Jinchong Xiao

Synthesis, structure, and optoelectronic properties of a new twistacene 1,2,3,4,6,13-hexaphenyl-7 : 8,11 : 12-bisbenzo-pentacene

We report the synthesis, optical and electrochemical properties, as well as the fabrication of light-emitting devices for a new twistacene 1,2,3,4,6,13-hexaphenyl-7 : 8,11 : 12-bisbenzo-pentacene (HBP 1). Its structure, determined by X-ray crystallography, confirmed that this material has a twisted topology with the torsion angle as high as 23.0°. HBP 1 showed bright green emission both in solution and solid state. The HOMO–LUMO gap of HBP 1 calculated from the difference between the half-wave redox potentials (E1/2ox = +0.74 eV and E1/2red = −1.93 eV) is 2.67 eV, which is in good agreement with the band gap, 2.64 eV, derived from the UV-Vis absorption data. Organic light emitting devices using HBP 1 as the emitters have been fabricated. The results revealed that twistacenes are promising materials to enhance the efficiency of OLEDs.

Synthesis, Structure, and Physical Properties of 5,7,14,16‐Tetraphenyl‐8:9,12:13‐bisbenzo‐hexatwistacene

A novel compound, 5,7,14,16-tetraphenyl-8:9,12:13-bisbenzo-hexatwistacene (TBH), has been successfully synthesized through a retro-Diels-Alder reaction. Single-crystal structure analysis indicated that TBH has a twisted configuration with a torsion angle of 27.34°. The HOMO-LUMO gap of TBH calculated from the difference between the half-wave redox potentials (E(1/2) (ox) =+0.40 eV and E(1/2)(red) =-1.78 eV) is 2.18 eV, which is in good agreement with the band gap (2.19 eV) derived from the UV/Vis absorption data. In addition, organic light-emitting devices using TBH as emitter have been fabricated. The results revealed that TBH is a promising red light-emitting candidate for applications in organic light-emitting diodes.

Synthesis, characterization, self-assembly, and physical properties of 11-methylbenzo[d]pyreno[4,5-b]furan.

Synthesis, structure, and physical properties of a novel 11-methylbenzo[d]pyreno[4,5-b]furan (BPF) and its self-assembly in water have been reported. The performance of nanowire-based films in organic light-emitting diodes is much better than that of the thin film deposited by directly drop-coating BPF molecules in THF solution. SEM study indicates that the well-organized structure (nanowires) is an important factor in enhancing the performance of OLED devices.

Crystal structure and phototransistor behavior of N-substituted heptacence.

6,8,15,17-Tetraaza-1.18,4.5,9.10,13.14-tetrabenzoheptacene (TTH, 1) has been prepared and characterized by single-crystal X-ray structure analysis. A phototransistor device based on TTH single crystal demonstrated that TTH showed a good performance in signal amplification under the photoconductive effect as well as photocontrolled switches.

Preparation, characterization, and photoswitching/light-emitting behaviors of coronene nanowires

Coronene nanowires were prepared through the reprecipitation method. The as-prepared one-dimensional (1D) nanostructures were characterized by UV-vis, fluorescence spectra, X-ray diffraction (XRD), optical microscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). We found that coronene nanowires in aqueous solution emitted strong green light instead of blue light for coronene molecules in THF solution. Moreover, the thin film of coronene nanowires on rGO/SiO2/Si electrode produced a strong photocurrent response upon irradiation. In addition, a heterojunction light emitting diode (LED) device with the structure of quartz/ITO/p-coronene nanowires/n-SiC/Ti (10 nm)/Au (120 nm) has been fabricated. The strong electroluminescence (EL) emission centered at ∼430 nm was detected with a forward bias at 20 V. Our result showed that the use of organic nanowires as the p-type hole injection layer could produce diodes with performance better than those with only inorganic thin-film structures.

Synthesis, Characterization, and Physical Properties of a Conjugated Heteroacene: 2-Methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ)

We report the synthesis and characterization of a novel, stable and blue heteroacene, 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ 3). BIQ 3, with its relatively small π framework, has an absorption λ(max) at 620 nm, which is larger than that of pentacene (λ(max) = 582 nm), but BIQ 3 is more stable. The solutions of BIQ 3 are observed without any noticeable photobleaching on the order of days. In the solid state, it is very stable at ambient conditions and can be stored indefinitely. Owing to its pyridone end unit, BIQ 3 can display different resonance structures in different solvents (aprotic and protic) or Lewis acids to give different colors. The attractive stability exhibited by BIQ 3 is very desirable in organic semiconductor devices. Herein, we investigated a simple heterojunction photovoltaic device based on BIQ 3 as an electron donor and [6,6]-phenyl-C(61) butyric methyl ester as an electron acceptor. Our results show that this type of heteroacene could be a good candidate as a charge-transport material in organic semiconductor devices.

Synthesis, Photophysics, and Self‐Assembly of Furan‐Embedded Heteroarenes

A series of pyrene/phenanthrene-fused furan derivatives (1-8) were synthesized by a simple condensation reaction between pyrene-4,5-diketone/phenanthrenequinone and substituted phenol/naphthol in the presence of trifluoromethanesulfonic acid in 1,2-dichlorobenzene heated at reflux. The formed compounds can emit strong blue light in organic solvents. Additionally, the self-assembly behaviors of two of the compounds (3 and 5) were studied through re-precipitation method and the resulting nanostructures were characterized by UV/Vis, fluorescence spectra, and field-emission scanning electron microscopy (FESEM). The findings showed that the shape and size of compounds 3 and 5 could be tuned by the ratio of THF and hexadecyl trimethyl ammonium bromide (CTAB) solution in water.

Synthesis, Crystal Analyses, Physical Properties, and Electroluminescent Behavior of Unsymmetrical Heterotwistacenes

Four novel unsymmetrical heteroacenes containing five-membered heterocycles (OPyN, TPyN, TPyC, TPyO) have been synthesized and characterized. The formed molecules exhibited twisted structures, determined by crystal analysis and showed blue/green fluorescence in dichloromethane and in thin film. Compounds OPyN and TPyN were selectively used as active ingredients, and the fabricated devices displayed promising electroluminescent performance.

Postchemistry of Organic Microrods: Thermopolymerization in Aqueous Solution

It is well known that solid-state reactions on the micro-/ nanometer scale can happen not only in inorganic particles but also in biological systems (natural particles). Logically, artificial organic micro-/nanostructures should also possess this ability to perform chemical reactions. Establishing this concept may be useful for creating novel organic materials with technological applications and achieving new physical phenomena. As potential next-generation materials for organic electronics, organic semiconductor micro-/nanostructures have recently attracted particular attention in organic devices. Their diverse structures and tunable properties have led to a lot of applications, such as field-effect transistors, chemical sensors, solar cells, memory elements, optical waveguides, lasers, and colour-tunable displays. In particular, conducting polymer micro-/nanostructures have emerged as a new research field to create new smart materials for applications in modern and future technologies. Although many methods such as template-less synthesis, template(hard/soft)-assisted approaches, electro-spinning technology, and molecular-template-assisted synthesis are widely employed to create conducting polymer micro-/nano-structures, using organic microrod precursors as starting materials to generate conducting polymer micro-/nano-materials in water through thermopolymerization is still in its infancy. This unsatisfactory situation is the motivation for this contribution. Solid-state polymerization in bulk pre-organized crystalline precursors has been discovered in several conducting polymer systems. It is reasonable to anticipate that this type of reactions could also be realized on the micro-/nanoscale when the size of the bulk crystalline precursors drops to the micro-/nanometer level. Success in this direction could not only make this concept more useful in nanoelectronics, but also provide a more-fundamental understanding of nano-scale solid-state polymerization. In a complicated nanoelectronic device, the conducting nanowires are required to connect several different nano-units together to perform a more-complicated function. However, as we know, most conducting polymers are not soluble in organic solvents. It is very difficult to pattern them as conducting wires in nanoelectronic devices. But soluble DBEDOT molecules, or similar materials that can perform solid-state polymerization on nano-scale, can be easily patterned into certain positions by dip-pen nanotechnology (DPN) or other fabrication technologies. After polymerization through heat or light, they can perform conducting functions. We believe that our success could make this type of molecules more promising as nano-conducting-wire ink for nanoelectronics. The precursor that we chose for our study is 2,5-dibromo3,4-ethylenedioxythiophene (DBEDOT, Scheme 1), which had been reported by Wudl et al. to perform solid-state polymerization through simply heating crystalline bulk monomers to produce highly conductive self-doped semi-crystalline poly(3,4-ethylenedioxythiophene) (PEDOT). Herein, we report that it is indeed possible to realize the solid-state polymerization of DBEDOT on the micro-scale. [a] Dr. J. Xiao, D. Y. Kusuma, Y. Wu, Prof. F. Boey, Prof. H. Zhang, Prof. P. S. Lee, Prof. Q. Zhang School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798 (Singapore) Fax: (+65) 67909081 E-mail : pslee@ntu.edu.sg qczhang@ntu.edu.sg Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000684. Scheme 1. The structure of DBEDOT.

Synthesis, Single Crystal, and Physical Properties of Asymmetrical Thiophene/Selenophene-Fused Twistacenes.

Two asymmetrical twistacenes, PyPT and PyPS, have been synthesized and characterized. Single crystal X-ray analyses show that both of them have twisted structures with a torsion angle of 26.65° for PyPT and 26.59° for PyPS measured between plane C5-C23-C25 and plane C13-C15-C26. The thiophene/selenophene-fused acenes emit blue fluorescence with quantum yields of 0.39 for PyPT and 0.04 for PyPS in organic solvents, whereas the all-carbon molecule HBP emits green fluorescence. Meanwhile, PyPT and PyPS show a similar reversible oxide procedure with the onset potentials of 0.73 and 0.72 V, respectively. In addition, PyPT and PyPS can self-assemble to form nanoparticles in a mixture of THF/H2O through re-precipitation method.