Photoswitchable Hopping Transport in Molecular Wires 4 nm in Length

Abstract

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.

A Chemically Soldered Polyoxometalate Single‐Molecule Transistor

“…[1] Ak ey aspect of molecular electronics from the perspective of chemists is,however, the possibility of exploring alarge chemical space to i) tune the device response to the desired range and magnitude,o btaining, in turn, important insights on structure-property relationships,a nd ii)study phenomena unique to the molecular and quantum world. Since the first pioneering studies in the late 1990s, [2] singlemolecule devices with behaviour like semiconductor-based diodes, [3,4] resistors, [5] switches, [6][7][8][9] and transistors [10][11][12][13] have been demonstrated, and the chemical complexity of the molecules used to fabricate junctions has rapidly increased. Stemming from the original studies employing simple aliphatic and conjugated rod-like oligoaryl moieties, [14] it is now common to read reports on molecular wires incorporating fused polyaromatic/heterocyclic systems, [15,16] supramolecular complexes, [17,18] organometallic centres, [19,20] and, more recently,p olynuclear clusters.…”

Tailoring the Schiff base photoswitching – a non-adiabatic molecular dynamics study of substituent effect on excited state proton transfer

“…Molecular switches, among other single molecule electronic units, are characterized as bi-stable systems in which reversible switching of various physical and chemical properties is achieved through exposure to external stimulus. The two forms of the switching molecule may differ by numerous attributes such as cis-trans isomerism [21][22][23][24] , chirality 25 , open-closed ring structure, [26][27][28] or tautomeric structure [29][30][31][32][33] . Up to date, the palette of experimentally studied factors allowing for the switching control includes an external electromagnetic irradiation 21,26,34 , electric current transmission 29,35 , static electric 22 and magnetic 26 fields, short-range forces 36 , temperature 26,37 , chemical reactions, 38,39 and mechanical stretching 40 .…”

Deliberate Switching of Single Photochromic Triads

“…The DCP unit undergoes a photocyclization reaction from the open to the closed form upon irradiation with light in the UV spectral range (280 nm–350 nm) and a photocycloreversion reaction upon irradiation with light in the visible spectral range (450 nm–650 nm). In recent work, it has been demonstrated that it is possible to modulate the electrical and/or optical properties of molecular dyads, organic transistors, molecular wires, or nanoparticle networks as a function of the light-induced alteration of the state of the DCP 20 21 22 23 24 25 .…”