Boosting the Photoresponse\nof Azobenzene Single-Molecule\nJunctions via Mechanical Interlock and Dynamic Anchor

As the most classic photoisomerization system, azobenzene\nhas been\nwidely utilized as a building unit in various photoswitching applications.\nHowever, attempts to build azobenzene-based single-molecule photoswitches\nhave met with limited success, giving low on/off ratios. Herein, we\ndemonstrate two designs of azobenzene-based photoresponsive single-molecule\njunctions, based on mechanically interlocked diazocine and azobenzene-based\ndynamic anchors, respectively. Molecular conductance measurements\nusing the scanning tunneling microscope breaking junction (STMBJ)\ntechnique revealed dramatic conductance changes upon photoillumination,\nachieving a high on/off ratio of ∼3.7. Using density functional\ntheory (DFT), we revealed peculiar quantum interference (QI) effects\nin the diazocine molecular switch, indicating that diazocine is an\nexcellent candidate for molecular photoswitches. The asymmetric azobenzene\ndevices with a dynamic anchor exhibit switching behavior between a\nfully off state and a highly conductive state associated with the <i>trans</i>/<i>cis</i> conformation transition. The\nfindings of this work not only present the design and development\nof functional molecular devices based on azobenzene units but also\nprovide insight into the fundamental properties of light-induced quantum\ninterference in azobenzene-based molecular devices.