Indandione-Terminated Quinoids: Facile Synthesis by Alkoxide-Mediated Rearrangement Reaction and Semiconducting Properties

A series of 1,3-indandione-terminated π-conjugated quinoids were synthesized by alkoxide-mediated rearrangement reaction of the respective alkene precursors, followed by air oxidation. This new protocol allows access to quinoidal compounds with variable termini and cores. The resulting quinoids all show LUMO levels below −4.0 eV and molar extinction coefficients above 10⁵ L mol⁻¹ cm⁻¹. The optoelectronic properties of these compounds can be regulated by tuning the central cores as well as the aryl termini ascribed to the delocalized frontier molecular orbitals over the entire molecular skeleton involving aryl termini. n-Channel organic thin-film transistors with electron mobility of up to 0.38 cm² V⁻¹ s⁻¹ were fabricated, showing the potential of this new class of quinoids as organic semiconductors.     

Indandione-Terminated Quinoidal Compounds for Low-Bandgap Small Molecules with Strong Near-Infrared Absorption: Effect of Conjugation Length on the Properties

Low-bandgap organic semiconductors have attracted much attention for their multiple applications in optoelectronics. However, the realization of narrow bandgap is challenging particularly for small molecules. Herein, we have synthesized four quinoidal compounds, i. e., QSN3 , QSN4 , QSN5 and QSN6 , with electron rich S,N-heteroacene as the quinoidal core and indandione as the end-groups. The optical bandgap of the quinoidal compounds is systematically decreased with the extension of quinoidal skeleton, while maintaining stable closed-shell ground state. QSN6 absorbs an intense absorption in the first and second near-infrared region in the solid state, and has extremely low optical bandgap of 0.74 eV. Cyclic voltammetry analyses reveal that the lowest unoccupied molecular orbital (LUMO) energy levels of the four quinoidal compounds all lie below −4.1 eV, resulting in good electron-transporting characteristics in organic thin-film transistors. These results demonstrated that the combination of π-extended quinoidal core and end-groups in quinoidal compounds is an effective strategy for the synthesis of low-bandgap small molecules with good stability.     

n‐Channel Organic Transistors Processed from Halogen‐Free Solvents: Solvent Effect on Thin‐Film Morphology and Charge Transport

Non‐chlorinated solvents are highly preferable for organic electronic processing due to their environmentally friendly characteristics. Four different halogen‐free solvents, tetrafuran, toluene, meta‐xylene and 1,2,4‐trimethylbenzene, were selected to fabricate n‐channel organic thin film transistors (OTFTs) based on 3‐hexylundecyl substituted naphthalene diimides fused with (1,3‐dithiol‐2‐ylidene)malononitrile groups (NDI3HU‐DTYM2). The OTFTs based on NDI3HU‐DTYM2 showed electron mobility of up to 1.37 cm²·V^?1·s^?1 under ambient condition. This is among the highest device performance for n‐channel OTFTs processed from halogen‐free solvents. The different thin‐film morphologies, from featureless low crystalline morphology to well‐aligned nanofibres, have a great effect on the device performance. These results might shed some light on solvent selection and the resulting solution process for organic electronic devices.     

A Soluble Ladder‐Conjugated Star‐Shaped Oligomer Composed of Four Perylene Diimide Branches and a Fluorene Core: Synthesis and Properties

A new ladder‐conjugated star‐shaped oligomer electron‐transporting material TetraPDI‐PF , with four perylene diimide (PDI) branches and a fluorene core, was efficiently synthesized. The oligomer is highly soluble in dichlorobenzene with a solubility of 155 mg mL^?1, which is higher than those of PDI (35 mg mL^?1) and PDI‐Phen (70 mg mL^?1). Demonstrated by thermogravimetric analysis (TGA), the oligomer exhibits excellent thermal stability with the decomposition temperature (T_d) of 291.2 °C, which is 65 °C higher than that of PDI. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to investigate the electrochemical properties. Although the CV curves of TetraPDI‐PF are successively scanned for 15 cycles, they still remain invariable reduction potentials. The oligomer also shows outstanding photostability, even better than PDI, which maintains 99 % fluorescence intensity after irradiation for 10 min using maximum laser intensity. In the steady‐state space‐charge‐limited current (SCLC) devices, TetraPDI‐PF exhibits higher intrinsic electron mobility of 2.22×10^?5 cm² V^?1 s^?1, three orders of magnitude over that of PDI (3.52×10^?8 cm² V^?1 s^?1). The bulk heterojunction (BHJ) organic solar cells (OSCs) using TetraPDI‐PF as non‐fullerene acceptors and P3HT as donors give optimum power conversion efficiency (PCE) of 0.64 %, which is 64 times that of the PDI:P3HT BHJ cells.     

Benzimidazole Derivatives: Synthesis,Physical Properties,and n‐Type Semiconducting Properties

A series of new benzimidazole derivatives were synthesized by the solid‐state condensation and direct sublimation (SSC‐DS) method and their physical properties were investigated. The reaction yields and product stability were significantly affected by the identity of the diamine and anhydride substituents. On the other hand, the substituents of the benzimidazole ring allowed fine tuning of the emission maxima, fluorescence quantum yields, and redox potentials. The HOMO–LUMO levels were estimated by cyclic voltammetry in film on indium tin oxide (ITO) and compared with values obtained by other methods. The described benzimidazoles showed high crystallinity, which is attributed to a high planarity and interactions between carbon and heteroatoms. These compounds showed n‐type semiconducting behavior in organic field‐effect transistors (OFETs). Optimized devices for fluorinated NTCBI (naphthalene tetracarboxylic bisbenzimidazole) showed respectable electron mobilities of ～10^?2 cm² V^?1 s^?1.     

Synthesis and Elaboration of All‐cis‐1,2,4,5‐Tetrafluoro‐3‐Phenylcyclohexane: A Polar Cyclohexane Motif

A stereocontrolled synthesis of all‐cis‐1,2,4,5‐ tetrafluoro‐3‐phenylcyclohexane is developed as the first functionalised example of this polar cyclohexane motif. The dipolar nature of the ring, arising due to two 1,3‐diaxial C?F bonds, is revealed in the solid‐state (X‐ray) structure. The orthogonal conformation of the aryl and cyclohexyl rings in all‐cis‐1,2,4,5‐tetrafluoro‐3‐phenylcyclohexane, and in an ortho‐nitro derivative, result in intramolecular ^1hJ_HF and ^2hJ_CF NMR couplings relayed through hydrogen bonding. The aryl group of all‐cis‐1,2,4,5‐tetrafluoro‐3‐phenylcyclohexane is elaborated in different ways to demonstrate the versatility of this compound for delivering the motif to a range of molecular building blocks.     

Boron‐Containing Polycyclic Aromatic Hydrocarbons: Facile Synthesis of Stable,Redox‐Active Luminophores

Herein we show that replacing the two meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms transforms a near‐infrared dye into an efficient blue luminophore. This observation impressively illustrates the impact of boron doping on the frontier orbitals of PAHs. To take full advantage of this tool for the targeted design of organic electronic materials, the underlying structure–property relationships need to be further elucidated. We therefore developed a modular synthesis sequence based on a Peterson olefination, a stilbene‐type photocyclization, and an Si–B exchange reaction to substantially broaden the palette of accessible polycyclic aromatic organoboranes and to permit a direct comparison with their PAH congeners.     

Facile Synthesis of Ultrathin and Single‐Crystalline Au Nanowires

Thin is in! Recent advance in solution‐phase synthesis has led to the formation of ultrathin single‐crystalline Au nanowires with diameters of less than 10 nm. This Focus Review summarizes these syntheses and provides an exciting example of the electron transport in the ultrathin Au nanowires to demonstrate their great potential for nanoelectronic applications.

     

[4]Cyclo-N-ethyl-2,7-carbazole: Synthesis,Structural, Electronic and Charge Transport Properties

Nanorings, which are macrocycles possessing radially directed π-orbitals have shown fantastic development in the last ten years. Unravelling their unusual electronic properties has been one of the driving forces of this research field. However, and despite promising properties, their incorporation in organic electronic devices remains very scarce. In this work, we aim to contribute to bridge the gap between organic electronics and nanorings by reporting the synthesis, the structural and electronic properties and the incorporation in an organic field-effect transistor (OFET) of a cyclic tetracarbazole, namely [4]cyclo-N-ethyl-2,7-carbazole ( [4]C-Et-Cbz ). The structural, photophysical and electrochemical properties have been compared to those of structurally related analogues [4]cyclo-9,9-diethyl-2,7-fluorene [4]C-diEt-F (with carbon bridges) and [8]-cycloparaphenylene [8]CPP (without any bridge) in order to shed light on the impact of the bridging in nanorings. This work shows that nanorings can be used as an active layer in an OFET and provides a first benchmark in term of OFET characteristics for this type of molecules.     

Ferrocenylethynyl‐Terminated Azobenzenes: Synthesis,Electrochemical, and Photoisomerization Studies

Ferrocenylethynyl‐terminated derivatives 8 – 12 have been synthesized and characterized by electrochemistry and UV/Vis spectroscopy. The electrochemical and photophysical studies indicate that the electronic communication in ferrocenylethynyl‐substituted derivatives is strongly influenced by the substituted position of the ferrocenylethynyl moiety. In situ electrochemical oxidation or chemical oxidation caused a characteristically weak ligand‐to‐metal charge‐transfer (LMCT) band to appear at 700–1000 nm. Subsequent electrochemical reduction or chemical reduction recovered the most of the original curve and the color of the solution as well. Among the derivatives, compound 8 exhibits the highest cis/trans molar ratio (64:36) in the photostationary state (PSS) upon light irradiation at 365 nm. Compound 8 exhibits excellent fatigue resistance and reversibility under several repeated reversible isomerization cycles.     

FeCl3-Mediated Reaction of 1,4-Dilithio-1,3-dienes with Alkynes Affording Benzene Derivatives

Unactivated alkynes reacted with 1,4-dilithio-1,3-diene derivatives in the presence of FeCl3 affording substituted benzene derivatives via a formal[4 2] cycloaddition.     

Transition‐Metal‐Free Intramolecular Carbene Aromatic Substitution/Büchner Reaction: Synthesis of Fluorenes and [6,5,7]Benzo‐fused Rings

Intramolecular aromatic substitution and Büchner reaction have been established as powerful methods for the construction of polycyclic compounds. These reactions are traditionally catalyzed by Rh^II catalysts with α‐diazocarbonyl compounds as the substrates. Herein a transition‐metal‐free intramolecular aromatic substitution/Büchner reaction is presented. These reactions use readily available N‐tosylhydrazones as the diazo compound precursors and show wide substrate scope.     

Synthesis of a Double Helicene by a Palladium‐Catalyzed Cross‐Coupling Reaction: Structure and Physical Properties

For this study, twisted π‐extended helicene 1 and double helicene 2 with a helicene framework were synthesized through palladium‐catalyzed C?H arylation or Suzuki–Miyaura coupling reaction. X‐ray crystallography revealed grossly twisted structures that were soluble in various conventional organic solvents. Optical properties based on UV/Vis and fluorescence spectra were measured. Electrochemical properties were also studied by measurements of cyclic voltammetry in 1 and 2 , which revealed their HOMO and the LUMO energies. Theoretical calculation supports their HOMO and LUMO energies and molecular orbitals. Furthermore, a racemization process of 2 predicted that the activation free energy at 300 K would be 31.8 kcal mol^?1 by DFT calculation, which indicated the static helicity at 300 K.     

A Facile Approach to Oximes and Ethers by a Tandem NO+‐Initiated Semipinacol Rearrangement and H‐Elimination

An efficient oximation method has been developed on the basis of NO⁺‐initiated semipinacol rearrangement and subsequent proton elimination. The procedure enabled the rapid construction of a series of oximes and oxime ethers with spiro quaternary stereocenters from allylic silyl ethers. Additional features of this reaction include wide substrate tolerance as well as the commercial availability of the safe nitrosation reagent NOBF₄. The key N‐heterotricyclic cores of three natural alkaloids, tuberostemoninol B, (+)‐quebrachidine, and an insecticide, were also constructed efficiently by this method.