Fang-Dong Zhuang

Azaborine Compounds for Organic Field‐Effect Transistors: Efficient Synthesis, Remarkable Stability, and BN Dipole Interactions

Organic semiconductors have attracted great attention during the past few decades for the development of next-generation electronics. The incorporation of a B N unit, which is isoelectronic to the C=C moiety, into p systems provides a novel approach in the molecular engineering of organic semiconductors. BN substitution can change the electronic properties of p systems, and afford additional intermolecular dipole–dipole interactions. Therefore, BN-incorporated semiconductors provide new opportunities for organic electronics. Although significant progress has been made in azaborine chemistry, the construction of azaborine rings in large p scaffolds remains challenging. Moreover, azaborine compounds are usually susceptible to moisture and oxygen, and their thermal decomposition temperatures are around 200 8C, thus limiting their promising applications as organic materials. As a result, the charge-transport properties of azaborine compounds have rarely been investigated up to now. Only recently, Nakamura and co-workers reported a BN-fused polycyclic aromatic compound which exhibited higher intrinsic hole mobility than its carbon analog by timeresolved microwave conductivity measurements, implying that BN-substituted aromatics might outperform their carbon analogs in organic electronics. Nonetheless, electronic devices based on azaborine compounds have not yet been demonstrated. Herein, we synthesize two novel BN-substituted tetrathienonaphthalene derivatives BN-TTN-C3 and BN-TTN-C6 through an efficient one-pot electrophilic borylation method (Scheme 1). Four thiophene rings are fused onto a BNsubstituted naphthalene core to extend the p conjugated plane for intermolecular p–p stacking and charge-carrier

A straightforward strategy toward large BN-embedded π-systems: Synthesis, structure, and optoelectronic properties of extended BN heterosuperbenzenes

A straightforward strategy has been used to construct large BN-embedded π-systems simply from azaacenes. BN heterosuperbenzene derivatives, the largest BN heteroaromatics to date, have been synthesized in three steps. The molecules exhibit curved π-surfaces, showing two different conformations which are self-organized into a sandwich structure and further packed into a π-stacking column. The assembled microribbons exhibit good charge transport properties and photoconductivity, representing an important step toward the optoelectronic applications of BN-embedded aromatics.

Influence of alkyl chain length on the solid-state properties and transistor performance of BN-substituted tetrathienonaphthalenes

Flexible side chains have not drawn much attention in the development of organic semiconductors compared to the conjugated backbone counterparts. In this work, a series of BN-substituted tetrathienonaphthalenes (BN-TTNs) with methyl to hexyl side chains were synthesized to systematically investigate the influence of alkyl chain length on the solid-state properties and transistor performance. The intrinsic electronic properties of the π-conjugated backbone were not affected by different alkyl chains, but the solid-state properties, such as molecular packing structures, energy levels, thin-film morphologies, and transistor performance, were significantly influenced. Among the six compounds, BN-TTN-C3 exhibited the highest hole mobility of 0.15 cm2 V−1 s−1, whereas BN-TTN-C2 and BN-TTN-C4 did not show any field-effect mobility. This unprecedented difference of device performance was mainly caused by different thin-film morphologies. An odd–even effect of alkyl side chains on the thin-film morphology was observed for the first time, which further greatly influenced the device performance. This pronounced influence of alkyl chain length on the device performance indicates that alkyl chains play a vital role in organic electronics and should be paid more attention in future development of organic semiconductors.

Postfunctionalization of BN‐Embedded Polycyclic Aromatic Compounds for Fine‐Tuning of Their Molecular Properties

New BN-embedded, thiophene-fused, polycyclic aromatic compounds with planar geometry were designed and synthesized. The molecules showed excellent stability and chemical robustness. Postfunctionalization on this skeleton was demonstrated with a series of electrophilic bromination, palladium-catalyzed cross-coupling, and Knoevenagel condensation reactions. The π skeleton remained intact during these late-stage transformations. The optical and electronic properties have been well tuned through incorporation of electron-rich and -deficient groups on the backbone. This work shows the great advantage of the postfunctionalization strategy on BN-containing polycyclic aromatic compounds for fast diversification and materials screening.

Epindolidione-Based Conjugated Polymers: Synthesis, Electronic Structures, and Charge Transport Properties.

Development of new electron-deficient building blocks is essential to donor-acceptor conjugated polymers. Herein, epindolidione (EPD) as electron-deficient unit was integrated into conjugated polymers for the investigation of field-effect transistors for the first time. We systematically studied the electronic structures and charge transport properties of the EPD-based donor-acceptor polymers. They exhibit p-type transport characteristics with the highest mobility of up to 0.40 cm(2) V(-1) s(-1), thus demonstrating its great potential as a building block for polymer field-effect transistors and photovoltaics.

Lactone-fused electron-deficient building blocks for n-type polymer field-effect transistors: synthesis, properties, and impact of alkyl substitution positions

The development of novel electron-deficient building blocks (acceptors) plays a vital role in conjugated polymers for n-type field-effect transistors. Incorporation of lactam moieties on conjugated backbones has been one of the most important design concepts of acceptor units, whereas the potential of lactone-fused structures has seldom been explored in polymer semiconductors. Pechmann dyes are a kind of lactone-based electron-accepting units. Theoretical calculations prove that these lactone-based acceptors possess higher electron affinity than their lactam counterparts. In this work, 6,6-endo-dilactone-based Pechmann dyes were successfully incorporated into conjugated polymers for the first time, providing high electron mobilities of up to 0.51 cm2 V−1 s−1. These results demonstrated the high potential of lactone-fused structures as electron-deficient building blocks for conjugated polymers. Furthermore, different alkyl chain substitution positions were found to significantly affect the energy levels and intermolecular interactions, and consequently the device performance, indicating the important role of side chain engineering in polymer semiconductors.

Enhancing the n‐Type Conductivity and Thermoelectric Performance of Donor–Acceptor Copolymers through Donor Engineering

Conjugated polymers with high thermoelectric performance enable the fabrication of low-cost, large-area, low-toxicity, and highly flexible thermoelectric devices. However, compared to their p-type counterparts, n-type polymer thermoelectric materials show much lower performance, which is largely due to inefficient doping and a much lower conductivity. Herein, it is reported that the development of a donor-acceptor (D-A) polymer with enhanced n-doping efficiency through donor engineering of the polymer backbone. Both a high n-type electrical conductivity of 1.30 S cm-1 and an excellent power factor (PF) of 4.65 µW mK-2 are obtained, which are the highest reported values among D-A polymers. The results of multiple characterization techniques indicate that electron-withdrawing modification of the donor units enhances the electron affinity of the polymer and changes the polymer packing orientation, leading to substantially improved miscibility and n-doping efficiency. Unlike previous studies in which improving the polymer-dopant miscibility typically resulted in lower mobilities, the strategy maintains the mobility of the polymer. All these factors lead to prominent enhancement of three orders magnitude in both the electrical conductivity and the PF compared to those of the non-engineered polymer. The results demonstrate that proper donor engineering can enhance the n-doping efficiency, electrical conductivity, and thermoelectric performance of D-A copolymers.