Danqing Liu

The Position of Nitrogen in N‐Heteropentacenes Matters

An exploratory study on novel silylethynylated N-heteropentacenes, which have their N atoms on the terminal rings of the pentacene backbone, is reported. This study leads to both p- and n-channel organic thin-film transistors with high field-effect mobility and also reveals that the position of the N atoms plays an important role in tuning the structures and properties of organic semiconductors based on N-heteropentacenes.

Self-Assembled Monolayers of Phosphonic Acids with Enhanced Surface Energy for High-Performance Solution-Processed N-Channel Organic Thin-Film Transistors†

A self-assembled monolayer (SAM) is only a few nanometers thick, but can dramatically change the surface properties. Herein we report novel SAMs of phosphonic acids (shown in Figure 1a), which are completely wettable by various organic solvents because of the enhanced surface energy of the SAMs, leading to solution-processed n-channel organic thin-film transistors (OTFTs) with average field effect mobility as high as 1.6 cmV 1 s . OTFTs are elemental units in organic integrated circuits that, for example, operate radio-frequency identification (RFID) tags and sensors and are used to drive individual pixels in active matrix displays. For these applications, solution-processed OTFTs can be fabricated onto flexible substrates over a large area at low cost using rollto-roll or ink-jet printing techniques. OTFTs are interface devices with their performance highly dependent on the interface between organic semiconductors and gate dielectrics no matter whether the organic semiconductors are processed by vacuum deposition or solution-based methods. Owing to the key importance of the semiconductor–dielectric interface, great efforts have been made in interface engineering to control the interface structures, such as molecular ordering, surface dipoles, and film morphology. By virtue of their ability to manipulating the surface properties, SAMs of organosilanes and phosphonic acids have been developed as a very powerful tool to modify the dielectric oxide surface in OTFTs, particularly vacuum-deposited OTFTs. It is worth noting that the success of a specific SAM in vacuumdeposited OTFTs is often barely duplicated in solutionprocessed OTFTs, and controlling the morphology of solution-processed films of organic semiconductors is usually complex. One key factor that affects the nucleation and

Hydrogen-Bonded Dihydrotetraazapentacenes

Three new members of N-heteropentacenes explored herein have adjacent pyrazine and dihydropyrazine rings at one end of the pentacene backbone. Interesting findings from this study include self-complementary N-H···N H-bonds in the solid state, solvent-dependent UV-vis absorption caused by H-bonding, and new p-type organic semiconductors with field effect mobility up to 0.7 cm(2) V(-1) s(-1).

Self‐Assembled Monolayers of Cyclohexyl‐Terminated Phosphonic Acids as a General Dielectric Surface for High‐Performance Organic Thin‐Film Transistors

A novel self-assembled monolayer (SAM) on AlOy /TiOx is terminated with cyclohexyl groups, an unprecedented terminal group for all kinds of SAMs. The SAM-modified AlOy /TiOx functions as a general dielectric, enabling organic thin-film transistors with a field-effect mobility higher than 5 cm(2) V(-1) s(-1) for both holes and electrons, good air stability with low operating voltage, and general applicability to solution-processed and vacuum-deposited n-type and p-type organic semiconductors.

Highly electron-deficient hexaazapentacenes and their dihydro precursors.

Novel silylethynylated N-heteropentacenes that have three adjacent pyrazine rings at the center of a pentacene backbone are reported. These hexaazapentacenes exhibit a record low energy level of lowest unoccupied molecular orbital (LUMO) for N-heteropentacenes and thus are able to oxidize dihydroanthracene to anthracene. Their synthetic precursors are the corresponding dihydrohexaazapentacenes, which exhibit interesting H-bonding.

The application of a high-k polymer in flexible low-voltage organic thin-film transistors

Although much progress has been made in the study of high-mobility organic semiconductors in recent years, one major challenge for organic thin film transistors (OTFTs) in real applications is the relatively high operating voltage, which is mainly related to the gate dielectric of the OTFT. Here we show the application of a high-k poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) (P(VDF-TrFE-CFE)) as the gate dielectric of flexible low-voltage pentacene OTFTs for the first time. The performance of the OTFTs is optimized by modifying the surface of P(VDF-TrFE-CFE) films with various thin polymer films by a solution process. The flexible OTFTs show excellent performance at the operating voltage of 4 V and good stability after 1000 bending tests. It is expected that P(VDF-TrFE-CFE) is a suitable gate dielectric for low-voltage OTFTs based on various small-molecule organic semiconductors because P(VDF-TrFE-CFE) terpolymer films can be easily modified with different thin polymer films by a solution process.

Heptagon-Embedded Pentacene: Synthesis, Structures, and Thin-Film Transistors of Dibenzo[d,d′]benzo[1,2-a:4,5-a′]dicycloheptenes†

This study presents a new class of conjugated polycyclic molecules that contain seven-membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C6-C7-C6-C7-C6 polycyclic framework with a p-quinodimethane core. With field-effect mobilities of up to 0.76 cm(2) V(-1) s(-1) as measured from solution-processed thin-film transistors, these molecules are alternatives to the well-studied pentacene analogues for applications in organic electronic devices.

Monolayer Field‐Effect Transistors of Nonplanar Organic Semiconductors with Brickwork Arrangement

DOI: 10.1002/adma.201500149 Orange solutions of 2a-d exhibited almost identical UV–vis absorption with the longest-wavelength absorption maximum at 512 nm as shown in Figure 2 . To determine the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the redox behaviors of 2a-d in solution were investigated with cyclic voltammetry. The cyclic voltammograms of 2a-d (Figure S2, Supporting Information) are essentially the same exhibiting one reversible reduction peak ca. −1.90 V and two quasi-reversible oxidation peaks at ca. 0.20 and 0.50 V versus ferrocenium/ferrocene. From these potentials, the HOMO and LUMO energy levels of 2a-d are estimated as −5.3 and −3.2 eV, respectively, [ 6 ]

Induced crystallization of rubrene with diazapentacene as the template

The poor crystallinity of rubrene in conventional films is a well-known obstacle limiting practical applications of rubrene in thin film transistors. Here we report a study on using 6,13-diazapentacene (DAP) as a template to induce crystallization of rubrene in thin film transistors. This study demonstrates that DAP is a suitable template molecule with negligible contribution to the conduction channel and leads to polycrystalline thin films of rubrene with field effect mobility as high as 0.68 cm2 V−1 s−1. This induced-crystallization strategy highly depends on a unique octadecylphosphonic acid (ODPA) bilayer-step surface, which is found to play important roles in controlling the growth of both DAP and rubrene.

Vapochromic and semiconducting solids of a bifunctional hydrocarbon

This study explores a bifunctional hydrocarbon, which has two non-planar dibenzocycloheptatriene moieties linked by three cumulative C–C double bonds. This flexible conjugated molecule can adopt two conformations, namely, syn and anti, in its crystals. Of particular interest is that the molecule’s solids not only function as p-type semiconductors with field effect mobility of 0.02 cm2 V−1 S−1 but also exhibit vapochromic behavior with high selectivity. Upon selectively trapping specific volatile molecules, such as toluene and m-xylene, in the crystal lattice, the guest-free crystals of the syn conformer change to the clathrate crystals of the anti conformer accompanied by a change of color from red to orange. The unique combination of the two useful functions of this molecule can be attributed to its cycloheptatriene and cumulene moieties, both of which have rarely been used in building blocks for organic functional materials.