Light‐Triggered Reversible Open‐Close Motion of a Chiral Molecular Plier to Modulate Guest Binding
Light triggered configuration change (azobenzene) of one end of a molecular plier induces an interlocking motion at the other end (porphyrin unit) of the plier accompanied by a pivotal motion around the BINOL axis. E to Z isomerization decreases the distance between two porphyrin units which could be used for selective binding of pyridine-appended guests. Guest complexation with the plier increases the isomerization efficiency of azobenzene and decreases the thermal back isomerization rate.
A chiral molecular plier's design, synthesis, characterisation and operations are presented. The molecular plier encompasses three units: a BINOL unit which acts as a pivot as well as a chiral inducer, an azobenzene unit, which acts as a photo-switchable component and two zinc porphyrin, acting as a reporter. E to Z isomerisation persuaded by irradiating with 370 nm light alters the dihedral angle of the pivot BINOL unit, which adjusts the distance between two porphyrin units. The plier can be switched to its initial state by exposure to 456 nm light or heating at 50 °C. NMR, CD and molecular modelling supported the reversible switching and change in dihedral angle and distance between reporter moiety, which was further exploited for binding with several ditopic guests. The longest guest was found to form the strongest complex, R,R-isomer formed a stronger complex than S,S-isomer, Z-isomer of the plier formed stronger complex than the E-isomer with the guest. Moreover, complexation also increased the E-to-Z switching efficiency and decreased the thermal back isomerisation of the azobenzene unit.Zum Volltext
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