Stereoselective Excited-State Isomerization and Decay Paths in cis-Cyclobiazobenzene

Herein, we have employed OM2/MRCI-based full-dimensional nonadiabatic dynamics simulations to explore the photoisomerization and subsequent excited-state decay of a macrocyclic cyclobiazobenzene molecule. Two S₁/S₀ conical intersection structures are found to be responsible for the excited-state decay. Related to these two conical intersections, we found two stereoselective photoisomerization and excited-state decay pathways, which correspond to the clockwise and counterclockwise rotation motions with respect to the N═N bond of the azo group. In both pathways, the excited-state isomerization is ultrafast and finishes within ca. 69 fs, but the clockwise isomerization channel is much more favorable than the counterclockwise one with a ratio of 74% versus 26%. Importantly, the present work demonstrates that stereoselective pathways exist not only in the photoisomerization of isolated azobenzene (AB)-like systems but also in macrocyclic systems with multiple ABs. This finding could provide useful insights for understanding and controlling the photodynamics of macrocyclic nanostructures with AB units as the main building units.