3,6-Disubstituted carbazole-based bisboronic acids with unusual fluorescence transduction as enantioselective fluorescent chemosensors for tartaric acid.

Carbazole-based bisboronic acids were found to be enantioselective fluorescent sensors for tartaric acid. The fluorescence response toward the enantiomers of tartaric acid at neutral pH displayed enhancement/diminishment. The sensor displays an unusual fluorescence intensity-pH relationship with diminished emission at acidic pH but enhanced emission at basic pH. Photoinduced electron transfer (PET) from the fluorophore to the protonated amine/phenylboronic acid unit is proposed to be responsible for this effect, which is rationalized by density functional theory (DFT) calculations.