The
bridge is a crucial component of the donor-bridge-acceptor
(D-B-A) architecture when studying electron transport properties and
molecular electronics. In this work, we explore the influence of the
bridge on molecular rectification using the nonequilibrium Green’s
function coupled with density functional theory. The systems considered
here are phenylene-based structures with and without amino (−NH2) and nitro (−NO2) substituents at the D
and A subunits, respectively. We define six different bridge structures
with linearly conjugated, cross-conjugated, and saturated bonds. We
calculate electron transport properties to obtain the current-voltage I–V characteristics and rectification
ratios (R) at low bias voltages. Our results show
that the I–V characteristics
of the systems without substituents are symmetrical, suggesting a
wire-like behavior. As expected, rectification is only present in
the systems with substituents. The R is maximum in
the D-XC-A system, with a value of 2.32 at 0.15 V, where XC is a cross-conjugated
bridge. However, we conclude that the best rectification performance,
with a R of 1.62, is that of the D-double-A system
since the conductance is not compromised to promote rectification.