Yunke Qin

One-pot synthesis of core-expanded naphthalene diimides: enabling N-substituent modulation for diverse n-type organic materials.

A mild and versatile one-pot synthesis of core-expanded naphthalene diimides has been developed, which undergoes a nucleophilic aromatic substitution reaction and then an imidization reaction, allowing an easy and low-cost access to diverse n-type organic materials. Some newly synthesized compounds by this one-pot operation exhibited high electron mobility of up to 0.70 cm(2) V(-1) s(-1) in ambient conditions.

Charge-Transfer Complex Crystal Based on Extended-π-Conjugated Acceptor and Sulfur-Bridged Annulene: Charge-Transfer Interaction and Remarkable High Ambipolar Transport Characteristics

A single crystal of a novel mixed-stack donor-acceptor complex formed by a tetracyanoquinodimethane derivative with an extended π-conjugated system and a sulfur-bridged annulene displays the highest ambipolar transport behavior among donor-acceptor complexes reported with electron and hole mobilities reaching up to 0.24 and 0.77 cm(2) V(-1) s(-1) , respectively.

Thiophene-Diketopyrrolopyrrole-Based Quinoidal Small Molecules as Solution-Processable and Air-Stable Organic Semiconductors: Tuning of the Length and Branching Position of the Alkyl Side Chain toward a High-Performance n-Channel Organic Field-Effect Transistor

A series of thiophene-diketopyrrolopyrrole-based quinoidal small molecules (TDPPQ-2-TDPPQ-5) bearing branched alkyl chains with different side-chain lengths and varied branching positions are synthesized. Field-effect transistor (FET) measurement combined with thin-film characterization is utilized to systematically probe the influence of the side-chain length and branching position on the film microstructure, molecular packing, and, hence, charge-transport property. All of these TDPPQ derivatives show air-stable n-channel transporting behavior in spin-coated FET devices, which exhibit no significant decrease in mobility even after being stored in air for 2 months. Most notably, TDPPQ-3 exhibits an outstanding n-channel semiconducting property with electron mobilities up to 0.72 cm(2) V(-1) s(-1), which is an unprecedented value for spin-coated DPP-based n-type semiconducting small molecules. A balance of high crystallinity, satisfactory thickness uniformity and continuity, and strong intermolecular interaction accounts for the superior charge-transport characteristics of TDPPQ-3 films. Our study demonstrates that tuning the length and branching position of alkyl side chains of semiconducting molecules is a powerful strategy for achieving high FET performance.

Ambipolar organic field-effect transistors based on diketopyrrolopyrrole derivatives containing different π-conjugating spacers

We report the synthesis and characterization of two new DPP-based small molecules, BTDPPCN and TTDPPCN. By variation of π-conjugating spacers from bithiophene to thieno[3,2-b]thiophene, a lower LUMO level is obtained for TTDPPCN, but both compounds have a similar band gap of about 1.6 eV. Under ambient conditions, the excellent ambipolarity of BTDPPCN is demonstrated by balanced charge carrier mobilities of 0.065 and 0.031 cm2 V−1 s−1 for n- and p-channels after thermal annealing. The FETs based on TTDPPCN films also showed ambipolar charge transport properties with a very high electron mobility of 0.80 cm2 V−1 s−1 upon thermal annealing at 90 °C and a hole mobility of 0.024 cm2 V−1 s−1 at 150 °C.

Thieno[3,2‐b]thiophene‐Diketopyrrolopyrrole‐Based Quinoidal Small Molecules: Synthesis, Characterization, Redox Behavior, and n‐Channel Organic Field‐Effect Transistors

We report the synthesis, characterization, redox behavior, and n-channel organic field-effect (OFET) characteristics of a new class of thieno[3,2-b]thiophene-diketopyrrolopyrrole-based quinoidal small molecules 3 and 4. Under ambient atmosphere, solution-processed thin-film transistors based on 3 and 4 exhibit maximum electron mobilities up to 0.22 and 0.16 cm(2) V(-1) s(-1) , respectively, with on-off current ratios (Ion /Ioff ) of more than than 10(6) . Cyclic voltammetry analysis showed that this class of quinoidal derivatives exhibited excellent reversible two-stage reduction behavior. This property was further investigated by a stepwise reductive titration of 4, in which sequential reduction to the radical anion and then the dianion were observed.

Enhancement of the p-channel performance of sulfur-bridged annulene through a donor–acceptor co-crystal approach

By introducing naphthalene diimide into the meso-diphenyl tetrathia[22]annulene[2,1,2,1], a natural donor–acceptor co-crystal was prepared. In this co-crystal, donor and acceptor alternatingly stack into one-dimensional columns along the π–π stacking direction. With π–π interaction among the donor molecules, no effective π–π overlapping between DPNDIs in the acceptor columns was observed. Microcrystal transistor devices based on this D–A co-crystal displayed higher hole transport performance compared to the pristine crystals of donor molecules. Quantum calculation confirmed the absence of electron transport pathways and the super exchange between the adjacent donor and acceptor. From the diversity and versatility of the donor and acceptor used, we believe that the strategy developed here would be readily employed to tune the charge transport of organic semiconductors.

Optimization of the thermoelectric properties of poly(nickel-ethylenetetrathiolate) synthesized via potentiostatic deposition

The coordination polymer poly(nickel-ethylenetetrathiolate) (poly(Ni-ett)), formed by nickel(II) and 1,1,2,2-ethenetetrathiolate (ett), is the most promising N-type organic thermoelectric material ever reported; it is synthesized via potentiostatic deposition, and the effect of different applied potentials on the optimal performance of the polymers is investigated. The optimal thermoelectric property of poly(Ni-ett) synthesized at 0.6 V is remarkably greater than that of the polymers synthesized at 1 and 1.6 V, exhibiting a maximum power factor of up to 131.6 μW/mK2 at 360 K. Furthermore, the structure-property correlation of poly(Ni-ett) is also extensively investigated. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the larger size of crystalline domains and the higher oxidation state of poly(Ni-ett) synthesized at 0.6 V possibly results in the higher bulk mobility and carrier concentration in the polymer chains, respectively, accounting for the enhanced power factor.

π-Conjugated dithieno[3,2-b:2′,3′-d]pyrrole (DTP) oligomers for organic thin-film transistors

Two new molecules with acceptor–donor–donor–acceptor (A–D–D–A) configuration bearing coplanar electron-donating dithieno[3,2-b:2′,3′-d]pyrrole (DTP) as the donor unit and the electron-withdrawing dicyanovinylene as the acceptor block, DTP-L and DTP-S, were synthesized. The introduction of two branched alkyl chains with different lengths at the N-position of DTP led to different transport properties with the longer alkyl chains (DTP-L) showing hole mobility of up to 0.12 cm2 V−1 s−1 with on/off ratios of 106 without being subjected to annealing, and the one with short alkyl chains (DTP-S) exhibiting very poor hole mobility of 7.0 × 10−4 cm2 V−1 s−1. The poor performance of DTP-S films was mainly caused by a less ordered film and low crystallinity.

Two soluble polymers with lower ionization potentials: doping and thermoelectric properties

Doping and thermoelectric properties of two solution-processable conjugated polymers with low ionization potentials (IPs) have been studied and compared. An optimized thermoelectric power factor (PF) approaching 40 μW m−1 K−2 at 390 K was achieved in films of polymer PDTPT-C12, by performing doping treatment with LiTFSI solution in air, while an optimized thermoelectric power factor around 12 μW m−1 K−2 at 390 K was observed when CuTFSI2 solution was used instead of LiTFSI. In contrast, such effects on thermoelectric performance as a result of dopant species were not observed in the other studied polymer PTVT2T-C12 with comparable IP. Based on the results of thermoelectric measurements and optical spectroscopy as well as photoelectron spectroscopy, the role of Li+ in the resultant thermoelectric performance was proposed. Moreover, owing to the relatively low IPs of the two studied polymers, the as-doped polymer films are reasonably stable under ambient conditions. Therefore, N-alkyl dithieno[3,2b:2′,3′-d] pyrroles (DTPs) as exemplified in the case of PDTPT-C12 are suggested to be promising building-blocks and the incorporation of small cations like Li+ may be an alternative to increase the thermopower in solid state devices.

Sulphur bridged [22]annulene[2.1.2.1] based organic field-effect transistors: interplay of the steric bulk and charge transport

New, neutral, slightly puckered aromatic meso-substituted tetrathia[22]porphyrin[2.1.2.1] (TTP) macrocyclic architectures display structure dependent p-type semiconductor behaviour and constitute molecular field effect transistors with a high on/off ratio (1 × 106) and high mobility (0.32 cm2 V−1 s−1) in thin films deposited on octadecyltrichlorosilane (OTS) modified SiO2. In order to study the influence of steric bulk, molecules with an increasing steric bulk at the meso-position have been synthesized and studied both experimentally and theoretically. The charge transport behavior was evaluated from their thin film organic field-effect transistor (OFET) devices. Single crystal analysis and thin film morphologies of the molecules showed that incorporating a branched hydrocarbon group at the meso-phenyl substituents of TTP not only alters face to face stacking patterns but also changes the morphology of the thin films from highly crystalline to amorphous, as well as lowering the solubility in organic solvents. Such features lead to deterioration of the performance of the organic semiconductor (OSC) devices.