Photoswitching
Azobenzene Derivatives in Single Molecule
Junctions: A Theoretical Insight into the <i>I</i>/<i>V</i> Characteristics
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Abstract
The <i>I</i>/<i>V</i> characteristics of several
photoswitching azobenzene derivatives connected to two gold electrodes
to form single-molecule junctions are investigated within the nonequilibrium
Green’s function formalism coupled to density functional theory.
We focus here on the changes in the <i>I</i>/<i>V</i> characteristics as a function of the length and degree of fluorination
of the conjugated backbones as well as different coupling strength
at the electrodes (chemisorption versus physisorption) upon <i>trans</i>/<i>cis</i> isomerization. The calculations
illustrate that the conductance is larger for the <i>trans</i> isomer when the molecule is chemisorbed at both electrodes. However,
a larger conduction for the <i>cis</i> isomer is found in
the presence of a physisorbed contact at one electrode for specific
geometries of the isomer in the junction, in full consistency with
the apparent discrepancies observed among experimental measurements.
The <i>I</i>/<i>V</i> curves are fully rationalized
by analyzing the evolution under bias of the shape of the transmitting
molecular orbitals