Halogen bonds in 2D supramolecular self-assembly of organic semiconductors

Weak interactions between bromine, sulphur, and hydrogen are shown to stabilize 2D supramolecular monolayers at the liquid–solid interface. Three different thiophene-based semiconducting organic molecules assemble into close-packed ultrathin ordered layers. A combination of scanning tunneling microscopy (STM) and density functional theory (DFT) elucidates the interactions within the monolayer. Electrostatic interactions are identified as the driving force for intermolecular Br⋯Br and Br⋯H bonding. We find that the S⋯S interactions of the 2D supramolecular layers correlate with the hole mobilities of thin film transistors of the same materials

Inkjet printed thin and uniform dielectrics for capacitors and organic thin film transistors enabled by the coffee ring effect

The deposition of a thin and uniform dielectric layer is required for high performance printed capacitors and thin film transistors (TFTs), however this is difficult to achieve with printing methods. We have demonstrated inkjet-printed dielectrics with a uniform thickness from 70 nm to 200 nm by taking advantage of the coffee ring effect. A high capacitance per unit area of 230 pF/mm2 is achieved from capacitors with linear morphologies fully printed onto flexible substrates. We also demonstrate organic TFTs with an average mobility of 0.86 cm2/Vs and a source drain current of 57 \u3bcA obtained with a supply voltage of 15 V. This performance was shown to be consistent, with a standard deviation of 15% obtained from hundreds of printed organic TFTs on PET substrates. This consistency was further validated by the production of functional NAND, NOR, AND and OR logic gates. Our results demonstrate that the coffee ring effect, which is usually viewed as undesirable, can enable higher performance in printed electronic devices.Peer reviewed: YesNRC publication: Ye

Tuning the Electronic Properties of Poly(thienothiophene vinylene)s via Alkylsulfanyl and Alkylsulfonyl Substituents

The use of alkylsulfanyl and alkylsulfonyl side chains are demonstrated to be a useful synthetic strategy for tuning the electronic properties of organic semiconductors, as shown in thienothiophene vinylene polymers. By changing the oxidation state of sulfanyl to sulfonyl, we lower the HOMO and LUMO energy levels of our substituted polymers, as well as enhance their fluorescence. Fine-tuning of the energy levels was achieved by combining sulfanyl and sulfonyl substituted thienothiophene monomers through random polymerization, yielding polymers with low-band gaps (1.5 eV) yet benefiting from a structurally uniform conjugated backbone. The effects of these functional side chains are presented through DFT calculations, UV–vis, fluorescence, and electrochemical measurements, as well as crystallographic analysis of a sulfanyl-substituted oligomer. The semiconducting properties of the new polymers are studied in OFET and OPV devices

Tuning the Electronic Properties of Poly(thienothiophene vinylene)s via Alkylsulfanyl and Alkylsulfonyl Substituents

The use of alkylsulfanyl and alkylsulfonyl side chains are demonstrated to be a useful synthetic strategy for tuning the electronic properties of organic semiconductors, as shown in thienothiophene vinylene polymers. By changing the oxidation state of sulfanyl to sulfonyl, we lower the HOMO and LUMO energy levels of our substituted polymers, as well as enhance their fluorescence. Fine-tuning of the energy levels was achieved by combining sulfanyl and sulfonyl substituted thienothiophene monomers through random polymerization, yielding polymers with low-band gaps (1.5 eV) yet benefiting from a structurally uniform conjugated backbone. The effects of these functional side chains are presented through DFT calculations, UV–vis, fluorescence, and electrochemical measurements, as well as crystallographic analysis of a sulfanyl-substituted oligomer. The semiconducting properties of the new polymers are studied in OFET and OPV devices

Pentacenobis(thiadiazole)dione, an n‑Type Semiconductor for Field-Effect Transistors

A new heteroacenequinone, pentaceno­[2,3-<i>c</i>:9,10-<i>c</i>′]­bis­([1,2,5]­thiadiazole)-6,13-dione (PBTDQ), with two peripheral thiadiazole rings was synthesized, and its solid-state properties were characterized. The fused planar structure with a low-lying LUMO and low reorganization energy facilitates electron transport, affording μ_e values of up to 0.11 cm² V^–1 s^–1 in field-effect transistor devices

Transformation Between 2D and 3D Covalent Organic Frameworks via Reversible [2+2] Cycloaddition

We report the first transformation between crystalline vinylene-linked two-dimensional (2D) polymers and crystalline cyclobutane-linked three-dimensional (3D) polymers. Specifically, absorption-edge irradiation of the 2D poly(arylenevinylene) covalent organic frameworks (COFs) results in topological [2+2] cycloaddition cross-linking the π-stacked layers in 3D COFs. The reaction is reversible and heating to 200°C leads to a cycloreversion while retaining the COF crystallinity. The resulting difference in connectivity is manifested in the change of mechanical and electronic properties, including exfoliation, blue-shifted UV-Vis absorption, altered luminescence, modified band structure and different acid-doping behavior. The Li-impregnated 2D and 3D COFs show a significant ion conductivity of 1.8×10−4 S/cm and 3.5×10−5 S/cm, respectively. Even higher room temperature proton conductivity of 1.7×10-2 S/cm and 2.2×10-3 S/cm was found for H2SO4-treated 2D and 3D COFs, respectively