Junkuo Gao

Synthesis, characterization, and nonvolatile ternary memory behavior of a larger heteroacene with nine linearly fused rings and two different heteroatoms.

To achieve ultrahigh density memory devices with the capacity of 3(n) or larger, organic materials with multilevel stable states are highly desirable. Here, we reported a novel larger stable heteroacene, 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-6,10,17,21-tetrachloro-7,9,18,20-tetraoxa-8,19-dicyanoenneacene (CDPzN), which has two different types of heteroatoms (O and N) and nine linearly fused rings. The sandwich-structure memory devices based on CDPzN exhibited excellent ternary memory behaviors with high ON2/ON1/OFF current ratios of 10(6.3)/10(4.3)/1 and good stability for these three states.

Synthesis and Physical Properties of Four Hexazapentacene Derivatives

In two steps from commercially available starting materials, four novel hexazapentacene derivatives have been synthesized through cyclocondensation reaction between tetraamines and 1,2-diketones. The observed optical bandgaps for 2,3,9,10-tetramethyl-1,4,6,8,11,13-hexaza-pentacene (TMHAP, 1), tetraethyl-1,4,6,8,11,13-hexaza-pentacene (TEHAP, 2), 1,2,3,4,10,11,12,13-octahydro-5,7, 9,14,16,18-hexazaheptacene (OHHAH, 3), and tetra(2-thioyl)-1,4,6,8,11,13-hexazapentacene (TTHAP, 4) are 2.55, 2.55, 2.45, and 2.25 eV, respectively. The cyclic voltammetry measurements show that all compounds exhibit one revisable reduction waves. The calculated bandgaps through DFT calculations for TMHAP (1), TEHAP (2), OHAH (3), and TTHAP (4) are 2.41, 2.41, 2.34, and 2.15 eV, respectivly, which are close to the experimental results. Our success in synthesizing hexazapentacene derivatives might offer a promising strategy to challenge larger azaacenes with more N atoms.

Direct Synthesis of Porous Nanorod-Type Graphitic Carbon Nitride/CuO Composite from Cu-Melamine Supramolecular Framework towards Enhanced Photocatalytic Performance.

Facile and direct synthesis of porous nanorod-type graphitic carbon nitride/CuO composite (CuO-g-C3 N4 ) has been achieved by using a Cu-melamine supramolecular framework as a precursor. The CuO-g-C3 N4 nanocomposite demonstrated improved visible-light-driven photocatalytic activities. The results indicate that metal-melamine supramolecular frameworks can be promising precursors for the preparation of efficient g-C3 N4 nanocomposite photocatalysts.

Metal–organic framework nanosheets for fast-response and highly sensitive luminescent sensing of Fe3+

The first luminescent two-dimensional MOF nanosheets NTU-9-NS Ti2(HDOBDC)2(H2DOBDC) (H2DOBDC = 2,5-dihydroxyterephthalic acid) fabricated via top-down delamination have been realized for the highly sensitive sensing of Fe3+ with a fast response. The highly dispersive nature and highly accessible active sites on the surface of the 2D NTU-9-NS nanosheets enable them to have close contact with targeted metal ions, which leads to the highly sensitive sensing of Fe3+ ions, with a fast response time within seconds and the best detection limit performance of 0.45 μM among MOF materials. The fast response and highly sensitive Fe3+ sensing based on the NTU-9-NS nanosheets sensor material highlights the promise of the two-dimensional MOF nanosheet approach for luminescent sensing applications. This work contributes to the development of research on two-dimensional MOF nanosheets materials with targeted and specific recognition for the application of biological and environmental luminescent sensors.

Inorganic–organic hybrid polymer with multiple redox for high-density data storage

Although organic multilevel resistance memories have attracted much attention for potential realization of the exponentially-increasing density of data storage, the ambiguous structure–property relationship and the unclear switching mechanism impeded further development of multilevel resistance memory devices. Therefore, it is very urgent to ingeniously design multilevel memory materials with a certain switching mechanism. In this contribution, we have employed a multi-redox (multiple barriers) polyoxometalate-based inorganic–organic hybrid polymer (whose effective carriers are electrically controllable) to realize a ternary resistance switching memory (multilevel memories). We do believe that the as-designed inorganic–organic polymer can integrate the multi-redox states of the POM and the processability of flexible polymers together. The as-fabricated multilevel memory devices exhibit rewriteable switching properties among three redox states by applying different RESET voltages, good endurance with distinct operation windows, and long retention. Our results could provide a new strategy to design controllable multilevel resistance memories with excellent performance.

Surfactant–Thermal Method to Synthesize a Novel Two‐Dimensional Oxochalcogenide

A new two-dimensional (2D) oxosulfide, (N2H4)2Mn3Sb4S8(μ3-OH)2 (1), has been successfully synthesized under surfactant-thermal conditions with hexadecyltributylphosphonium bromide as the surfactant. Compound 1 has a layered structure and contains a novel [Mn3(μ3-OH)2]n chain along the b-axis. The photocatalytic activity for compound 1 has been demonstrated under visible-light irradiation and continuous H2 evolution was observed. Our results indicate that surfactant-thermal synthesis could be a promising method for growing novel crystalline oxochalcogenides with interesting structures and properties.

[4 + 2] cycloaddition reaction to approach diazatwistpentacenes: synthesis, structures, physical properties, and self-assembly.

Three novel diazatwistpentacenes (1,4,6,13-tetraphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (1, IUPAC name: 9,11,14,16-tetraphenyl-1,6-dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine); 1,4-di(pyridin-2-yl)-6,13-diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (2, IUPAC name: 9,16-diphenyl-11,14-di(pyridin-2-yl)-1,6-dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine); and 1,4-di(thien-2-yl)-6,13-diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (3, IUPAC name: 9,16-diphenyl-11,14-di(thien-2-yl)-1,6-dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine)) have been successfully synthesized through [4 + 2] cycloaddition reaction involving in situ arynes as dienophiles and substituted 1,2,4,5-tetrazines as dienes. Their structures have been determined by single-crystal X-ray diffraction, confirming that all compounds have twisted configurations with torsion angles between the pyrene unit and the 2,3-diazaanthrance part as high as 21.52° (for 1), 24.74° (for 2), and 21.14° (for 3). The optical bandgaps for all compounds corroborate the values derived from CV. The calculation done by DFT shows that the HOMO-LUMO bandgaps are in good agreement with experimental data. Interestingly, the substituted groups (phenyl, pyridyl, thienyl) in the 1,4-positions did affect their self-assembly and the optical properties of as-resulted nanostructures. Under the same conditions, compounds 1-3 could self-assemble into different morphologies such as microrods (for 1), nanoprisms (for 2), and nanobelts (for 3). Moreover, the UV-vis absorption and emission spectra of as-prepared nanostructures were largely red-shifted, indicating J-type aggregation for all materials. Surprisingly, both 1 and 2 showed aggregation-induced emission (AIE) effect, while compound 3 showed aggregation-caused quenching (ACQ) effect. Our method to approach novel twisted azaacenes through [4 + 2] reaction could offer a new tool to develop unusual twisted conjugated materials for future optoelectronic applications.

QM/MM Modeling of Environmental Effects on Electronic Transitions of the FMO Complex

The Fenna-Matthews-Oslon (FMO) light harvesting pigment-protein complex in green sulfur bacteria transfers the excitation energy from absorbed sunlight to the reaction center with almost 100% quantum efficiency. The protein-pigment coupling (part of the environmental effects) is believed to play an important role in determining excitation energy transfer pathways. To study the effect of environment on the electronic transitions in the FMO complex, especially by taking into account the newly discovered eighth extra pigment, we have employed hybrid quantum-mechanics/molecular-mechanics (QM/MM) methods in combination with molecular dynamics (MD) simulations. The averaged site energies of individual pigments are calculated using the semiempirical ZINDO/S-CIS method considering the protein residues as atomic point charges along the MD trajectories. The exciton energies are calculated from the site energies and excitonic couplings based on MD simulations. The new eighth pigment displays the largest site energy and contributes mainly to the highest exciton level, which may facilitate transfer of excitation energies from the baseplate to the reaction center. Further, the multimode Brownian oscillator (MBO) model is used to fit the linear absorption spectra of the FMO complex, validating the exciton energies obtained from the QM/MM calculations. Our results indicate that the QM/MM method combined with MD simulations is a powerful tool to model the environmental effects on electronic transitions of light harvesting antenna complexes.

High performance single In2Se3 nanowire photodetector

The single In₂Se₃ nanowire photodetectors were fabricated and the performance characteristics of the NW devices were systematically investigated. The single In₂Se₃ NW photodetectors show high and stable photoresponse at wide light wavelength (254-800 nm) and temperature range (7-300 K). The spectra response curve indicates the absorption coefficient of the In₂Se₃ NWs at certain wavelength dominates the performance of the devices. The good linearity of the photocurrents with the incident irradiation over a wide wavelength range has been obtained, indicating the In₂Se₃ nanowire photodetector works under a typical light dependent resistor mode.

Synthesis, physical properties, and self-assembly of a novel asymmetric aroyleneimidazophenazine.

The synthesis, physical properties, and self-assembly of a novel asymmetric aroyleneimidazophenazine (IZ1) is reported. The as-prepared IZ1 nanowires display an obvious red fluorescence. A heterojunction light-emitting diode (LED) device with the structure ITO/IZ1 nanowires/p-SiC/Al (10 nm)/Ti (80 nm)/Al (380 nm)/ITO was fabricated, and electroluminescence emission with two peaks at about 412 nm and 613 nm was detected with a forward bias ranging from 5 to 10 V.