# Single-Molecule and π–π-Stacked Dimer Electron Transport in Carbazole and Folded Bicarbazole Derivatives in Molecular Junctions

## TL;DR

This study explores how the shape of flexible molecules affects their electrical conductivity at the single-molecule level.

## Contribution

The novel contribution is identifying how conformational changes in bicarbazole derivatives alter conductance mechanisms in molecular junctions.

## Key findings

- Flexible bicarbazole molecular wires switch conductance mechanisms from covalent to noncovalent π–π interactions.
- Single-molecule conductance is influenced by intramolecular interactions in molecular junctions.
- XPS and DFT reveal changes in electron transport pathways between SAM and single-molecule junctions.

## Abstract

The present work
provides insight into how the conformations of
flexible molecules can impact their single-molecule conductance. Six
thiol-substituted carbazole-based molecules are synthesized and characterized.
In four, two carbazole groups are joined by a linking group (1,3-propane
or meta-xylene) while the remaining two are model
monocarbazoles. Using a combination of X-ray photoelectron spectroscopy
(XPS), single-molecule conductance measurements, and density functional
theory (DFT) calculations, we demonstrate that upon transitioning
from a self-assembled monolayer (SAM) to a single-molecule junction,
the intermolecular interactions give way to intramolecular interactions.
This resulted in the flexible bicarbazole molecular wire switching
conductance mechanisms, which occurred primarily via the covalent
conjugated aromatic part of the molecule in the SAM to one including
conductance via noncovalent π–π interactions in
the single-molecule junction.