Controllable chirality in mechanically locked or coordinated molecules is essential for the development of functional molecular machines. Here, we systematically investigate how geometric tuning of azobenzene-based pliers governs chiral induction and dynamic helicity in coordinated molecular rotors. Four plier derivatives were synthesized by varying the separation and relative orientation of the pyridyl nitrogen atoms to establish clear structure-property relationships. These geometric modifications significantly influence photoswitching efficiency, thermal stability, and induced chiroptical responses. Compared with meta-pyridyl pliers, para-pyridyl analogues exhibit reduced photoisomerization efficiency and shorter thermal half-lives, trends that persist in their corresponding host-guest complexes. Axial coordination of achiral rotor guests restricts conformational freedom, enabling efficient chirality transfer and distinct circular dichroism responses. For shorter pliers, changing the rotor substituent from a meta-to an ortho-position switches the preferred helicity from M to P, while altering the ligand geometry from meta-to para-pyridyl with a constant rotor induces the opposite inversion. In contrast, longer pliers display diminished chiral discrimination due to increased separation from the chiral axis. Notably, light-induced azobenzene isomerization enables reversible helicity inversion in a selected host-guest pair, underscoring the importance of precise structural design for dynamic control of molecular helicity.
Sahoo et al. (Tue,) studied this question.