Spectroscopic and photophysical characterization of fluorescent chemosensors for monosaccharides based on N-phenylboronic acid derivatives of 1,8-naphthalimide

Spectroscopic and photophysical properties of two fluorescent probes for monosaccharides are presented. Probes are based on the N-phenyl-1,8-naphthalimide structure having the boronic acid group [R-B(OH)(2)] in ortho in one case, and meta in the other case, positions of the N-phenyl group. Formation of the anionic form of the boronic acid group [R-B(OH)(3)(-)] induced a substantial decrease of the steady-state fluorescence of both compounds. Because no change in the fluorescence lifetime from the neutral to the anionic forms is observed, static quenching resulting from photoinduced electron transfer from the anionic form of the boronic acid is used to explain the decrease of the emission intensity. Both compounds show substantial decreases of their fluorescence intensity in the presence of sugars. In addition, this decrease of the fluorescence intensity is associated with an increase of the fluorescence lifetime for the ortho derivative while no effect on the lifetime is observed for the meta derivative. Both photoinduced electron transfer and steric hindrance are discussed to correlate the observed results.