A water-soluble bithiophene with increased photoluminescence efficiency and metal recognition ability

A new water-soluble tri- tert -butyl-bithiophenesulfonamide ( α2-tbS ) was synthesized and a comprehensive spectroscopic and photophysical study was undertaken in organic solvents and water at different pH values. In contrast to the behaviour found for the parent (and un-substituted) α,α′-bithiophene ( α2 ), in which radiationless decay processes are the main excited-state deactivation channels, the tert -butylsulfonamide derivative presents a significant fluorescence quantum yield ( F ) ( ca. one order of magnitude higher than that of α2 ). The high F allowed further exploring α2-tbS as a selective fluorimetric sensor for metal ions. A strong selectivity towards Cu( ii ) is observed at neutral pH values, whereas at pH = 9.5 a strong quenching upon the addition of Hg( ii ) is observed. An additional high sensitivity of 0.64 ± 0.02 ppm towards Cu( ii ) was observed, well below 1.25 ppm (∼20 μM), the maximum value allowed in drinking water by the EPA. A water soluble and highly fluorescent bithiophene was obtained. The excited state behavior is fully characterized and with tert -butylsulfonamide derivatization the recognition of Cu( ii ) and Hg( ii ) with high selectivity was observed.