Naphthalenediimide-Benzothiadiazole Copolymer Semiconductors: Rational Molecular Design for Air-Stable Ambipolar Charge Transport

Rational design of air-stable ambipolar polymeric semiconductors was achieved by covalently connecting naphthalenediimide (NDI) units with benzothiadiazole (BZ) through thiophene (T) linkers, namely, <b>PNDI-</b><i><b>mT</b></i><b>(BZ)</b><i><b>mT</b></i> (<i>m</i> = 1, 2), in which well-coplanar <i><b>mT</b></i><b>(BZ)</b><i><b>mT</b></i> moieties as a whole act as donors rather than acceptors reported in previous studies. Decreasing the number of thiophene linkers from <i>m</i> = 2 to 1 lowers both LUMO and HOMO energy levels. As a result, the carriers in organic thin film transistors (OTFTs) could be switched from unipolar <i>p</i>-channel only to ambipolar transport. In ambient conditions, <b>PNDI-</b><i><b>2T</b></i><b>(BZ)</b><i><b>2T</b></i> presents an average hole mobility of 0.07 ± 0.02 cm² V^–1 s^–1, while <b>PNDI-</b><i><b>T</b></i><b>(BZ)</b><i><b>T</b></i> exhibits balanced ambipolar charge transport in a bottom-gate/top-contact device architecture, the average electron and hole mobilities was 0.05 ± 0.02 (<i>μ</i>_e) and 0.1 ± 0.03 (<i>μ</i>_h) cm² V^–1 s^–1, respectively. Moreover, OTFTs based on both polymer show good air-stability with negligible changes after stored in ambient over 3 months

Solvatomechanical Bending of Organic Charge Transfer Cocrystal

We report here a new ternary solvated (perylene-TCNB)·2THF cocrystal, which can transform into binary perylene-TCNB cocrystal reversibly by successive desorption or absorption of THF solvent. As a consequence, macroscopic mechanical bending would be realized when repeated stimulation with THF solvent. The present results clearly demonstrated that solvent induced mechanical bending is driven by structural change at the molecular scale. Such solvatomechanical bending behavior is clearly revealed for the first time

Solvatomechanical Bending of Organic Charge Transfer Cocrystal

We report here a new ternary solvated (perylene-TCNB)·2THF cocrystal, which can transform into binary perylene-TCNB cocrystal reversibly by successive desorption or absorption of THF solvent. As a consequence, macroscopic mechanical bending would be realized when repeated stimulation with THF solvent. The present results clearly demonstrated that solvent induced mechanical bending is driven by structural change at the molecular scale. Such solvatomechanical bending behavior is clearly revealed for the first time

Substrate Effects in the Supramolecular Self-Assembly of 2,4,6-Tris(4-bromophenyl)-1,3,5-triazine on Graphite and Graphene

Two-dimensional self-assembly of star-shaped 2,4,6-tris­(4-bromophenyl)-1,3,5-triazine (BPT) molecule is investigated both on highly oriented pyrolytic graphite (HOPG) and single-layer graphene (SLG) grown on a polycrystalline Cu foil. Scanning tunneling microscopy (STM) reveals that this molecule can form different self-assembling structures on these two different surfaces. On the basis of high-resolution STM images, we find that BPT molecules can form compact and loose assembly patterns with different packing densities on HOPG surface and a porous structure with hexagonal-like cavities on SLG surface. A combination of STM and density functional theory calculations elucidates the interplay of molecule–molecule and molecule–substrate interactions on the assembling behavior on both substrates

Solvatomechanical Bending of Organic Charge Transfer Cocrystal

We report here a new ternary solvated (perylene-TCNB)·2THF cocrystal, which can transform into binary perylene-TCNB cocrystal reversibly by successive desorption or absorption of THF solvent. As a consequence, macroscopic mechanical bending would be realized when repeated stimulation with THF solvent. The present results clearly demonstrated that solvent induced mechanical bending is driven by structural change at the molecular scale. Such solvatomechanical bending behavior is clearly revealed for the first time

Synthesis of a Conjugated Polymer with Broad Absorption and Its Application in High-Performance Phototransistors

An amorphous copolymer (PBDT–BBT) of 4,8-bis­(2-thienyl)­benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene and 5,5′-bibenzo­[<i>c</i>]­[1,2,5]­thiadiazole was synthesized by Stille coupling polymerization. PBDT–BBT exhibited good solution processability, excellent thermal stability with decomposition temperature of 437 °C, broad absorption (300–800 nm), deep HOMO level (−5.7 eV), and LUMO level (−3.7 eV). The microstructure order of PBDT–BBT thin films is not susceptible to thermal annealing temperature (80–200 °C). Field-effect transistors based on this polymer exhibited a charge-carrier mobility of 6 × 10^–3 cm² V^–1 s^–1, threshold voltage of −1 V, and on/off current ratio of 10⁶ without any post-treatments. Thin film phototransistors of PBDT–BBT exhibited a photoresponsivity of 3200 mA W^–1 and photocurrent/dark current ratio of 4 × 10⁵

Critical Content of Ultrahigh-Molecular-Weight Polyethylene To Induce the Highest Nucleation Rate for Isotactic Polypropylene in Blends

The influence of the addition of low amounts of ultrahigh-molecular-weight polyethylene (UHMWPE) on the crystallization kinetics of isotactic polypropylene (iPP) in iPP/UHMWPE blends has been investigated by means of differential scanning calorimetry (DSC) and polarized optical microscopy. During the nonisothermal crystallization process, the primarily formed UHMWPE crystals serve as heterogeneous nucleating agents for iPP nucleation, whereas during the isothermal crystallization process, UHMWPE is in the molten state, iPP nucleation preferentially occurs at the UHMWPE and iPP phase interfaces, and the spherulitic growth rates are not obviously affected. It is particularly interesting to find a critical UHMWPE content (2.5 wt %) in the blends to induce the highest iPP nucleation rate; however, above the critical UHMWPE content, the iPP nucleation rate slows because of aggregation of the UHMWPE component. A delicately designed DSC measurement provides insight into the nucleation mechanism of iPP at the interfaces between the UHMWPE and iPP phase domains. It is proposed that the concentration fluctuations generated from the unstable inhomogeneous phase interfaces in the iPP/UHMWPE blends promote the formation of nuclei, which eventually enhances the nucleation and overall crystallization rates of the iPP component

Solution-Processed Flexible Organic Ferroelectric Phototransistor

In this article, we demonstrate ferroelectric insulator, P­(VDF-TrFE), can be integrated with red light sensitive polymeric semiconductor, P­(DPP-TzBT), toward ferroelectric organic phototransistors (OPTs). This ferroelectricity-modulated phototransistor possesses different nonvolatile and tunable dark current states due to P­(VDF-TrFE)’s remnant polarization. As a result, the OPT is endowed with a tunable dark current level ranging from 1 nA to 100 nA. Once the OPT is programmed or electrically polarized, its photo-to-dark (signal-to-noise) ratio can be “flexible” during photodetection process, without gate bias application. This kind of organic ferroelectric phototransistor has great potential in detecting wide ranges of light signals with good linearity. Moreover, its tuning mechanism discussed in this work can be helpful to understand the operation mechanism of organic phototransistor (OPT). It can be promising for novel photodetection application in plastic electronic devices

Graphene Oxide as a Monoatomic Blocking Layer

Monolayer graphene oxide (mGO) is shown to effectively protect molecular thin films from reorganization and function as an atomically thin barrier for vapor-deposited Ti/Al metal top electrodes. Fragile organic Langmuir–Blodgett (LB) films of C₂₂ fatty acid cadmium salts (cadmium(II) behenate) were covered by a compressed mosaic LB film of mGO flakes. These hybrid LB films were examined with atomic force microscopy (AFM) and X-ray reflectivity, both with and without the metal top electrodes. While the AFM enabled surface and morphology analysis, the X-ray reflectivity allowed for a detailed structural depth profiling of the organic film and mGO layer below the metal top layers. The structure of the mGO-protected LB films was found to be perfectly preserved; in contrast, it has previously been shown that metal deposition completely destroys the first two LB layers of unprotected films. This study provides clear evidence of the efficient protection offered by a single atomic layer of GO

Unveiling Secrets of Overcoming the “Heteroatom Problem” in Palladium-Catalyzed Aerobic C–H Functionalization of Heterocycles: A DFT Mechanistic Study

Directed C–H functionalization of heterocycles through an exocyclic directing group (DG) is challenging due to the interference of the endocyclic heteroatom(s). Recently, the “heteroatom problem” was circumvented with the development of the protection-free Pd-catalyzed aerobic C–H functionalization of heterocycles guided by an exocyclic CONHOMe DG. We herein provide DFT mechanistic insights to facilitate the expansion of the strategy. The transformation proceeds as follows. First, the Pd₂(dba)₃ precursor interacts with <i>t</i>-BuNC (L, one of the substrates) and O₂ to form the L₂Pd­(II)-η²-O₂ peroxopalladium­(II) species that can selectively oxidize <i>N</i>-methoxy amide (e.g., PyCONHOMe) substrate, giving an active L₂Pd­(II)­X₂ (X = PyCONOMe) species and releasing H₂O₂. After <i>t</i>-BuNC ligand migratory insertion followed by a 1,3-acyl migration and association with another <i>t</i>-BuNC, L₂Pd­(II)­X₂ converts to a more stable C-amidinyl L₂Pd­(II)­XX′ (X′ = PyCON­(<i>t</i>-Bu)­CNOMe) species. Finally, L₂Pd­(II)­XX′ undergoes C–H activation and C–C reductive elimination, affording the product. The C–H activation is the rate-determining step. The success of the strategy has three origins: (i) the <i>N</i>-methoxy amide DG can be easily oxidized <i>in situ</i> to generate the active L₂Pd­(II)­X₂ species via the oxidase pathway, thus preventing the destructive oxygenase pathway leading to stable <i>t</i>-BuNCO or the O-bridged dimeric Pd­(II) species. The methoxy group in this amide DG greatly facilitates the oxidase pathway, and the tautomerization of <i>N</i>-methoxy amide to its imidic acid tautomer makes the oxidation of the substrate even easier. (ii) The X group in L₂Pd­(II)­X₂ can serve as an internal base to promote the C–H activation via CMD (concerted metalation-deprotonation) mechanism. (iii) The strong coordination ability of <i>t</i>-BuNC substrate/ligand suppresses the conventional cyclopalladation pathway enabled by the coordination of an endocyclic heteroatom to the Pd-center