No abstract

A simple Schiff base type fluorescent receptor was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an "off-on-type" mode with high selectivity in the presence of Zn(2+) ion. The addition of EDTA quenches the fluorescence of receptor 1-Zn(2+) complex, making receptor 1 a reversible chemosensor. The selectivity of 1 for Zn(2+) is the consequence of combined effects of CHEF, C=N isomerization and inhibition of ESIPT.

A simple 2-hydroxy-1-naphthaldehyde (receptor 1) serves as a selective chemosensor for Al(3+) based on chelation-enhanced fluorescence (CHEF). The receptor 1 exhibited a high association constant with micromolar detection for Al(3+) in EtOH-H(2)O solution.

A simple Schiff-base receptor 2 was prepared. It exhibits an “off-on-type” mode with high sensitivity in the presence of Al3+. The receptor 2 exhibited a high association constant with submicromolar detection for Al3+ in EtOH–H2O (95:5 v/v) solution. The addition of EDTA quenches the fluorescence of the receptor 2·Al3+ complex offering receptor 2 as a reversible chemosensor.

Sugar-aza-crown ether-based cavitand 1 can act as a selective turn-on fluorescence sensor for hydrogen sulfate ion in methanol among a series of tested anions. Spectroscopic studies, particularly NMR spectroscopy, revealed that the C-H hydrogen bonding between 1,2,3-triazole ring of cavitand 1 and hydrogen sulfate ion is crucial for the high selectivity of the receptor for hydrogen sulfate.