Guobing Zhang

A bis(2-oxoindolin-3-ylidene)-benzodifuran-dione containing copolymer for high-mobility ambipolar transistors

A bis(2-oxoindolin-3-ylidene)-benzodifuran-dione (BIBDF)-based low band gap polymer (PBIBDF-BT), containing a solubilizing alkyl chain bithiophene unit as a donor, has been synthesized. The polymer with a low-lying LUMO/HOMO energy level (-4.03/-5.55 eV) exhibits efficient ambipolar charge transport. The electron and hole mobilities are as high as 1.08 and 0.30 cm(2) V(-1) s(-1), respectively.

Electrically switchable photoluminescence of fluorescent-molecule-dispersed liquid crystals prepared via photoisomerization-induced phase separation

A novel α-cyanostilbenic derivative, (Z)-2-(4-aminophenyl)-3-(4-(dodecyloxy)phenyl) acrylonitrile, is reported, wherein a Z–E isomerization process is accompanied by a remarkable decrease in compatibility with liquid crystals. Accordingly, fluorescent-molecule-dispersed liquid crystals have been prepared through a photoisomerization-induced phase separation method. The photoluminescence can be repeatedly switched by an electric field. Modulating the excitation light offers a new technique to explore electrically controllable photoluminescence.

An ABA triblock copolymer strategy for intrinsically stretchable semiconductors

A novel semiconductor–rubber–semiconductor (P3HT–PMA–P3HT) triblock copolymer has been designed and prepared according to the principle of thermoplastic elastomers. It behaves as a thermoplastic elastomer with a Youngs modulus (E) of 6 MPa for an elongation at break of 140% and exhibits good electrical properties with a carrier mobility of 9 × 10−4 cm2 V−1 s−1. This novel semiconductor may play an important role in low-cost and large-area stretchable electronics.

A luminescent liquid crystal with multistimuli tunable emission colors based on different molecular packing structures

A novel luminescent liquid crystal, (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(4-(dodecyloxy)phenyl)acrylonitrile) (PDPA), is reported, which shows green, yellow and orange colors depending on the self-assembled structure. The luminescence of PDPA can vary between those three different colors invoked by mechanical shearing and thermal annealing. Moreover, an excellent liquid crystal phase transition of PDPA is observed using polarized optical microscopy (POM) and differential scanning calorimetry (DSC) analysis. Finally, a prototype device is fabricated that demonstrates rewritable fluorescence optical recording with multistimuli luminescence tuning.

Bis(2-oxoindolin-3-ylidene)-benzodifuran-dione-based D–A polymers for high-performance n-channel transistors

Conjugated polymers based on a bis(2-oxoindolin-3-ylidene)-benzodifuran-dione (BIBDF) unit displayed promising performances for their application in organic thin-film transistors (OTFTs). Herein, three new BIBDF-based donor–acceptor (D–A) polymers, containing thieno[3,2-b]thiophene (TT), (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT) and (2-(thiophene-2-yl)alkynyl)thiophene (TAT) as donors, were synthesized and characterized. The results indicated that the donor unit plays important roles in affecting the absorption bands, HOMO levels, lamellar packing and π–π stacking distances of the BIBDF-based polymers. The OTFT devices based on the three polymers were fabricated, and their field-effect performance and environmental stability were also characterized. All three BIBDF based polymers showed good n-type field-effect characteristics. The PBIBDF-TT showed the highest electron mobility of 0.65 cm2 V−1 s−1 and the best environmental stability, while the PBIBDF-TAT showed the lowest electron mobility of 0.13 cm2 V−1 s−1. The corresponding crystalline structures and morphologies revealed that the PBIBDF-TT and PBIBDF-TVT showed close π–π distances and long-range ordered, lamellar crystalline structures both of which contributed to the high charge carrier mobility. The PBIBDF-TAT with close π–π distances but poor crystalline structures showed miserable performance. Overall, this work showed the correlation of the microstructures and properties of BIBDF-based polymers, and the field-effect performances can be effectively optimized by introducing different donor units.

A new thieno-isoindigo derivative-based D–A polymer with very low bandgap for high-performance ambipolar organic thin-film transistors

A new thieno-isoindigo derivative, bis(5-oxothieno[3,2-b]pyrrole-6-ylidene)benzodifurandione (BTPBF) was synthesized by replacing the outer benzene ring of the isoindigo derivative (BIBDF) with thiophene. This was used for the first time as an acceptor to construct a donor–acceptor polymer (PBTPBF-BT) for organic thin-film transistors. The thermal stability, photophysical-, and electrochemical properties, microstructure, and transistor characteristics were also investigated. Compared to the isoindigo derivative-based polymer PBIBDF-BT, the thieno-isoindigo derivative-based polymer PBTPBF-BT had a much smaller bandgap (0.71 eV), a similar deep LUMO level, (−3.94 eV) and a higher HOMO level (−5.18 eV). Therefore, when Au metal was used as the electrode and the devices were tested under similar vacuum conditions, PBIBDF-BT exhibited n-type transport, whereas PBTPBF-BT exhibited ambipolar transport due to the deep LUMO and suitable HOMO levels. Highest mobilities of 0.45 and 0.22 cm2 V−1 s−1 were obtained for hole and electron, respectively. Under the air condition, the hole mobility of PBTPBF-BT significantly increased to 0.61 cm2 V−1 s−1 and electron mobility was maintained at 0.07 cm2 V−1 s−1. Overall, this study demonstrates that replacing the outer benzene with thiophene can effectively vary the polymer properties such as bandgap, energy levels and, as a result, tune the transport behavior.

Highly selective and sensitive sensor based on an organic electrochemical transistor for the detection of ascorbic acid

In this study, an organic electrochemical transistor sensor (OECT) with a molecularly imprinted polymer (MIP)-modified gate electrode was prepared for the detection of ascorbic acid (AA). The combination of the amplification function of an OECT and the selective specificity of MIPs afforded a highly sensitive, selective OECT sensor. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were carried out to monitor the stepwise fabrication of the modified electrodes and the adsorption capacity of the MIP/Au electrodes. Atomic force microscopy was employed for examining the surface morphology of the electrodes. Important detection parameters, pH and detection temperature were optimized. With the change in the relative concentration of AA from 1μM to 100μM, the MIP-OECT sensor exhibited a low detection limit of 10nM (S/N > 3) and a sensitivity of 75.3μA channel current change per decade under optimal conditions. In addition, the MIP-OECT sensor exhibited excellent specific recognition ability to AA, which prevented the interference from other structurally similar compounds (e.g., aspartic acid, glucose, uric acid, glycine, glutathione, H2O2), and common metal ions (K+, Na+, Ca2+, Mg2+, and Fe2+). In addition, a series of vitamin C beverages were analyzed to demonstrate the feasibility of the MIP-OECT sensor. Using the proposed principle, several other sensors with improved performance can be constructed via the modification of organic electrochemical transistors with appropriate MIP films.

Thickness dependence of the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture

The cell gap dependence of the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture has been investigated. In this study, the morphology and electro-optical properties were analysed as a function of the thickness of the cells. The scanning electron microscopy indicates that the polymer networks become tighter with the decrease of cell gap. Increasing cell gap can improve the contrast ratio exponentially, while the threshold voltage increases linearly. The field-off response time increases, which is ascribed to the decreasing elastic force between the polymer network and the LC molecules.

Electrically switchable multi-stable cholesteric liquid crystal based on chiral ionic liquid

A multi-stable and electrically switchable cholesteric liquid crystal based on chiral ionic liquid is demonstrated. The cholesteric liquid crystal can be switched among the planar texture, focal conic texture, wide-band reflected state, and fingerprint texture by applying specific electric fields. Each of these four states exists stably for several hours without any obvious change observed at room temperature. The electro-optical properties and driving scheme of the cholesteric liquid crystal are also reported.

Bis(2-oxoindolin-3-ylidene)-benzodifuran-dione and bithiophene-based conjugated polymers for high performance ambipolar organic thin-film transistors: the impact of substitution positions on bithiophene units

Three donor–acceptor polymers based on (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo-[1,2-b:4,5-b]-difuran-2,6(3H,7H)-dione (BIBDF) and three kinds of dialkylated bithiophenes with head-to-head (HH), head-to-tail (HT), and tail-to-tail (TT) connectivity were synthesized by the Stille coupling reaction. Their photophysical and electrochemical properties, electronic device performance, and microstructure were investigated. We found that the alkyl chains substituted near the thiophene–thiophene connection cause less steric hindrance than those near the BIBDF–thiophene connection. Therefore PBIBDF-HH exhibited the preferred planarity, crystallinity, and molecular orientation, yielding the highest field-effect mobility. A maximum electron mobility of 1.23 cm2 V−1 s−1 and a maximum hole mobility of 0.37 cm2 V−1 s−1 were obtained for PBIBDF-HH-based devices. These results show that the substitution sites on the bithiophene units play an important role in the determination of molecular organization and the resulting device performance.