Possible performance improvement in [2]catenane molecular electronic switches

Abstract

Mechanically interlocked bistable supramolecular complexes are promising candidates of molecular electronics. Applying a multiscale computational approach, here we study the coherent charge transport properties of catenane monolayers sandwiched between Cu͑111͒ electrodes. We demonstrate the robust nature of electrical switching behavior with respect to the variations in the monolayer packing density and the type of electrodes, as well as the thermal fluctuations of the molecules. We propose that the asymmetry of molecule-electrode barriers can be utilized to improve the switching ratio. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2195087͔ Generation of supramolecules, large molecular aggregates composed of subunits held together by noncovalent interactions, through molecular recognition and selfassembly represents a promising route toward nanotechnology. 1 Prime examples are the ͓2͔catenane and ͓2͔rotaxane molecules 2 in which an electron-accepting tetracationic cyclobis͑paraquat-p-phenylene͒ ͑CBPQT 4+ ͒ cyclophane encloses either a ring-shaped or a linear backbone with two electron-donating stations, tetrathiafulvalene ͑TTF͒ and the 1,5-dioxynaphthalene ͑DNP͒ ͓Figs. 1͑a͒ and 1͑b͔͒. These molecules are designed to assume bistable conformations, CBPQT 4+ encircling the stronger donor TTF as the ground state co-conformation ͑GSCC͒ and CBPQT 4+ encircling the weaker donor DNP as the metastable state coconformation ͑MSCC͒ ͓Fig. 1͑c͔͒. Solid-state tunnel junctions based on catenane and rotaxane Langmuir-Blodgett monolayers were constructed, and the reversible electrical switching in ambient conditions was demonstrated. While the voltage-gated conformational change of the molecules between the off-state GSCC and the on-state MSCC was proposed as the switching mechanism, 3-6 the molecular origin of the switching was questioned 7 as seemingly contradictory experiments appeared. 8-10 Indeed, differentiating a molecularly inherent switching from a stochastic one is a difficult task, 11 because the charge transport in molecular scale junctions is strongly influenced by the moleculeelectrode contacts and conformational fluctuations of molecules. [12][13][14][15] In a recent work, 16 employing realistic catenane monolayer models sandwiched between Au͑111͒ electrodes , we explicitly showed that the electrical switching ͑between on and off͒ can originate from the energetic movement of frontier orbitals that accompanies the structural switching of the molecule ͑between GSCC and MSCC, respectively͒. However, there exist many potential noises in the device, so the molecularly inherent nature of the switching signal still needs to be demonstrated. In this letter, we assess the reliability of the identified electrical switching mechanism using a catenane device model that differs from the previous one in terms of the packing density and the type of electrodes as well as taking into account thermal fluctuations of the molecules. We, in particular, consider the role of moleculeelectrode barriers that should play an importan...

Efficiency of π−π Tunneling in [2]Rotaxane Molecular Electronic Switches

“…As described in section 3.2, however, we found that HOMO has the DNP (rather than TTF) origin within our calculations. This is the major difference between the present rotaxane device model and previous catenane device models. , We found a similar assignment in the five out of the total eight GSCC models that were used to obtain the average I − V curve shown in Figure . This is in contrast to our finding for the catenane device case, where all the models we considered had TTF-originated HOMO .…”

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Nanophase-Segregated Structures and Transport Properties in Sulfonated Poly(arylene ether sulfone) Multiblock Copolymer Membrane for Proton Exchange Membrane Fuel Cell

“…[88][89][90][91][92][93][94][95] The water is described using the F3C force field. 96 The force field parameters are reported in the original papers 75 96 97 and in our previous study 29 on hydrated Nafion.…”