Catechol derivatives as fluorescent chemosensors for wide-range pH detection

The synthesis and characterization of a new family of catechol derivatives designed to behave as fluorescent chemosensors for wide-range pH detection has been described. These compounds were prepared by covalently coupling a catechol unit with other aromatic rings, thus obtaining π-delocalized systems with both pH-responsive groups and fluorescent behavior. In the case of a pyridine-catechol derivative, this leads to up to three different protonation states with distinct optical properties in organic media, as corroborated by density functional theory calculations. By applying dualwavelength detection techniques, this compound shows complementary "off-on-off" and "on-off-on" emission profiles upon pH variation, a behavior that can be exploited to perform acidity detection over a broad pH range. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.