Twisted Intramolecular Charge Transfer‐Based Fluorometric Detection of D‐fructose by Boronic Acid‐Containing BF2‐β‐Diketonate Complexes

Fluorescent BF₂-β-diketonate complexes with boronic acid moieties were synthesized. Dimethylaminophenyl-group-containing complexes showed a twisted intramolecular charge transfer (TICT) property. Complexes displayed pH response with a large change in emission intensity. Emission intensity of the complexes increased with increasing amounts of D-fructose.

Abstract

Novel BF₂-β-diketonate complexes 1–4 bearing phenylboronic acid moieties and methoxyphenyl or dimethylaminophenyl groups were synthesized and their photophysical properties, pH response, and reactivity to D-fructose were evaluated. Complexes 1 and 2 bearing a methoxyphenyl group luminesced with high intensity in a range of non-polar to polar solvents, except in DMSO, whereas complexes 3 and 4 containing a dimethylaminophenyl group with twisted intramolecular charge transfer (TICT) properties showed a dramatic decrease in luminescence intensity with increasing solvent polarity. The luminescence intensity of complexes 1 and 2 decreased with increasing pH due to intermolecular vibration which associated with hydrogen bonding between the complexes and solvent water molecules, whereas it increased when they reacted with D-fructose due to the suppression of the intermolecular vibration. In contrast, the luminescence intensity of complexes 3 and 4 increased with increasing pH and upon reaction with D-fructose due to the loss of its TICT properties. The photophysical properties of complexes 1–4 and the TICT properties of complexes 3 and 4 were supported by density functional theory calculations.

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