Macrocyclic Bisbinaphthyl Fluorophores and Their Acyclic Analogues: Signal Amplification and Chiral Recognition

A series of optically active macrocyclic and acyclic bisbinaphthyls have been synthesized and
characterized. The structure of one of the bisbinaphthyl macrocycles has been established by a
single-crystal X-ray analysis. The UV and fluorescence spectra of these chiral compounds in various
solvents and at different concentrations are studied. Formation of excimers is observed for the
macrocyclic bisbinaphthyl compounds. Introduction of conjugated substituents to the 6,6‘-positions
of the binaphthyl units in the macrocycles leads to greatly amplified fluorescence signals. Using
the 6,6‘-substituted bisbinaphthyl macrocycles in place of the unsubstituted macrocycles allows a
2 orders of magnitude reduction in the sensor concentration for the fluorescence measurements.
These macrocycles have exhibited highly enantioselective fluorescent enhancements in the presence
of chiral α-hydroxycarboxylic acids and N-protected α-amino acids. They are useful as fluorescent
sensors for chiral recognition. The macrocycles show much greater enantioselectivity in the substrate
recognition than their acyclic analogues.