We report the synthesis, transport measurements, and electronic structure of conjugation-broken oligophenyleneimine (CB-OPI 6) molecular wires with lengths of ∼4 nm. The wires were grown from Au surfaces using stepwise aryl imine condensation reactions between 1,4-diaminobenzene and terephthalaldehyde (1,4-benzenedicarbaldehyde). Saturated spacers (conjugation breakers) were introduced into the molecular backbone by replacing the aromatic diamine with trans-1,4-diaminocyclohexane at specific steps during the growth processes. FT-IR and ellipsometry were used to follow the imination reactions on Au surfaces. Surface coverages (∼4 molecules/nm(2)) and electronic structures of the wires were determined by cyclic voltammetry and UV-vis spectroscopy, respectively. The current-voltage (I-V) characteristics of the wires were acquired using conducting probe atomic force microscopy (CP-AFM) in which an Au-coated AFM probe was brought into contact with the wires to form metal-molecule-metal junctions with contact areas of ∼50 nm(2). The low bias resistance increased with the number of saturated spacers, but was not sensitive to the position of the spacer within the wire. Temperature dependent measurements of resistance were consistent with a localized charge (polaron) hopping mechanism in all of the wires. Activation energies were in the range of 0.18-0.26 eV (4.2-6.0 kcal/mol) with the highest belonging to the fully conjugated OPI 6 wire and the lowest to the CB3,5-OPI 6 wire (the wire with two saturated spacers). For the two other wires with a single conjugation breaker, CB3-OPI 6 and CB5-OPI 6, activation energies of 0.20 eV (4.6 kcal/mol) and 0.21 eV (4.8 kcal/mol) were found, respectively. Computational studies using density functional theory confirmed the polaronic nature of charge carriers but predicted that the semiclassical activation energy of hopping should be higher for CB-OPI molecular wires than for the OPI 6 wire. To reconcile the experimental and computational results, we propose that the transport mechanism is thermally assisted polaron tunneling in the case of CB-OPI wires, which is consistent with their increased resistance.

We report the synthesis and electrical characterization of photoswitchable π-conjugated molecular wires. The wires were designed based on the previously reported oligophenyl­eneimine (OPI) wires [ Frisbie Frisbie Science20083201482] with a slight modification to incorporate the dithienylethene linker (the “photoswitch”) into the wire backbone (e.g., PS3-OPI 5; PS stands for the photoswitch, and the number following “PS’’ indicates its position within the OPI chain). Stepwise arylimine condensation reaction between 1,4-diamino­benzene and terephthalaldehyde (1,4-benzene­dicarbaldehyde) was employed to grow these wires from Au surfaces. To insert the “photoswitch” into the wire, 1,4-diaminobenzene was replaced with perfluoro-1,2-bis­(2-(4-amino­phenyl)-5-methyl­thien-4-yl)­cyclo­pentene (PS) at specific steps during the wire growth. A variety of surface characterization techniques were employed to investigate the structure of the wires including FT-IR spectroscopy, ellipsometry, cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy. The current–voltage ( I−V ) characteristics and resistances of the wires were acquired using conducting probe atomic force microscopy (CP-AFM). It was observed that all of the wires switch between high and low conductance modes (“ON” and “OFF” states corresponding to “closed” and “open” forms of the dithienyl­ethene linker, respectively) when irradiated by UV and visible light, respectively. Measuring the temperature dependence of the resistance revealed that the charge transport mechanism in the PS3-OPI 3 wire is tunneling (temperature independent) whereas longer PS3-OPI 5 and PS5-OPI 5 showed Arrhenius temperature dependence which is characteristic of a hopping mechanism. These experiments demonstrate light-based control of transport in molecular wires in the hopping regime, which ultimately may be useful for switching applications in molecular electronics.

The development of efficient and cost-effective catalysts for the oxygen evolution reaction is highly desirable for applications that are based on sustainable and clean technologies. In this study, we report...

The oxygen evolution reaction (OER) with its sluggish kinetics has imposed a significant barrier to the sustainable and green generation of hydrogen fuel (via electrolysis of water) and the development of metal-air batteries. In this study, we report an efficient and novel OER electrocatalyst based on NiSe 2 nanoparticles (NPs) and the naturally abundant halloysite clay mineral. The NiSe 2 /halloysite nanocomposite (NiSe 2 /H) was prepared by a simple one-step hydrothermal route. The electrocatalytic performance of the as-synthesized nanocomposite and its components (pristine NiSe 2 and halloysite) toward OER in 1.0 KOH solution was examined. The NiSe 2 /H nanocomposite exhibited a significantly enhanced catalytic activity in OER, with a low overpotential of 235 mV (measured at the current density of 60 mA cm −2 ), a Tafel slope of 146 mV dec −1 , and an outstanding long-term electrochemical durability for 16 h. Moreover, this nanocomposite required only 340 mV of overpotential to deliver the high current density of 250 mA cm −2 . Further investigations revealed that the improved catalytic performance of NiSe 2 /H can be attributed to the increased number of active sites and the optimized adsorption energy of OH − . These results indicate that NiSe 2 /H is a promising non-precious metal-based catalyst for alkaline OER.

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