Donor–acceptor biaryl lactones: pH induced molecular switches with intramolecular charge transfer modulation

The physical properties of biaryl-containing compounds are known to be highly dependent on molecular geometry. We report the syntheses and fundamental spectroscopic study of two donor–acceptor biaryl lactone (6H-benzo[c]chromen-6-one) pH-driven switches. These compounds have been determined to rapidly and efficiently switch between two geometric states upon cycling of acidic or basic stimuli. The planar lactone state exhibits enhanced intramolecular charge transfer (ICT) between the donor and acceptor units which is instantly attenuated upon addition of basic stimuli. The resulting lactone cleavage enables aryl–aryl bond rotation thus decreasing the extent of conjugation between the rings. Each state is readily identifiable by the significant changes that occur in their respective UV–vis spectra and luminescent character, indicative of the facile modulation of extended conjugation by pH.