A [2]Rotaxane-Based Circularly Polarized Luminescence Switch

A rotaxane-based molecular shuttle
has been synthesized in which
the switching of the position of a fluorescent macrocycle on the thread
turns “on” or “off” the circularly polarized
luminescence (CPL) of the system while maintaining similar fluorescence
profiles and quantum yields in both states. The chiroptical activity
relies on the chiral information transfer from an ammonium salt incorporating d- or l-phenylalanine residues as chiral stereogenic
covalent units to an otherwise achiral crown ether macrocycle bearing
a luminescent 2,2′-bipyrene unit when they interact through
hydrogen bonding. Each enantiomeric thread induces CPL responses of
opposite signs on the macrocycle. Upon addition of base, the switching
of the position of the macrocycle to a triazolium group disables the
chiral information transfer to the macrocycle, switching “off”
the CPL response. The in situ switching upon several acid/base cycles
is also demonstrated.