Searching for new luminescent chemosensors for metal ions

Aiming to develop new fluorescent chemosensors for biological and environmental applications, we have designed and synthesized new chemical species able to reversibly bind alkali, earth-alkali, and transition metal ions. For signaling the binding of the target analyte, we have inserted in the structure of the chemosensors different luminophores, such as dioxyxanthone derivatives, dansyl derivatives, ruthenium complexes, and hydroxyquinoline derivatives. In solution, the binding is always signaled by pronounced changes in the photophysical properties of the inserted luminophore such as emission wavelength and intensity, and excited state lifetime. The mechanism for the signal transduction strongly depends on the chosen receptor and luminophore moieties, and has been investigated in detail by means of steady state and time resolved spectroscopy. In all cases, the synthesized chemosensors have proved to be chemically and photochemically stable. Good selectivity and affinity has been obtained with different sensors for K+, Mg2+, Ba2+, Zn2+, Ni2+ and Cu2+, even in physiological pH conditions. Moreover the use of an array of these sensors in optodes could lead to the construction of the so called electronic tongues. Ail these features make these sensors promising candidates for analytical applications.