Enhanced Performance of Benzothieno[3,2‐b]thiophene (BTT)‐Based Bottom‐Contact Thin‐Film Transistors

Three new benzothieno[3,2‐b]thiophene ( BTT ; 1 ) derivatives, which were end‐functionalized with phenyl ( BTT‐P ; 2 ), benzothiophenyl ( BTT‐BT ; 3 ), and benzothieno[3,2‐b]thiophenyl groups ( BBTT ; 4 ; dimer of 1 ), were synthesized and characterized in organic thin‐film transistors (OTFTs). A new and improved synthetic method for BTT s was developed, which enabled the efficient realization of new BTT ‐based semiconductors. The crystal structure of BBTT was determined by single‐crystal X‐ray diffraction. Within this family, BBTT , which had the largest conjugation of the BTT derivatives in this study, exhibited the highest p‐channel characteristic, with a carrier mobility as high as 0.22 cm² V^?1 s^?1 and a current on/off ratio of 1×10⁷, as well as good ambient stability for bottom‐contact/bottom‐gate OTFT devices. The device characteristics were correlated with the film morphologies and microstructures of the corresponding compounds.     

The Origin of the Room‐Temperature Stability of [TTF].+⋅⋅⋅[TTF].+ Long,Multicenter Bonds Found in Functionalized π‐[R‐TTF]22+ Dimers Included in the Cucurbit[8]uril Cavity

A computational study is performed to identify the origin of the room‐temperature stability, in aqueous solution, of functionalized π‐[R‐TTF]₂²⁺ dimers (TTF=tetrathiafulvalene; R=(CH₂OCH₂)₅CH₂OH) included in the cavity of a cucurbit[8]uril (CB[8]) molecule. π‐[R‐TTF]₂²⁺ dimers in pure water are weakly stable, and are mostly dissociated at room temperature. Upon addition of CB[8] to an aqueous π‐[R‐TTF]₂²⁺ solution, a (π‐[R‐TTF]₂?CB[8])²⁺ inclusion complex is formed. The same complex is obtained after the sequential inclusion of two [R‐TTF]^.+ monomers in the CB[8] molecule. Both processes are thermodynamically and kinetically allowed. π‐[R‐TTF]₂²⁺ dimers dissolved in pure water present a [TTF]^.+???[TTF]^.+ long, multicenter bond, similar to that already identified in π‐[TTF]₂²⁺ dimers dissolved in organic solvents. Upon their inclusion in CB[8], the strength and other features of the [TTF]^.+???[TTF]^.+ long, multicenter bond are preserved. The room temperature stability of the π‐[R‐TTF]₂²⁺ dimers included in CB[8] is shown to originate in the π‐[R‐TTF]₂²⁺???CB[8] interaction, the strength of which comes from a strongly attractive electrostatic component and a dispersion component. Such a dominant electrostatic term is caused by the strongly polarized charge distribution in CB[8], the geometrical complementarity of the π‐[R‐TTF]₂²⁺ and CB[8] geometries, and the amplifying effect of the 2+ charge in π‐[R‐TTF]₂²⁺.     

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 cm² 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.     

An A‐D‐A′‐D‐A Conjugated Molecule Entailing Diazapentalene Unit for an n‐Type Organic Semiconductor

Conjugated molecules with low lying LUMO levels are demanding for the development of air stable n‐type organic semiconductors. In this paper, we report a new A‐D‐A′‐D‐A conjugated molecule ( DAPDCV ) entailing diazapentalene (DAP) and dicyanovinylene groups as electron accepting units. Both theoretical and electrochemical studies manifest that the incorporation of DAP unit in the conjugated molecule can effectively lower the LUMO energy level. Accordingly, thin film of DAPDCV shows n‐type semiconducting behavior with electron mobility up to 0.16 cm²?V^?1?s^?1 after thermal annealing under N₂ atmosphere. Moreover, thin film of DAPDCV also shows stable n‐type transporting property in air with mobility reaching 0.078 cm²?V^?1?s^?1.     

Thienoacene‐Fused Pentalenes: Syntheses,Structures, Physical Properties and Applications for Organic Field‐Effect Transistors

Three soluble and stable thienoacene‐fused pentalene derivatives ( 1 – 3 ) with different π‐conjugation lengths were synthesized. X‐ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field‐effect transistors (OFETs) were also investigated. The highest field‐effect hole mobility of 0.016, 0.036 and 0.001 cm² V^?1 s^?1 was achieved for solution‐processed thin films of 1 – 3 , respectively.     

A Compact Tetrathiafulvalene–Benzothiadiazole Dyad and Its Highly Symmetrical Charge‐Transfer Salt: Ordered Donor π‐Stacks Closely Bound to Their Acceptors

A compact and planar donor–acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) units has been synthesised and experimentally characterised by structural, optical, and electrochemical methods. Solution‐processed and thermally evaporated thin films of 1 have also been explored as active materials in organic field‐effect transistors (OFETs). For these devices, hole field‐effect mobilities of μ_FE=(1.3±0.5)×10^?3 and (2.7±0.4)×10^?3 cm² V s^?1 were determined for the solution‐processed and thermally evaporated thin films, respectively. An intense intramolecular charge‐transfer (ICT) transition at around 495 nm dominates the optical absorption spectrum of the neutral dyad, which also shows a weak emission from its ICT state. The iodine‐induced oxidation of 1 leads to a partially oxidised crystalline charge‐transfer (CT) salt {( 1 )₂I₃}, and eventually also to a fully oxidised compound { 1 I₃} ? 1/2I₂. Single crystals of the former CT compound, exhibiting a highly symmetrical crystal structure, reveal a fairly good room temperature electrical conductivity of the order of 2 S cm^?1. The one‐dimensional spin system bears compactly bonded BTD acceptors (spatial localisation of the LUMO) along its ridge.     

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.     

Tetrathiafulvalene‐Based Mixed‐Valence Acceptor–Donor–Acceptor Triads: A Joint Theoretical and Experimental Approach

This work presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)‐based acceptor–donor–acceptor triads (BQ–TTF–BQ and BTCNQ–TTF—BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano‐p‐quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum‐chemical calculations. Emphasis is placed on the mixed‐valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ–TTF–BQ and BTCNQ–TTF–BTCNQ triads in their radical anion states behave as class‐II mixed‐valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc‐pVTZ), taking into account the solvent effects, predict charge‐localised species (BQ ^{. ?}–TTF–BQ and BTCNQ ^{. ?}–TTF–BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ–TTF–BTCNQ anion, in accordance with the more electron‐withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low‐energy, broad absorption bands observed experimentally for the BQ–TTF–BQ and BTCNQ–TTF–BTCNQ radical anions are associated with the intervalence charge transfer (IV‐CT) electronic transition and two nearby donor‐to‐acceptor CT excitations. The study highlights the molecular efficiency of the electron‐donor TTF unit as a molecular wire connecting two acceptor redox centres.     

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp2‐Hybridized Graphitic Polymer

Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three‐dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three‐dimensional organic polymers is challenging. Now, the synthesis of a three‐dimensional π‐conjugated porous organic polymer (3D p‐POP) using catalyst‐free Diels–Alder cycloaddition polymerization followed by acid‐promoted aromatization is presented. With a surface area of 801 m² g^?1, full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10^?4 S cm^?1 upon treatment with I₂ vapor, the 3D p‐POP is the first member of a new class of permanently porous 3D organic semiconductors.     

Kinetics of the reactions of OH radicals with 2‐methoxy‐6‐(trifluoromethyl)pyridine,diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol at 298 ± 2 K

Rate constants for the reactions of 2‐methoxy‐6‐(trifluoromethyl)pyridine, diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with OH radicals have been measured at 298 ± 2 K using a relative rate method. The measured rate constants (cm³ molecule^?1 s^?1) are (1.54 ± 0.21) × 10^?12 for 2‐methoxy‐6‐(trifluoromethyl)pyridine, (1.19 ± 0.25) × 10^?10 for diethylamine, and (1.76 ± 0.38) × 10^?12 for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol, where the indicated errors are the estimated overall uncertainties including those in the rate constants for the reference compounds. No reaction of 2‐methoxy‐6‐(trifluoromethyl)pyridine with gaseous nitric acid was observed, and an upper limit to the rate constant for the reaction of 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with O₃ of <7 × 10^{? 20} cm³ molecule^?1 s^?1 was determined. Using a 12‐h average daytime OH radical concentration of 2 × 10⁶ molecule cm^?3, the lifetimes of the volatile organic compounds studied here with respect to reaction with OH radicals are 7.5 days for 2‐methoxy‐6‐(trifluoromethyl)pyridine, 1.2 h for diethylamine, and 6.6 days for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol. Likely reaction mechanisms are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 631–638, 2011     

Incorporation of 2,6‐Connected Azulene Units into the Backbone of Conjugated Polymers: Towards High‐Performance Organic Optoelectronic Materials

Azulene is a promising candidate for constructing optoelectronic materials. An effective strategy is presented to obtain high‐performance conjugated polymers by incorporating 2,6‐connected azulene units into the polymeric backbone, and two conjugated copolymers P(TBAzDI‐TPD) and P(TBAzDI‐TFB) were designed and synthesized based on this strategy. They are the first two examples for 2,6‐connected azulene‐based conjugated polymers and exhibit unipolar n‐type transistor performance with an electron mobility of up to 0.42 cm² V^?1 s^?1, which is among the highest values for n‐type polymeric semiconductors in bottom‐gate top‐contact organic field‐effect transistors. Preliminary all‐polymer solar cell devices with P(TBAzDI‐TPD) as the electron acceptor and PTB7‐Th as the electron donor display a power conversion efficiency of 1.82 %.     

Protonation of Pyridyl‐Substituted TTF Derivatives: Substituent Effects in Solution and in the Proton–Electron Correlated Charge‐Transfer Complexes

Protonated pyridyl‐substituted tetrathiafulvalene electron‐donor molecules (PyH⁺‐TTF) showed significant changes in the electron‐donating ability and HOMO–LUMO energy gap compared to the neutral analogues and gave a unique N⁺?H???N hydrogen‐bonded (H‐bonded) dimer unit in the proton–electron correlated charge‐transfer (CT) complex crystals. We have evaluated these features from the viewpoint of the molecular structure of the PyH⁺‐TTF derivatives, that is, the substitution position of the Py group and/or the presence or absence of the ethylenedithio (EDT) group. Among 2‐PyH⁺‐TTF ( 1 o H⁺ ), 3‐PyH⁺‐TTF ( 1 m H⁺ ), 4‐PyH⁺‐TTF ( 1 p H⁺ ), and 4‐PyH⁺‐EDT‐TTF ( 2 p H⁺ ) systems, the para‐pyridyl‐substituted donors 1 p H⁺ and 2 p H⁺ exhibit more marked changes upon protonation in solution; a larger redshift in the intramolecular CT absorption band and a larger decrease in the electron‐donating ability. Furthermore, the EDT system 2 p H⁺ has the smallest intramolecular Coulombic repulsion energy. These differences are reasonably interpreted by considering the energy levels and distributions of the HOMO and LUMO obtained by quantum chemical calculations. Such substituent effects related to protonation were also examined by comparing the structure and properties of a new H‐bonded CT complex crystal based on 2 p H⁺ with those of its 1 p H⁺ analogue recently prepared by us: Both of them form a similar type of H‐bonded dimer unit, however, its charge distribution as well as the overall molecular arrangement, electronic structure, and conductivity were significantly modulated by the introduction of the EDT group. These results provide a new insight into the structural and electronic features of the PyH⁺‐TTF‐based proton–electron correlated molecular conductors.     

The Emergence of Organic Single‐Crystal Electronics

Organic semiconducting single crystals are perfect for both fundamental and application‐oriented research due to the advantages of free grain boundaries, few defects, and minimal traps and impurities, as well as their low‐temperature processability, high flexibility, and low cost. Carrier mobilities of greater than 10 cm² V^?1 s^?1 in some organic single crystals indicate a promising application in electronic devices. The progress made, including the molecular structures and fabrication technologies of organic single crystals, is introduced and organic single‐crystal electronic devices, including field‐effect transistors, phototransistors, p‐n heterojunctions, and circuits, are summarized. Organic two‐dimensional single crystals, cocrystals, and large single crystals, together with some potential applications, are introduced. A state‐of‐the‐art overview of organic single‐crystal electronics, with their challenges and prospects, is also provided.     

Extension of N‐Heteroacenes through a Four‐Membered Ring

The synthesis of novel π‐extended N‐heteroacenes, which have a large tetraazaacene subunit and a quinoxaline subunit connected through a four‐membered ring, is reported. They were studied with experimental and computational methods in comparison to the corresponding tetraazaacenes. As found from the DFT calculation, the four‐membered ring is a better linker than a five‐membered ring or a C?C single bond to extend N‐heteroacenes for a new design of n‐type semiconductors in terms of the spatial delocalization and energy level of LUMO as well as the reorganization energy. In solution‐processed thin film transistors, the π‐extended N‐heteroacenes are found to function as n‐type semiconductors with field effect mobility of up to 0.02 cm² V^?1 s^?1 under ambient conditions.     

From Linear to Angular Isomers: Achieving Tunable Charge Transport in Single‐Crystal Indolocarbazoles Through Delicate Synergetic CH/NH⋅⋅⋅π Interactions

Weak intermolecular interaction in organic semiconducting molecular crystals plays an important role in molecular packing and electronic properties. Here, four five‐ring‐fused isomers were rationally designed and synthesized to investigate the isomeric influence of linear and angular shapes in affecting their molecular packing and resultant electronic properties. Single‐crystal field‐effect transistors showed mobility order of 5,7‐ICZ (3.61 cm² V^?1 s^?1) >5,11‐ICZ (0.55 cm² V^?1 s^?1) >11,12‐ICZ (ca. 10^?5 cm² V^?1 s^?1) and 5,12‐ICZ (ca. 10^?6 cm² V^?1 s^?1). Theoretical calculations based on density functional theory (DFT) and polaron transport model revealed that 5,7‐ICZ can reach higher mobilities than the others thanks to relatively higher hole transfer integral that links to stronger intermolecular interaction due to the presence of multiple NH???π and CH???π(py) interactions with energy close to common NH???N hydrogen bonds, as well as overall lower hole‐vibrational coupling owing to the absence of coupling of holes to low frequency modes due to better π conjugation.     

Hot π‐Electron Tunneling of Metal–Insulator–COF Nanostructures for Efficient Hydrogen Production

A metal–insulator–semiconductor (MIS) photosystem based on covalent organic framework (COF) semiconductors was designed for robust and efficient hydrogen evolution under visible‐light irradiation. A maximal H₂ evolution rate of 8.42 mmol h^?1 g^?1 and a turnover frequency of 789.5 h^?1 were achieved by using a MIS photosystem prepared by electrostatic self‐assembly of polyvinylpyrrolidone (PVP) insulator‐capped Pt nanoparticles (NPs) with the hydrophilic imine‐linked TP‐COFs having =C=O?H?N= hydrogen‐bonding groups. The hot π‐electrons in the photoexcited n‐type TP‐COF semiconductors can be efficiently extracted and tunneled to Pt NPs across an ultrathin PVP insulating layer to reduce protons to H₂. Compared to the Schottky‐type counterparts, the COF‐based MIS photosystems give a 32‐fold‐enhanced carrier efficiency, attributed to the combined enhancement of photoexcitation rate, charge separation, and oxidation rate of holes accumulated in the valence band of the TP‐COF semiconductor.     

Metal‐Free Photocatalytic Hydrogenation Using Covalent Triazine Polymers

Photocatalytic hydrogenation of biomass‐derived organic molecules transforms solar energy into high‐energy‐density chemical bonds. Reported herein is the preparation of a thiophene‐containing covalent triazine polymer as a photocatalyst, with unique donor‐acceptor units, for the metal‐free photocatalytic hydrogenation of unsaturated organic molecules. Under visible‐light illumination, the polymeric photocatalyst enables the transformation of maleic acid into succinic acid with a production rate of about 2 mmol g^?1 h^?1, and furfural into furfuryl alcohol with a production rate of about 0.5 mmol g^?1 h^?1. Great catalyst stability and recyclability are also measured. Given the structural diversity of polymeric photocatalysts and their readily tunable optical and electronic properties, metal‐free photocatalytic hydrogenation represents a highly promising approach for solar energy conversion.     

Ion‐Pairing Assemblies Based on Pentacyano‐Substituted Cyclopentadienide as a π‐Electronic Anion

Pentacyanocyclopentadienide (PCCp^?), a stable π‐electronic anion, provided various ion‐pairing assemblies in combination with various cations. PCCp^?‐based assemblies exist as single crystals and mesophases owing to interionic interactions with π‐electronic and aliphatic cations with a variety of geometries, substituents, and electronic structures. Single‐crystal X‐ray analysis revealed that PCCp^? formed cation‐dependent arrangements with contributions from charge‐by‐charge and charge‐segregated assembly modes for ion pairs with π‐electronic and aliphatic cations, respectively. Furthermore, some aliphatic cations gave dimension‐controlled organized structures with PCCp^?, as observed in the mesophases, for which synchrotron XRD analysis suggested the formation of charge‐segregated modes. Noncontact evaluation of conductivity for (C₁₂H₂₅)₃MeN⁺ ? PCCp^? films revealed potential hole‐transporting properties, yielding a local‐scale hole mobility of 0.4 cm² V^?1 s^?1 at semiconductor–insulator interfaces.     

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 Nitrogen‐Rich 2D sp2‐Carbon‐Linked Conjugated Polymer Framework as a High‐Performance Cathode for Lithium‐Ion Batteries

A two‐dimensional (2D) sp²‐carbon‐linked conjugated polymer framework (2D CCP‐HATN) has a nitrogen‐doped skeleton, a periodical dual‐pore structure and high chemical stability. The polymer backbone consists of hexaazatrinaphthalene (HATN) and cyanovinylene units linked entirely by carbon–carbon double bonds. Profiting from the shape‐persistent framework of 2D CCP‐HATN integrated with the electrochemical redox‐active HATN and the robust sp² carbon‐carbon linkage, 2D CCP‐HATN hybridized with carbon nanotubes shows a high capacity of 116 mA h g^?1, with high utilization of its redox‐active sites and superb cycling stability (91 % after 1000 cycles) and rate capability (82 %, 1.0 A g^?1 vs. 0.1 A g^?1) as an organic cathode material for lithium‐ion batteries.