well as bidentate and tridentate carbonate-containing configurations. As the number of attached CO2 molecules increases, activated forms tend to dominate the isomeric populations. Distortion energies are unveiled to account for the conversion barriers from molecularly bound isomers to carbonate structures, and show a monotonically decreasing trend with successive CO2 ligand addition. The infrared photodissociation spectra of target ion–molecule complexes were recorded in the 2100–2500 cm−1 frequency region and interpreted by comparison with simulated IR spectra of low-lying isomers representing distinct configurations, demonstrating a high possibility of carbonate structure formation in current experiments. [ABSTRACT FROM AUTHOR]

Coincidental realization of broadband spectral coverage and high resolution in one spectrometer system has always been a challenge. Here, we report the development of a high-resolution visible CCD spectrometer based on the virtually imaged phase array (VIPA) technique. By using a thin glass plate and a reflective grating, a two-dimensional cross-dispersion was realized. A broadband coverage of ∼14.94 THz and a high resolution of ∼1 GHz at 632.996 nm were achieved with a simple structure. The effects of the surface quality of VIPA etalon, the pixel size of the CCD camera, the pinhole size of the input beam, and the focal length of the imaging lens on the resolution of the spectrometer and the transverse spot size on the detector plane were considered. A comparison between the experimental results by changing the imaging lens and the theoretical calculation results proved a better simulation of these two parameters, which is a helpful contribution to the design and construction of a VIPA spectrometer. The developed spectrometer will provide a useful tool for the study of high-resolution spectroscopy and for simultaneous multi-species trace detection. [ABSTRACT FROM AUTHOR]

ZIF-8-derived single atom catalysts (SACs) have been widely reported and show prospects for various electrocatalytic reactions. In addition to the coordination environments of the single atoms, the geometric shape and morphology of ZIF-8 also affect the catalytic performances, which is somewhat unnoticed and not studied thoroughly at the current stage. Herein, we report a polyelectrolyte brush-templated-growth approach to synthesize ZIF-8-derived SACs with different hollow carbon nanoarchitectures. An anionic spherical poly(acrylic acid) brush (PAA-SPB) with a highly negatively charged polyelectrolyte brush layer is rationally designed and used to grow ZIF-8 nanocrystals in situ via a spatial confinement strategy. Such an approach is verified for the synthesis of Fe, Co, Cu, and Pd single-atom catalysts, respectively. In particular, the as-synthesized Fe single-atom catalysts are used to highlight the advantages of this synthetic approach, realizing superior oxygen reduction reaction (ORR) performance and outperforming the benchmark Pt/C. The morphology and structure of a ZIF-8-derived carbon matrix based on PAA-SPB and its effect on the ORR performance are studied intensively. It is revealed that more Fe single atom active sites are exposed, while the mass transfer in the electrochemical process is promoted via the elaborate tuning of carbon architectures. This work provides a new synthetic strategy that is facile, controllable, and general for achieving the delicate design of the high-performance single-atom catalysts from the aspect of the supports. [ABSTRACT FROM AUTHOR]

The cross-reaction of ethyl peroxy radicals (C2H5O2) with methyl peroxy radicals (CH3O2) (R1) has been studied using laser photolysis coupled to time resolved detection of the two different peroxy radicals by continuous wave cavity ring down spectroscopy (cw-CRDS) in their AÖX~; electronic transition in the near-infrared region, C2H5O2 at 7602.25 cm−1, and CH3O2 at 7488.13 cm−1. This detection scheme is not completely selective for both radicals, but it is demonstrated that it has great advantages compared to the widely used, but unselective UV absorption spectroscopy. Peroxy radicals were generated from the reaction of Cl-atoms with the appropriate hydrocarbon (CH4 and C2H6) in the presence of O2, whereby Cl-atoms were generated by 351 nm photolysis of Cl2. For different reasons detailed in the manuscript, all experiments were carried out under excess of C2H5O2 over CH3O2. The experimental results were best reproduced by an appropriate chemical model with a rate constant for the cross-reaction of k = (3.8 ± 1.0) × 10−13 cm3 s−1 and a yield for the radical channel, leading to CH3O and C2H5O, of (φ1a = 0.40 ± 0.20). [ABSTRACT FROM AUTHOR]

The Cl-initiated oxidation of methacrolein (MACR, C4H6O) under NOx-free conditions has been investigated in a fast flow tube by using a home-made vacuum ultraviolet (VUV) photoionization mass spectrometer complemented by high-level theoretical calculations. The key species such as intermediates and radicals together with products involved in the oxidation are observed online and confirmed in photoionization mass spectra. The reaction potential energy surfaces of the transient C4H5O and C4H6OCl radicals, formed from the hydrogen-abstraction reaction and the addition reaction of MACR with Cl atoms, with oxygen have been theoretically calculated to illuminate the formation of the peroxy radicals of C4H5OO2 and C4H6OClO2. The photoionization processes of these peroxy radicals, whose cations are not stable, and their individual self-reactions as well as bimolecular reactions with HO2 radical are studied and discussed. In addition, kinetic experiments are also performed to get the time evolution of specific products and compared with theoretical models, providing a detailed insight into the reaction mechanism of the Cl-initiated oxidation of MACR. [ABSTRACT FROM AUTHOR]

We present a vacuum ultraviolet (VUV) photoionization study of the gas-phase sulfuric acid (H2SO4) molecule in the 11–14 eV energy range by using the method of synchrotron radiation-based double imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy complemented with accurate theoretical calculations. The slow photoelectron spectrum (SPES) of H2SO4 has been acquired and the three electronic states of H2SO4+, X2A, A2A and B2A have been populated and assigned. The adiabatic ionization energy of the H2SO4 molecule towards the X2A cationic ground state is measured at 11.684 ± 0.006 eV, in accordance with high-level calculated findings. With increasing photon energies, the H2SO4+ cation dissociates into HSO3+ and OH fragments and their adiabatic appearance energy is measured at 13.498 ± 0.007 eV. Then, the enthalpies of formation for the species involved in the photoionization and dissociative photoionization have been determined through a thermochemical cycle. [ABSTRACT FROM AUTHOR]

We study the conformers of the ethyl peroxy radical (C2H5O2), the simplest peroxy radical having more than one conformer, by combining synchrotron radiation vacuum ultraviolet (VUV) photoionization mass spectrometry with theoretical calculations. The ethyl peroxy radical is formed in a microwave discharge flow tube through the reaction of the ethyl radical (C2H5) with oxygen molecules, where C2H5 is generated via the hydrogen-abstraction reaction of ethane with fluorine atoms. Two kinds of C2H5+, originating from photoionization of C2H5 and from dissociative photoionization of C2H5O2, whose cation is not stable, have been identified and separated in photoionization mass spectra. The photoionization spectrum corresponding to C2H5O2 is obtained and assigned with Franck–Condon calculations. The present findings show that the gauche conformer (G-C2H5O2) of C2H5O2 has favorable Franck–Condon factors in the ionization transitions, whereas the contribution of the trans conformer (T-C2H5O2) to the photoionization spectrum is minor or negligible due to its large geometric changes in the photoionization process. Moreover, the reason for the instability of C2H5O2+ and its detailed dissociation mechanisms have been unraveled with the aid of the calculated potential energy curves. [ABSTRACT FROM AUTHOR]

The two isomers of the propylperoxy radical 1-C3H7O2 and 2-C3H7O2, together with their individual rotamers, are identified and assigned by threshold photoelectron spectroscopy with the aid of high-level theoretical computations, from which their accurate adiabatic ionization energies are derived. This study paves the way to probing elusive peroxy radicals and their isomers in advanced mass spectrometry analysis of combustion and atmospheric reactions. [ABSTRACT FROM AUTHOR]

Four nonlinear optical chromophores A–D based on the thiolated-isophorone-derived bridge have been synthesized and systematically investigated. In particular, both the donor and bridge sections of the chromophores were functionalized with different isolation groups including tert-butyltrimethylsilane, tert-butyl(methyl)diphenylsilane, benzene ring and 1,2,3,4,5-pentafluorobenzene ring, respectively. All these four chromophores showed high thermal stabilities with decomposition temperatures above 220 °C. Most importantly, the rigid steric hindrance groups can effectively reduce the intermolecular electrostatic interactions to transform their hyperpolarizabilities into large electro-optic (EO) coefficients (r33). Polymeric thin films doped with 30 wt% chromophores A–D have been poled to afford large r33 values of 96, 143, 115, and 109 pm V−1 at 1.31 μm, respectively. Electro-optic performance together with density functional theory (DFT) calculations suggests that the isolation groups show different effects on the hyperpolarizability and poling efficiency of chromophores. The normalized r33 value of chromophore B increased to 8.36 × 10−19 pm cc per (V molecules) indicating the largest steric hindrance group and the highest polarization efficiency. All these results provide valuable insight into the understanding of the impact of isolation groups on macroscopic EO activities of materials. [ABSTRACT FROM AUTHOR]

The preparation of scaffolds represents a huge challenge for meniscus tissue engineering, as there are particular biomechanical and biodegradability requirements. Here, an amphiphilic polymer was prepared by grafting hydrophobic poly(ε-caprolactone) (PCL) with short chains onto hydrophilic biodegradable poly(l-glutamic acid) (PLGA). PLGA-g-PCL was then crosslinked with triethylene glycol (TEG) to form a chemically crosslinked network (CCN), followed by the in situ formation of stable hydrophobic PCL clusters inside the preformed CCN to increase the strength and elasticity of the hydrogel. The spindle-like PCL clusters in the hydrogel were observed to possess a mean size of 5–10 μm on the long axis and 3–4 μm on the minor axis, with no crystallization according to WAXS. Owing to the hydrophobic association of PCL, the swollen CCN was secondarily crosslinked and stiffened. Dynamic mechanical analysis (DMA) demonstrated excellent rebound resilience, and the maximum compressive strength of all the PLGA-g-PCL hydrogels was greater than 0.60 MPa with a maximum strain of about 70%, which represented significant increases in comparison with a PLGA hydrogel. Owing to the short chains of PCL, degradation of the PLGA-g-PCL hydrogel was accelerated within 3 months in vivo. A hydrogel carrying adipose-derived stem cells (ASCs) effectively regenerated meniscus-like tissue in vivo and preserved the corresponding articular cartilage from degeneration over a 16 week period. [ABSTRACT FROM AUTHOR]

A hydrogel with excellent mechanical properties and self-healing ability provides a promising tool for the repair of load-bearing tissues under a dynamic microenvironment. In this study, poly(l-glutamic acid) (PLGA)-based composite hydrogels with good toughness and self-healing ability were fabricated via filling soft self-healing hydrogels into a tough porous hydrogel skeleton. The PLGA-based tough porous hydrogel skeleton was treated by laser ablation to form a uniform porous structure with 85% porosity and 260 μm pore diameter, and the structure formation was reinforced by the hydrophobic assembly mechanism. The resulting hydrogel skeleton possessed good toughness (maximum compressive stress of 0.51 MPa with strain of 80%) and could fully recover after cyclic compression tests. Furthermore, PLGA-based self-healing hydrogels were fabricated based on a Schiff base reaction, followed by being composited with a tough porous hydrogel skeleton. More importantly, the composite hydrogel exhibited a homogenous interpenetrated structure that inherited mechanical strength and the self-healing ability of the two original compositions. These composite hydrogels exhibited a compressive failure stress of 0.21 MPa at a 63% strain, which was 1.3-fold higher than the value of the original porous hydrogel skeleton at 63% strain. The healing percentage gradually reached 81% within 6 h, indicating the good self-healing efficiency. Furthermore, live/dead staining images revealed that 89% of laden cells remained alive after culture for 7 days. Moreover, the composite hydrogel could self-heal even after cell encapsulation. The developed PLGA-based composite hydrogel will be a promising biomaterial for the repair of load-bearing tissues. [ABSTRACT FROM AUTHOR]

In this study, a mesoporous biocarbon material (BCM) with connected pore channels and a large specific surface area (525.83 m2 g−1) was prepared by a carbonization approach with inexpensive hemp stem as the raw material. The BCM was used as a template to fabricate porous nickel–cobalt oxide (Ni–Co-O) nanocomposite structures in situ. The composition of the Ni–Co-O nanocomposites was readily controlled by adjusting the Co-to-Ni ratio of the initial nickel and cobalt nitrates. Furthermore, we constructed porous Ni–Co-O nanocomposite-based sensors. The room-temperature (RT) NH3 sensing results indicated that the sensor with the best performance exhibited a high response of 3 to 100 ppm, a low detection limit of 50 ppb, good stability (higher than 7 weeks), and excellent reversibility and selectivity. Therefore, the Ni–Co-O nanocomposite, featuring a large specific surface area and meso/micropore distributions, is a strong candidate as a key material for the fabrication of RT NH3 detection sensors. [ABSTRACT FROM AUTHOR]

The PERCA (PEroxy Radical Chemical Amplification) technique, which is based on the catalytic conversion of ambient peroxy radicals (HO2 and RO2, where R stands for any organic chain) to a larger amount of nitrogen dioxide (NO2) amplified by chain reactions by adding high concentrations of NO and CO in the flow reactor, has been widely used for total peroxy radical RO2* (RO2* = HO2 + ΣRO2) measurements. High-sensitivity and accurate measurement of the NO2 concentration plays a key role in accurate measurement of the RO2* concentration. In this paper, we report on the development of a dual-channel chemical amplification instrument, which combined the PERCA method with the incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), for peroxy radical measurements. The IBBCEAS method is capable of simultaneously measuring multiple species with high spectral identification, and can directly measure NO2 concentrations with high sensitivity and high accuracy and without interference from other absorbers. The detection sensitivity of the developed PERCA–IBBCEAS instrument for HO2 radicals was estimated to be about 0.9 pptv (1σ, 60 s) at a relative humidity (RH) of 10%. Considering the error sources of NO2 detection, CL determination, and the radical partitioning in the air sample, the total uncertainty of RO2* measurements was about 16–20%. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet (VUV) photoionization and dissociative photoionization of CH3Cl in the energy range of 11–17 eV have been investigated in detail by combining synchrotron radiation and double imaging photoelectron photoion coincidences (i2PEPICO). Three low-lying electronic states of the CH3Cl+ molecular ion, X2E, A2A1 and B2E, were prepared and analyzed. The appearance energies of the energetically accessible fragment ions, CH2Cl+, CHCl+, CH3+ and CH2+, have been obtained from their respective mass-selected threshold photoelectron spectra (TPES) or photoionization efficiency (PIE) curves. The dissociation mechanisms of energy-selected CH3Cl+ ions, prepared in the A2A1 and the B2E electronic states, as well as outside the Franck–Condon region, have been revealed to be state-specific via ion/electron kinetic energy correlation diagrams. In particular, the umbrella mode vibrational progression of the CH3+ fragment ion in the direct dissociation of the A2A1 electronic state was identified and assigned indicating that this state correlates to the CH3+(11A1′) + Cl(2P1/2) dissociation limit, in agreement with the theoretical calculations performed in this work. [ABSTRACT FROM AUTHOR]

The two isomers of the propylperoxy radical 1-C3H7O2 and 2-C3H7O2, together with their individual rotamers, are identified and assigned by threshold photoelectron spectroscopy with the aid of high-level theoretical computations, from which their accurate adiabatic ionization energies are derived. This study paves the way to probing elusive peroxy radicals and their isomers in advanced mass spectrometry analysis of combustion and atmospheric reactions. [ABSTRACT FROM AUTHOR]

The Cl-initiated oxidation of methacrolein (MACR, C 4 H 6 O) under NO x -free conditions has been investigated in a fast flow tube by using a home-made vacuum ultraviolet (VUV) photoionization mass spectrometer complemented by high-level theoretical calculations. The key species such as intermediates and radicals together with products involved in the oxidation are observed online and confirmed in photoionization mass spectra. The reaction potential energy surfaces of the transient C 4 H 5 O and C 4 H 6 OCl radicals, formed from the hydrogen-abstraction reaction and the addition reaction of MACR with Cl atoms, with oxygen have been theoretically calculated to illuminate the formation of the peroxy radicals of C 4 H 5 OO 2 and C 4 H 6 OClO 2 . The photoionization processes of these peroxy radicals, whose cations are not stable, and their individual self-reactions as well as bimolecular reactions with HO 2 radical are studied and discussed. In addition, kinetic experiments are also performed to get the time evolution of specific products and compared with theoretical models, providing a detailed insight into the reaction mechanism of the Cl-initiated oxidation of MACR.

The two isomers of the propylperoxy radical 1-C 3 H 7 O 2 and 2-C 3 H 7 O 2 , together with their individual rotamers, are identified and assigned by threshold photoelectron spectroscopy with the aid of high-level theoretical computations, from which their accurate adiabatic ionization energies are derived. This study paves the way to probing elusive peroxy radicals and their isomers in advanced mass spectrometry analysis of combustion and atmospheric reactions.

The n -propyl peroxy radical ( n -C 3 H 7 O 2 ) is the key intermediate during atmospheric oxidation of propane (C 3 H 8 ) which plays an important role in the carbon and nitrogen cycles in the troposphere. In this paper, a comprehensive theoretical study on the reaction mechanism and kinetics of the reaction between HO 2 and n -C 3 H 7 O 2 was performed at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311G(d,p) level of theory. Computational results show that the HO 2 + n -C 3 H 7 O 2 reaction proceeds on both singlet and triplet potential energy surfaces (PESs). From an energetic point of view, the formation of C 3 H 7 O 2 H and 3 O 2 via triplet hydrogen abstraction is the most favorable channel while other product channels are negligible. In addition, the calculated rate constants for the title reaction over the temperature range of 238-398 K were calculated by the multiconformer transition state theory (MC-TST), and the calculated rate constants show a negative temperature dependence. The contributions of the other four reaction channels to the total rate constant are negligible., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The vacuum ultraviolet (VUV) photoionization and dissociative photoionization of CH3Cl in the energy range of 11-17 eV have been investigated in detail by combining synchrotron radiation and double imaging photoelectron photoion coincidences (i(2)PEPICO). Three low-lying electronic states of the CH3Cl(+) molecular ion, X(2)E, A(2)A1 and B(2)E, were prepared and analyzed. The appearance energies of the energetically accessible fragment ions, CH2Cl(+), CHCl(+), CH3(+) and CH2(+), have been obtained from their respective mass-selected threshold photoelectron spectra (TPES) or photoionization efficiency (PIE) curves. The dissociation mechanisms of energy-selected CH3Cl(+) ions, prepared in the A(2)A1 and the B(2)E electronic states, as well as outside the Franck-Condon region, have been revealed to be state-specific via ion/electron kinetic energy correlation diagrams. In particular, the umbrella mode vibrational progression of the CH3(+) fragment ion in the direct dissociation of the A(2)A1 electronic state was identified and assigned indicating that this state correlates to the CH3(+)(1(1)A1') + Cl((2)P1/2) dissociation limit, in agreement with the theoretical calculations performed in this work.