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Charge Transport and Conductance Switching of Redox-Active Azulene Derivatives


Schwarz, Florian; Koch, Michael; Kastlunger, Georg; Berke, Heinz; Stadler, Robert; Venkatesan, Koushik; Lörtscher, Emanuel (2016). Charge Transport and Conductance Switching of Redox-Active Azulene Derivatives. Angewandte Chemie Internationale Edition, 55(39):11781-11786.

Abstract

Azulene (Az) is a non-alternating, aromatic hydrocarbon composed of a five-membered, electron-rich and a seven-membered, electron-poor ring; an electron distribution that provides intrinsic redox activity. By varying the attachment points of the two electrode-bridging substituents to the Az center, the influence of the redox functionality on charge transport is evaluated. The conductance of the 1,3 Az derivative is at least one order of magnitude lower than those of the 2,6 Az and 4,7 Az derivatives, in agreement with density functional theory (DFT) calculations. In addition, only 1,3 Az exhibits pronounced nonlinear current–voltage characteristics with hysteresis, indicating a bias-dependent conductance switching. DFT identifies the LUMO to be nearest to the Fermi energy of the electrodes, but to be an active transport channel only in the case of the 2,6 and the 4,7 Az derivatives, whereas the 1,3 Az derivative uses the HOMO at low and the LUMO+1 at high bias. In return, the localized, weakly coupled LUMO of 1,3 Az creates a slow electron-hopping channel responsible for the voltage-induced switching due to the occupation of a single molecular orbital (MO).

Abstract

Azulene (Az) is a non-alternating, aromatic hydrocarbon composed of a five-membered, electron-rich and a seven-membered, electron-poor ring; an electron distribution that provides intrinsic redox activity. By varying the attachment points of the two electrode-bridging substituents to the Az center, the influence of the redox functionality on charge transport is evaluated. The conductance of the 1,3 Az derivative is at least one order of magnitude lower than those of the 2,6 Az and 4,7 Az derivatives, in agreement with density functional theory (DFT) calculations. In addition, only 1,3 Az exhibits pronounced nonlinear current–voltage characteristics with hysteresis, indicating a bias-dependent conductance switching. DFT identifies the LUMO to be nearest to the Fermi energy of the electrodes, but to be an active transport channel only in the case of the 2,6 and the 4,7 Az derivatives, whereas the 1,3 Az derivative uses the HOMO at low and the LUMO+1 at high bias. In return, the localized, weakly coupled LUMO of 1,3 Az creates a slow electron-hopping channel responsible for the voltage-induced switching due to the occupation of a single molecular orbital (MO).

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2016
Deposited On:09 Feb 2017 14:14
Last Modified:09 Feb 2017 14:15
Publisher:Wiley-VCH Verlag
ISSN:1433-7851
Publisher DOI:https://doi.org/10.1002/anie.201605559

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