posted on 2023-11-07, 06:29authored byParisa Yasini, Stuart Shepard, Manuel Smeu, Eric Borguet
The modulation of charge transport through single molecules
can
be established by using the intrinsic characteristics of molecules
and the physical properties of their environment. Therefore, the impact
of the solvent on the electronic properties of molecules in the junction
and their charge transport behavior are of great interest. Here, for
the first time, we focused on charge transport through dimethylaminobenzonitrile
(DMABN). This molecule shows unique behavior, specifically noticeable
electronic structure modulations in bulk solvents, e.g., dual fluorescence
in a polar environment. Using the scanning tunneling microscopy break
junction (STM-BJ) technique, we find an order of magnitude increase
in conductance along with a second conductance value in polar solvents
over nonpolar solvents. Inspired by the twisted intramolecular charge
transfer (TICT) explanation of the famous dual fluorescence of DMABN
in polar solvents, we hypothesize stabilization of twisted DMABN molecules
in the junction in more polar solvents. Ab initio molecular dynamics
(AIMD) simulations using density functional theory (DFT) show that
DMABN can twist in the junction and have a larger dipole moment compared
to planar DMABN junction geometries, supporting the hypothesis. The
nonequilibrium Green’s function with the DFT approach (NEGF-DFT)
is used to calculate the conductance throughout the AIMD trajectory,
finding a significant change in the frontier orbitals and transmission
function at large internal twisting angles, which can explain the
dual conductance in polar solvents in STM-BJ experiments.