Nitrogen Fixation by Benzene into Pyridine and Aniline in Water/Nitrogen Plasma.

We demonstrated direct conversion of benzene into pyridine and aniline, assisted through exact mass measurements (m/z 80.0494, 93.0574, and 94.0651, respectively), through the interaction of benzene with water/nitrogen vapor plasma produced by corona discharge. Systematic analysis using a series of isotopic standards indicated that formation of pyridine and aniline occurred through the reaction between neutral benzene and reactive N+(OH2)2 in water/nitrogen plasma; exact mass measurements of products and intermediates supported this hypothesis. As the proportion of water vapor in plasma increased over time, the reaction proceeded from exclusive formation of protonated pyridine to formation of protonated aniline as the main product; theoretical simulations indicated that the presence of water vapor promoted proton migration to elicit formation of protonated aniline. The reactions we discovered suggest a new mechanism for direct nitrogen fixation.

Evidence for the co-existence of isomers of water dimer radical cations and their inter-conversion in a linear ion trap.

Water dimer radical cations are regarded as key intermediates in many aqueous reactions and biochemical processes. However, the structure of the water dimer radical cations, and particularly the inter-conversion between their isomers, remain difficult to investigate experimentally due to their short lifetime and low abundance under ambient conditions. Furthermore, the isomers cannot be distinguished in a full mass spectra. In this study, we report the experimental evidence for the hemi-bonded and proton-transferred isomers of gas-phase water dimer radical cations, and the inter-conversion process between them in a linear ion trap at low pressure and near room temperature. Multiple collisions of isolated water dimer radical cations with He inside the ion trap were systematically investigated; first, under different trapping times (i.e., reaction times) ranging from 0.03 to 800 ms, and then at a very low collision energies ranging from 0.1% to 10% normalized collision energy. The proton-transferred isomers were dominant at shorter trapping times (≤250 ms), while the hemi-bonded isomers were dominant at longer trapping times (250-800 ms). Moreover, the difference in symmetry of the shapes of the H2O•+ signal profiles and the H3O+ signal profiles implied the existence of two kinds of isomers and there were small potential differences between them. Our results also suggested that by tuning the experimental parameters the hemi-bonded isomers would become dominant, which could allow the study of novel chemical reactions involving the hemi-bonded two-center-three-electron (2c-3e) structure in a linear ion trap.

Formation of protonated water-hydrogen clusters in an ion trap mass spectrometer at room temperature.

Protonated water-hydrogen clusters [H+(H2O)n·m(H2)] present an interesting model for fundamental water research, but their formation and isolation presents considerable experimental challenges. Here, we report the detection of [H+(H2O)n·m(H2)] (2 ≤ n ≤ 3, m ≤ 2) clusters alongside protonated water clusters H+(H2O)n (2 ≤ n ≤ 3) in a linear ion trap mass spectrometer under two different experimental conditions: (1) when water vapor was ionized by +5.5 kV ambient corona discharge in front of the mass spectrometer inlet; (2) when isolated H+(H2O)n clusters were exposed to H2 gas inside the linear trap. Chemical assignment of [H+(H2O)n·m(H2)] clusters was confirmed using reference experiments with isotopically labeled water and deuterium. Also, the formation of H2 gas in the corona discharge area was indicated by a flame test. Overall, our findings clearly indicate that [H+(H2O)n·m(H2)] clusters can be produced at room temperature through the association of protonated water clusters H+(H2O)n with H2 gas, without any cooling necessary. A mechanism for the formation of the protonated water-hydrogen complexes was proposed. Our results also suggest that the association of water ions with H2 gas may play a notable role in corona discharge ionization processes, such as atmospheric pressure chemical ionization, and may be partially responsible for the stabilization of reactive radical species occasionally reported in corona discharge ionization experiments.

Generation of Phenol and Molecular Hydrogen through Catalyst-Free C-H Activation of Benzene by Water Radical Cations.

Here, we report on the abundant formation of phenol and molecular hydrogen when benzene vapor was exposed to gas plasma generated by +5.5 kV corona discharge of water vapor in argon in the absence of oxygen. Systematic analysis using a series of isotopic standards (d6-benzene, D2O, and H218O) and benzene derivatives (mono-, di-, trichlorobenzene, and N,N-dimethylaniline) indicated that the formation of phenol occurred through the reaction between neutral benzene and the radical cation of water dimer, (H2O)2+•. A two-step reaction mechanism was proposed based on the results of experiments and DFT calculations: (1) the formation of (C6H6...H2O)+• intermediate through electrophilic addition; (2) the formation of C6H5OH+• through the release of H2 from the (C6H6...H2O)+• intermediate. Our findings offer a novel catalyst-free method to prepare phenol from benzene with phenol selectivity >90%.

Water Radical Cations in the Gas Phase: Methods and Mechanisms of Formation, Structure and Chemical Properties.

Water radical cations, (H2O)n+•, are of great research interest in both fundamental and applied sciences. Fundamental studies of water radical reactions are important to better understand the mechanisms of natural processes, such as proton transfer in aqueous solutions, the formation of hydrogen bonds and DNA damage, as well as for the discovery of new gas-phase reactions and products. In applied science, the interest in water radicals is prompted by their potential in radiobiology and as a source of primary ions for selective and sensitive chemical ionization. However, in contrast to protonated water clusters, (H2O)nH+, which are relatively easy to generate and isolate in experiments, the generation and isolation of radical water clusters, (H2O)n+•, is tremendously difficult due to their ultra-high reactivity. This review focuses on the current knowledge and unknowns regarding (H2O)n+• species, including the methods and mechanisms of their formation, structure and chemical properties.

Ternary Nonfullerene Polymer Solar Cells with 12.16% Efficiency by Introducing One Acceptor with Cascading Energy Level and Complementary Absorption.

A novel small-molecule acceptor, (2,2'-((5E,5'E)-5,5'-((5,5'-(4,4,9,9-tetrakis(5-hexylthiophen-2-yl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(4-(2-ethylhexyl)thiophene-5,2-diyl))bis(methanylylidene)) bis(3-hexyl-4-oxothiazolidine-5,2-diylidene))dimalononitrile (ITCN), end-capped with electron-deficient 2-(3-hexyl-4-oxothiazolidin-2-ylidene)malononitrile groups, is designed, synthesized, and used as the third component in fullerene-free ternary polymer solar cells (PSCs). The cascaded energy-level structure enabled by the newly designed acceptor is beneficial to the carrier transport and separation. Meanwhile, the three materials show a complementary absorption in the visible region, resulting in efficient light harvesting. Hence, the PBDB-T:ITCN:IT-M ternary PSCs possess a high short-circuit current density (Jsc ) under an optimal weight ratio of donors and acceptors. Moreover, the open-circuit voltage (Voc ) of the ternary PSCs is enhanced with an increase of the third acceptor ITCN content, which is attributed to the higher lowest unoccupied molecular orbital energy level of ITCN than that of IT-M, thus exhibits a higher Voc in PBDB-T:ITCN binary system. Ultimately, the ternary PSCs achieve a power conversion efficiency of 12.16%, which is higher than the PBDB-T:ITM-based PSCs (10.89%) and PBDB-T:ITCN-based ones (2.21%). This work provides an effective strategy to improve the photovoltaic performance of PSCs.

Novel "hot exciton" blue fluorophores for high performance fluorescent/phosphorescent hybrid white organic light-emitting diodes with superhigh phosphorescent dopant concentration and improved efficiency roll-off.

Two blue fluorophores with excellent hybridized local and charge-transfer (HLCT) and "hot exciton" properties were developed as the blue emitter and the host for orange-red phosphor to achieve highly efficient fluorescent/phosphorescent (F/P) hybrid white organic light-emitting diodes (WOLEDs) in a single-emissive-layer single-dopant (SEML-SD) architecture even at a high concentration of phosphorescent dopant. In the devices, part of the triplet excitons of the blue fluorophores can be utilized to realize reverse intersystem crossing from the triplet excited states to the singlet excited states for blue emission, and the diffusion volume range of the triplet excitons is reduced significantly. When the phosphorescent dopant concentration is up to 1.0 wt %, which is ten times higher than the traditional single-EML-SD F/P hybrid WOLEDs, highly efficient white emission was still achieved with maximum total external quantum efficiency (EQE) of 23.8%, current efficiency (CE) of 56.1 cd A(-1), and power efficiency (PE) of 62.9 lm W(1-). The results will supply a novel method for obtaining high efficiency F/P hybrid WOLEDs in a SEML-SD architecture with easily controllable doping concentration.

Fullerene derivatives as electron acceptors for organic photovoltaic cells.

Energy is currently one of the most important problems humankind faces. Depletion of traditional energy sources such as coal and oil results in the need to develop new ways to create, transport, and store electricity. In this regard, the sun, which can be considered as a giant nuclear fusion reactor, represents the most powerful source of energy available in our solar system. For photovoltaic cells to gain widespread acceptance as a source of clean and renewable energy, the cost per watt of solar energy must be decreased. Organic photovoltaic cells, developed in the past two decades, have potential as alternatives to traditional inorganic semiconductor photovoltaic cells, which suffer from high environmental pollution and energy consumption during production. Organic photovoltaic cells are composed of a blended film of a conjugated-polymer donor and a soluble fullerene-derivative acceptor sandwiched between a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-coated indium tin oxide positive electrode and a low-work-function metal negative electrode. Considerable research efforts aim at designing and synthesizing novel fullerene derivatives as electron acceptors with up-raised lowest unoccupied molecular orbital energy, better light-harvesting properties, higher electron mobility, and better miscibility with the polymer donor for improving the power conversion efficiency of the organic photovoltaic cells. In this paper, we systematically review novel fullerene acceptors synthesized through chemical modification for enhancing the photovoltaic performance by increasing open-circuit voltage, short-circuit current, and fill factor, which determine the performance of organic photovoltaic cells.

Synthesis and properties of new low band gap semiconducting polymers.

Low band gap organic semiconducting polymers were prepared as p-type donors for organic photovoltaic devices. A novel dibrominated monomer composed of phenothiazine, thiophene, and benzothiadiazole (DPDTBT) was synthesized as a low band gap core block. DPDTBT was copolymerized with three different boronic esters of dithiophene, fluorene, and phenothiazine by the Suzuki coupling polycondensation reaction. The band gap energies of the synthesized polymers ranged between 2.05 and 2.11 eV, depending on the polymer structure. Bulk heterojunction solar cells fabricated using the polymers and [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) as an acceptor were characterized. The best power conversion efficiency obtained from the fabricated devices under simulated AM 1.5 G solar irradiation of 100 mW/cm2 was 0.46%.

Synthesis and characterization of novel soluble fulleropyrrolidine derivatives and their photovoltaic performance.

Currently, [60] fullerene derivatives are the focus of considerable research due to their important roles in many fields, especially material science. In this study, we synthesized the following two novel fulleropyrrolidine derivatives: C60-fused N-methyl-(4-hexyloxybenzen-2-yl) pyrrolidine, (p-HOPF) and C60-fused N-methyl-(2-hexyloxybenzen-2-yl) pyrrolidine, (o-HOPF). Structural assignments of the two fullerene derivatives were made through 1H NMR and FAB-MS. We also measured the optical and electrochemical properties of p-HOPF and o-HOPF through UV/Vis spectrophotometry and cyclic voltammetry. We found that the difference in the position of the alkoxyl substituent on the phenyl ring greatly affects the characteristics of the molecules. In particular, from the 1H NMR spectrum, we found that the hydrogen atoms on the carbons adjacent to the oxygens in p-HOPF and o-HOPF have completely different chemical environments. In order to study the effects of the substituent group positions on photovoltaic performance, photovoltaic devices were fabricated. The highest power conversion efficiency, 0.71%, was achieved when using o-HOPF as the electron acceptor.

Synthesis and properties of copolymers composed of arylenevinylene and phenothiazine for organic solar cells.

A series of new organic semiconducting copolymers composed of {(2E,2'E)-3,3'-[2,5-bis(octyloxy)-1,4-phenylene]-bis[2-(thiophen-2-yl)acrylonitrile]}(OPTAN) and 10(2'-ethylhexylphenothiazine) (PTZ) monomers, (the copolymers are hereafter referred to as poly(OPTAN-co-PTZ)s), were synthesized by using Suzuki coupling polymerization in which the monomer ratios were controlled. An increase in the OPTAN content shifted the peak and onset absorption of the copolymers to the longer wavelength regions, which resulted in a decrease in the band gap energy. The maximum UV absorption of the polymer films was in the range 523-540 nm and the optical band gap energies were in the range 1.90-1.87 eV. Energy levels of the highest occupied molecular orbital (HOMO) of the polymers were determined by cyclic voltammetry (CV). The HOMO energy level of the copolymers was between -5.07 and -5.12 eV. Photovoltaic devices were fabricated by using the copolymers as the p-type donor and C60-PCBM or C70-PCBM as the electron acceptors. The device with poly(50OPTAN-alt-50PTZ) and C70-PCBM showed the best performance among the fabricated devices; the open circuit voltage, short circuit current, fill factor, and maximum power conversion efficiency of this device were 0.79 V, 5.25 mA/cm2, 0.30, and 1.25%, respectively.

Synthesis and properties of a polyhedral oligomeric silsesquioxane-based new light-emitting nanoparticle.

A polyhedral oligomeric silsesquioxane (POSS)-based electroluminescent nanoparticle, POSS-NPA, which contains anthracenenaphthyl chromophores on each of its eight arms, was easily prepared via the hydrosilylation reaction between octakis(dimethylsiloxy)silsesquioxane and allyl-functionalized 9-naphthalene-2-yl-10-phenyl anthracene chromophores. POSS-NPA was completely soluble in common organic solvents such as chloroform, THF, toluene, p-xylene, and chlorobenzene, and showed good film-forming properties on a quartz plate or an indium tin oxide (ITO) plate, i.e., it has good solution processing properties. The UV-visible absorption and the photoluminescence (PL) emission maxima of POSS-NPA in chlorobenzene solution were found to be 378 nm and 433 nm while those of POSS-NPA in the solid state were 379 and 464 nm, respectively. An electroluminescent (EL) device with the configuration of ITO/PEDOT:PSS/POSS-NPA (50 nm)/BAIq (40 nm)/LiF (1 nm)/Al (120 nm) was also fabricated and the blue light emission was successfully obtained.