The mechanism of the change in fluorescence quenching by the amine in boronic acid-based carbohydratesensor molecules has been explored using density functional theory (DFT). The geometric constraints of thesystem have been studied in both intra- and intermolecular model systems of the boron−nitrogen (B−N)bonding interaction. The effect of the B−N bonding on the rate of electron-transfer (ET) quenching of theanthracene acceptor by an amine donor is considered using a theoretical model. The results suggest a newmechanism other than B−N bond strength change for fluorescent switching in biosensors that involve interactionof boron and nitrogen affected by boronate ester formation.