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HOMO-LUMO coupling: the fourth rule for highly effective molecular rectifiers

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Title: HOMO-LUMO coupling: the fourth rule for highly effective molecular rectifiers
Authors: Thong, AZ
Shaffer, MS
Horsfield, AP
Item Type: Journal Article
Abstract: Three rules for creating highly effective unimolecular rectifiers that utilize asymmetric anchoring groups have been proposed by Van Dyck and Ratner [Ratner et al., Nano Lett., 2015, 15, 1577–1584]. This study investigates their proposed rectification mechanism in a functionalised azafullerene system (4TPA–C60) and identifies a fourth rule. NEGF-DFT shows that 4TPA–C60 fulfills the three design rules and finds that a saturated bridge is not required to fulfil the third rule, contrary to previous belief. Instead a twisted-π bridge decouples the donor and acceptor states whilst still providing a high conductance pathway. The molecular junction has a calculated rectification ratio of 145 at a bias of ±1 V and the U-type rectification mechanism is driven by the pinning of the HOMO to the LUMO when the device is forward biased, but not when reverse biased. The switching behaviour is a result of a charge dipole forming at different interfaces for different bias directions. An additional design rule is thus proposed: charge transport should allow bias dependent coupling of filled to unfilled states. The findings in this work not only help in understanding charge transport in molecular rectifiers, but also have wider implications for the design of molecular resonant tunneling devices.
Issue Date: 26-May-2017
Date of Acceptance: 26-May-2017
URI: http://hdl.handle.net/10044/1/48761
DOI: https://dx.doi.org/10.1039/C7NR01680H
ISSN: 2040-3372
Publisher: Royal Society of Chemistry
Start Page: 8119
End Page: 8125
Journal / Book Title: Nanoscale
Volume: 9
Copyright Statement: © The Royal Society of Chemistry 2017
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
The Leverhulme Trust
Funder's Grant Number: EP/G007314/1
F/07 058/BK
Keywords: Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Physics, Applied
Chemistry
Science & Technology - Other Topics
Materials Science
Physics
SELF-ASSEMBLED MONOLAYERS
UNIMOLECULAR RECTIFIERS
GOLD ELECTRODES
RECTIFICATION
C-60
JUNCTIONS
DESIGN
DIODES
SPECTROSCOPY
SURFACES
10 Technology
02 Physical Sciences
03 Chemical Sciences
Publication Status: Published
Appears in Collections:Faculty of Engineering
Materials
Chemistry
Faculty of Natural Sciences



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