Boosting the Photoresponse of Azobenzene Single-Molecule Junctions via Mechanical Interlock and Dynamic Anchor

As the most classic photoisomerization system, azobenzene
has been
widely utilized as a building unit in various photoswitching applications.
However, attempts to build azobenzene-based single-molecule photoswitches
have met with limited success, giving low on/off ratios. Herein, we
demonstrate two designs of azobenzene-based photoresponsive single-molecule
junctions, based on mechanically interlocked diazocine and azobenzene-based
dynamic anchors, respectively. Molecular conductance measurements
using the scanning tunneling microscope breaking junction (STMBJ)
technique revealed dramatic conductance changes upon photoillumination,
achieving a high on/off ratio of ∼3.7. Using density functional
theory (DFT), we revealed peculiar quantum interference (QI) effects
in the diazocine molecular switch, indicating that diazocine is an
excellent candidate for molecular photoswitches. The asymmetric azobenzene
devices with a dynamic anchor exhibit switching behavior between a
fully off state and a highly conductive state associated with the trans/cis conformation transition. The
findings of this work not only present the design and development
of functional molecular devices based on azobenzene units but also
provide insight into the fundamental properties of light-induced quantum
interference in azobenzene-based molecular devices.