Imperial College London

Prof Milo Shaffer

Faculty of Natural SciencesDepartment of Chemistry

Professor of Materials Chemistry



+44 (0)20 7594 5825m.shaffer Website




Mr John Murrell +44 (0)20 7594 2845




M221Royal College of ScienceSouth Kensington Campus






BibTex format

author = {Thong, AZ and Shaffer, MS and Horsfield, AP},
doi = {10.1039/C7NR01680H},
journal = {Nanoscale},
pages = {8119--8125},
title = {HOMO-LUMO coupling: the fourth rule for highly effective molecular rectifiers},
url = {},
volume = {9},
year = {2017}

RIS format (EndNote, RefMan)

AB - 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.
AU - Thong,AZ
AU - Shaffer,MS
AU - Horsfield,AP
DO - 10.1039/C7NR01680H
EP - 8125
PY - 2017///
SN - 2040-3372
SP - 8119
TI - HOMO-LUMO coupling: the fourth rule for highly effective molecular rectifiers
T2 - Nanoscale
UR -
UR -
VL - 9
ER -