Rubo Zhang

Toward high performance indacenodithiophene-based small-molecule organic solar cells: investigation of the effect of fused aromatic bridges on the device performance

Here we report the synthesis of a pair of D1–A-bridge–D2-bridge–A–D1 type small molecules BIT4FDT and BIT4FTT which have different π-conjugated bridges between indacenodithiophene (IDT) as the electron-donating core and the electron-deficient difluorobenzothiadiazole unit and investigated the effects of the π-conjugated bridges on their photovoltaic properties. We found that the molecule BIT4FTT, containing thieno[3,2-b]thiophene which has two fused thiophene rings as the π-conjugated bridges, exhibits different photophysical properties, HOMO/LUMO energy levels, charge carrier mobilities and morphologies of blend films, and photovoltaic properties compared with the analogous system BIT4FDT which has 2,2′-bithiophene rings as the conjugated bridges. Moreover, the devices based on the two molecules after CH2Cl2 solvent annealing exhibited superior device performance to those not subjected to CH2Cl2 solvent annealing. The PCE of BHJ-OSC devices based on BIT4FTT and PC71BM increased from 5.85% to 7.57% (Jsc = 11.33 mA cm−2, Voc = 0.89 V, and FF = 0.75) after exposure to CH2Cl2 vapor due to the obvious increase of both Jsc and FF. Interestingly, the devices based on BIT4FDT and PC71BM showed a weaker response to solvent vapor annealing and much lower PCEs in comparison with those based on BIT4FTT. The results indicate that highly efficient small-molecule solar cells can be achieved using fused aromatic bridges and a suitable solvent vapor annealing process.

The Crystal Structure and Morphology of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) p-Xylene Solvate: A Joint Experimental and Simulation Study

The crystal structure of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaiso-wurtzitane (CL-20) p-xylene solvate, and the solvent effects on the crystal faces of CL-20 were studied through a combined experimental and theoretical method. The properties were analyzed by thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).The growth morphology of CL-20p-xylene solvate crystal was predicted with a modified attachment energy model. The crystal structure of CL-20p-xylene solvate belonged to the Pbca space group with the unit cell parameters, a = 8.0704(12) Å, b=13.4095(20) Å, c = 33.0817(49) Å, and Z = 4, which indicated that the p-xylene solvent molecules could enter the crystal lattice of CL-20 and thus the CL-20 p-xylene solvate is formed. According to the solvent-effected attachment energy calculations, (002) and (11−1) faces should not be visible at all, while the percentage area of the (011) face could be increased from 7.81% in vacuum to 12.51% in p-xylene solution. The predicted results from the modified attachment energy model agreed very well with the observed morphology of crystals grown from p-xylene solution.

A comparative study of the structure, energetic performance and stability of nitro-NNO-azoxy substituted explosives

2,4-Dinitro-NNO-azoxytoluene and 2,6-dinitro-4-nitro-NNO-azoxytoluene were synthesized as energetic compounds. Their structures and properties were studied by X-ray diffractometry, nuclear magnetic resonance and infrared spectroscopy. The differences between the nitro-NNO-azoxy and nitro groups are discussed. The detonation properties, as predicted using EXPLO5, indicate that the detonation velocity and pressure of 2,4-dinitro-NNO-azoxytoluene were greater by 21.7% and 74.3%, respectively, than those of 2,4-dinitrotoluene. Nucleus independent chemical shift analysis was used to investigate skeleton aromaticity and the effect of the nitro-NNO-azoxy and nitro groups on ring aromaticity. Electrostatic potential, bond dissociation energy, Mulliken charges and Wiberg bond order were estimated by density functional theory to establish the molecular electron distribution and stabilities of the compounds. The nitro-NNO-azoxy group has a stronger electron-withdrawing property than that of the nitro group.

Thermal stability of the N10 compound with extended nitrogen chain

1,1′-Azobis(tetrazole) (N10) as a potential eco-friendly material, has the highest nitrogen content among the azo-stabilized poly-nitrogen compounds. The detailed potential energy surface of N10 was thoroughly investigated using M06-2X, MP2 and CCSD(T) calculations, and the main decomposition pathways were calculated by canonical transition state theory modeling. Amongst all the channels studied, ring opening of the N10 compound, followed by N2 elimination to form the linear molecule Im8 is predicted to be the primary decomposition channel. The linear species formed (Im8) is characterized by a successive four-nitrogen atom chain stabilized by two terminal HNC groups. Its thorough decomposition reaction is strongly exothermic with a barrier height of 67.5 kcal mol−1. TST calculations were performed to probe the influence of temperature on the rate coefficients at 1 atm. Based on the thermal decomposition mechanism of N10, the novel species N12 and N14 were explored. These longer nitrogen chain compounds having higher nitrogen content than N10 are strongly expected to improve performance of high energy density materials. It is found that the predicted structures could exist at room temperature by comparison of their energetic barriers with the corresponding primary N2-elimination reaction of N10.

Thermal stability of p-dimethylaminophenylpentazole

The thermal stability of p-dimethylaminophenylpentazole (1) in the solid phase has been thoroughly investigated. The decomposition process of 1 has been verified by a combination of differential scanning calorimetry (DSC), thin-layer chromatography (TLC), temperature-programmed FTIR, and Raman spectroscopy. FTIR and Raman spectra were also calculated to corroborate the results. It was found that 1 could be handled below 20 °C without any obvious deterioration, but it decomposed sharply at 56 °C. The calculated FTIR and Raman vibrational frequencies were in accord with the experimental values.

Endoplasmic Reticulum-Directed Ratiometric Fluorescent Probe for Quantitive Detection of Basal H2O2

The endoplasmic reticulum (ER) has a central role in the fine-tuning of environmental and internal stimuli. We herein report a ratiometric fluorescent probe, α-Naph, capable of determining basal H2O2 in the ER. The probe specifically responds to H2O2. The limit of detection of the probe is as low as 38 nM, making it a feasible sensor to image intracellular basal H2O2. In addition, utilizing its ratiometric property, we are able to measure the concentration of H2O2 in the ER quantitatively, eliminating the error caused by the probe concentration and environment. The intracellular concentration of H2O2 in the ER is calculated to be 0.692 μM under normal conditions and 1.26 μM under the stimulation of phorbol myristate acetate.

Alternative role of cisplatin in DNA damage – theoretical studies on the influence of excess electrons on the cisplatin–DNA complex

Reliable DFT calculations were used to gain insights into the effects of excess electrons on the cisplatin–DNA complex in a water solution. One electron injection is enough to break the two Pt–N7 bonds, which is driven by the rare symmetrical in-plane bending vibration. The dissociated [Pt(NH3)2]+˙ group from the cisplatin–DNA complex could combine with H2O in the surroundings to form a reactive species, which can abstract the most solvent accessible H4′ of the sugar with a barrier of ca. 17.5 kcal mol−1. Upon influence of the multiple electrons addition, the H4′-abstraction reaction by the stable radical anion is feasible with a lower barrier and is exothermic. Thereby, they have high efficiency for DNA damage. The synergic effect between the metal and the ligand is highlighted due to failure of the isolated [Pt(NH3)2]+˙ and [Pt(NH3)2]−˙ to abstract H4′ of sugar because the overlap between the SOMO (on Pt) and the C4′H4′ anti-bonding orbital is zero. In the present studies, an alternate role of cisplatin in DNA damage was discovered, which strongly confirmed that the cisplatin–DNA complex is more vulnerable to attack from low-energy electrons.

Novel [NF2O]+ and [N3NFO]+-based energetic oxidizers for solid propellants with super high specific impulse

Novel [NF2O]+ and [N3NFO]+-based energetic oxidizers were designed, and their structures, thermal stabilities, and energetic properties were investigated via density functional theory (DFT). The analysis of the bond dissociation energies (from 93.4 to 120.8 kcal mol−1) for the screened salts suggests that they possess better thermal stabilities than the reported [NF2O]+SbF6− (89.8 kcal mol−1), and compound 5 was the most stable energetic salt. All the screened salts possess a positive oxygen balance ranging from 13% to 50%. Due to a positive oxygen balance, the specific impulses of the compounds 5, 11–14 (>300 s) were superior to those of ammonium perchlorate (AP) and ammonium dinitramide (ADN) when the optimized ratio of oxidizer/aluminium/PBAN (%) was 76 : 10 : 14. Considering their thermal stability and chemical reactivity, compounds 5 and 11 with super high specific impulses can be regarded as excellent candidates for novel potential solid propellants.

Solid-state Reaction of Azolium Hydrohalogen Salts with Silver Dicyanamide – Unexpected Formation of Cyanoguanidine-azoles, Reaction Mechanism and Their Hypergolic Properties

Cyanoguanidines as well as azoles are important bioactive groups, which play an important role in the medical application; meanwhile, the high nitrogen content makes them excellent backbones for energetic materials. A Novel and simple method that combined these two fragments into one molecular compound was developed through the transformation of dicyanamide ionic salts. In return, compounds 4–11 were synthesized, and fully characterized by IR, MS, NMR and elemental analysis. Meanwhile, the structures of compounds 4, 8 and 11 were confirmed by X-ray crystal diffraction. Detailed reaction mechanisms were studied through accurate calculations on the reaction energy profiles of the azolium cations and DCA anion, which revealed the essence of the transformation proceeding. Meanwhile, compound 8 exhibits excellent hypergolic property, which could be potentially novel molecular hypergolic fuel.

Towards understanding the stability of the N5+-containing salts: the role of counterions

The thermal stabilities of the N5+M− species (M = Sb(OH)6, Sb(OH)4F2, AlF6, AlF4, BF4, B(CF3)4, PF6, AsF6 and SbF6) have been studied by means of density functional theory. The present calculations indicate that their thermal stabilities (represented by activation enthalpy, ΔH≠ in kcal mol−1) decrease in the order N5+ (47.2) > N5B(CF3)4 (34.1) ≈ N5SbF6 (31.6) ≈ N5AsF6 (31.5) > N5PF6 (30.5) > N5AlF4 (27.1) ≈ N5BF4 (27.1) > N5AlF6 (8.5). Only N5SbF6 has a small positive reaction enthalpy, ΔrH. The thermal stability of the N5+ salt depends on the amount of electron transfer from the counterion to N5+ in the reaction. The high electronegativite atoms or groups in the counterion are essential. Another crucial factor is bond strength between the central ion and the ligand. Studies of the N5Sb(OH)4F2 isomers indicate that the OH rather than the fluorine ions in the axial coordination positions could stabilize the decomposition transition structure through partial dissociation of the Sb–OH bond, which is used to explain the reason why there is an obvious difference in the decomposition activation enthalpies of the three isomers.