Linghai Xie

Hydrogen‐Bonded Supramolecular Conjugated Polymer Nanoparticles for White Light‐Emitting Devices

Supramolecular polyfluorenol enable assembly into conjugated polymer nanoparticles (CPNs). Poly{9-[4-(octyloxy)phenyl]fluoren-9-ol-2,7-diyl} (PPFOH)-based supramolecular nanoparticles are prepared via reprecipitation. PPFOH nanoparticles with diameters ranging from 40 to 200 nm are obtained by adding different amounts of water into DMF solution. Size-dependent luminescence is observed in PPFOH-based hydrogen-bonded nanoparticles that is different from that of poly(9,9-dioctylfluorenes). Finally, white light-emitting devices using CPNs with a size of 80 nm exhibit white emission with the CIE coordinates (0.31, 0.34). Amphiphilic conjugated polymer nanoparticles are potential organic nano-inks for the fabrication of organic devices in printed electronics.

Multilayer Stacked Low‐Temperature‐Reduced Graphene Oxide Films: Preparation, Characterization, and Application in Polymer Memory Devices

Highly reduced graphene oxide (rGO) films are fabricated by combining reduction with smeared hydrazine at low temperature (e.g., 100 degrees C) and the multilayer stacking technique. The prepared rGO film, which has a lower sheet resistance ( approximately 160-500 Omega sq(-1)) and higher conductivity (26 S cm(-1)) as compared to other rGO films obtained by commonly used chemical reduction methods, is fully characterized. The effective reduction can be attributed to the large effective reduction depth in the GO films (1.46 microm) and the high C1s/O1s ratio (8.04). By using the above approach, rGO films with a tunable thickness and sheet resistance are achieved. The obtained rGO films are used as electrodes in polymer memory devices, in a configuration of rGO/poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM)/Al, which exhibit an excellent write-once-read-many-times effect and a high ON/OFF current ratio of 10(6).

Spirocyclic aromatic hydrocarbon-based organic nanosheets for eco-friendly aqueous processed thin-film non-volatile memory devices

Supramolecular steric hindrance designs make pyrene-functionalized spiro[fluorene-9,7-dibenzo[c,h]acridine]-5-one (Py-SFDBAO) assemble into 2D nanostructures that facilitate aqueous phase large-area synthesis of high-quality and uniform crystalline thin films. Thin-film diodes using aqueous nanosheets as active layers exhibit a non-volatile bistable electrical switching feature with ON/OFF ratios of 6.0 × 10(4) and photoswitching with conductive gains of 10(2) -10(3). Organic nanosheets are potentially key components for eco-friendly aqueous dispersed organic nano-inks in the application of printed and flexible electronics.

Synthesis of Fluoren-9-ones and Ladder-Type Oligo-p-phenylene Cores via Pd-Catalyzed Carbonylative Multiple C–C Bond Formation

A new route to various substituted fluoren-9-ones has been developed via an efficient Pd-catalyzed carbonylative multiple C-C bond formation. Under a CO atmosphere, using commercially available aryl halides and arylboronic acids as substrates, this three-component reaction proceeded smoothly in moderate to excellent yields with good functional-group compatibility. The mechanistic investigations suggested a sequential process for the reaction that forms o-bromobiaryls in the first stage followed by a cyclocarbonylation reaction. This chemistry has been successfully extended to construct ladder-type oligo-p-phenylene cores.

Palladium-catalyzed direct arylation of C-H bond to construct quaternary carbon centers: the synthesis of diarylfluorene.

A novel Pd-catalyzed C-H functionalization reaction was developed to construct a quaternary carbon center with high yield. This reaction provides an efficient method for the synthesis of 9,9-diarylfluorenes by direct arylation of monoarylfluorene.

Electrical characteristics and carrier transport mechanisms of write-once-read-many-times memory elements based on graphene oxide diodes

We demonstrated write-once-read-many-times (WORM) memory devices based on graphene oxide (GO) film sandwiched between ITO and LiF/Al electrode. The devices showed irreversible electrical transition from the low conductivity (OFF) state to the high conductivity (ON) state and the ON/OFF current ratio between the conductivities of two states was over 5.7u2009×u2009104. The results of I-V data, AFM and SEM images indicated that the WORM memory characteristics of GO diodes were mainly attributed to charge trapping at GO layers and interfacial properties between GO and LiF/Al electrode.

The mechanical bending effect and mechanism of high performance and low-voltage flexible organic thin-film transistors with a cross-linked PVP dielectric layer

Low operational voltage flexible organic thin-film transistors (OTFTs) have been achieved using two layers of cross-linked PVP as the dielectric layer on a flexible polyimide (PI) substrate. At low operating voltages of −4 V, the flexible OTFTs showed good performances with high field-effect mobility (∼0.56 cm2 V−1 s−1), low threshold voltage (∼−0.82 V), high on/off current ratio (∼105) and excellent electrical stability (∼2 months). During a severe mechanical bending test (104 bending cycles and a bending radius of 0.75 mm) under ambient conditions, the flexible OTFTs still showed excellent electrical performance at the low operational voltage. Moreover, the effects of the mechanical bending on the electrical parameters of the flexible OTFTs were also systematically investigated. We found that the variations of the electrical parameters of the flexible OTFTs during the mechanical bending process were closely related to the distance effect of the spacing between stretched pentacene molecules and the doping effect of H2O and O2 which were induced by the mechanical bending strains. In comparison with previously reported flexible OTFTs, the research results showed that the distance effect and doping effect were mutually independent as well as mutually related during the mechanical bending process of the flexible OTFTs.

Fluorene-based macromolecular nanostructures and nanomaterials for organic (opto)electronics.

Nanotechnology not only opens up the realm of nanoelectronics and nanophotonics, but also upgrades organic thin-film electronics and optoelectronics. In this review, we introduce polymer semiconductors and plastic electronics briefly, followed by various top-down and bottom-up nano approaches to organic electronics. Subsequently, we highlight the progress in polyfluorene-based nanoparticles and nanowires (nanofibres), their tunable optoelectronic properties as well as their applications in polymer light-emitting devices, solar cells, field-effect transistors, photodetectors, lasers, optical waveguides and others. Finally, an outlook is given with regard to four-element complex devices via organic nanotechnology and molecular manufacturing that will spread to areas such as organic mechatronics in the framework of robotic-directed science and technology.

Synthesis and Crystal Structure of Highly Strained [4]Cyclofluorene: Green-Emitting Fluorophore

[4]Cyclo-9,9-dipropyl-2,7-fluorene ([4]CF) with the strain energy of 79.8 kcal/mol is synthesized in high quantum yield. Impressively, hoop-shaped [4]CF exhibits a green fluorescence emission around 512 nm offering a new explanation for the green band (g-band) in polyfluorenes. The solution-processed [4]CF-based organic light emitting diode (OLED) has also been fabricated with the a stronger green band emission. Strained semiconductors offer a promising approach to fabricating multifunctional optoelectronic materials in organic electronics and biomedicine.

Synergistic Effects of Self-Doped Nanostructures as Charge Trapping Elements in Organic Field Effect Transistor Memory

Despite remarkable advances in the development of organic field-effect transistor (OFET) memories over recent years, the charge trapping elements remain confined to the critical electrets of polymers, nanoparticles, or ferroelectrics. Nevertheless, rare reports are available on the complementary advantages of different types of trapping elements integrated in one single OFET memory. To address this issue, we fabricated two kinds of pentacene-based OFET memories with solution-processed amorphous and β-phase poly(9,9-dioctylfluorene) (PFO) films as charge trapping layers, respectively. Compared to the amorphous film, the β-PFO film has self-doped nanostructures (20-120 nm) and could act as natural charge trapping elements, demonstrating the synergistic effects of combining both merits of polymer and nanoparticles into one electret. Consequently, the OFET memory with β-PFO showed nearly 26% increment in the storage capacity and a pronounced memory window of ∼45 V in 20 ms programming time. Besides, the retention time of β-PFO device extended 2 times to maintain an ON/OFF current ratio of 10(3), indicating high bias-stress reliability. Furthermore, the β-PFO device demonstrated good photosensitivity in the 430-700 nm range, which was attributed to the additive effect of smaller bandgap and self-doped nanostructures of β-phase. In this regard, the tuning of molecular conformation and aggregation in a polymer electret is an effective strategy to obtain a high performance OFET memory.