ABSTRACT
While a multitude of studies have appeared touting the use of molecules as electronic components, the design of molecular switches is crucial for the next steps in molecular electronics. In this work, single-molecule devices incorporating spiropyrans, made using break junction techniques, are described. Linear spiropyrans with electrode-contacting groups linked by alkynyl spacers to both the indoline and chromenone moieties have previously provided very low conductance values, and removing the alkynyl spacer has resulted in a total loss of conductance. An orthogonal T-shaped approach to single-molecule junctions incorporating spiropyran moieties in which the conducting pathway lies orthogonal to the molecule backbone is described and characterized. This approach has provided singlemolecule conductance features with good correlation to molecular length. Additional higher conducting states are accessible using switching induced by UV light or protonation. Theoretical modeling demonstrates that upon (photo)chemical isomerization to the merocyanine, two cooperating phenomena increase conductance: release of steric hindrance allows the conductance pathway to become more planar (raising the mid-bandgap transmission) and a bound state introduces sharp interference near the Fermi level of the electrodes similarly responding to the change in state. This design step paves the way for future use of spiropyrans in single-molecule devices and electrosteric switches.
ABSTRACT
Conductive inks for the future printed electronics should have the following merits: high conductivity, flexibility, low cost, and compatibility with wide range of substrates. However, the state-of-the-art conductive inks based on metal nanoparticles are high in cost and poor in flexibility. Herein, we reported a highly conductive, low cost, and super flexible ink based on graphene nanoplatelets. The graphene ink has been screen-printed on plastic and paper substrates. Combined with postprinting treatments including thermal annealing and compression rolling, the printed graphene pattern shows a high conductivity of 8.81 × 104 S m-1 and good flexibility without significant conductivity loss after 1000 bending cycles. We further demonstrate that the printed highly conductive graphene patterns can act as current collectors for supercapacitors. The supercapacitor with the printed graphene pattern as the current collector and printed activated carbon as the active material shows a good rate capability of up to 200 mV s-1. This work potentially provides a promising route toward the large-scale fabrication of low cost yet flexible printed electronic devices.
ABSTRACT
In this paper, for the first time, a laser direct writing technique is reported to form S- and N-doped graphene patterns on thin (0.3 mm thickness) polyethylene terephthalate (PET) and glass substrates from a specially formulated organic polybenzimidazole (PBI) ink, without thermally affecting the substrates and without the need for a metallic precursor. Unlike standard graphene ink printing, postcuring at high temperatures is not needed here, thus avoiding potential substrate distortion and damages. A UV laser beam of 355 nm wavelength is used to generate photochemical reactions to break the CS bond (2.8 eV) from dimethyl sulfoxide (DMSO, a component of the PBI ink) and the CN bond (3.14 eV) of PBI and form N- and S-doped graphene on the substrates. The sheet resistance of the laser-induced graphene is as low as 12 Ω sq-1 on PET, matching that of indium-tin oxide (ITO). The laser-written doped graphene shows hydrophilic characteristics, unlike pristine graphene. The S- and N-doped graphene allows the tailoring of bandgaps and thus controlling electrical and chemical properties. The optical transparency of the written graphene is below 10% which could be improved in the future. Potential applications include printing of flexible circuits and sensors, and smart wearables.
