We report a novel sensitive, selective, and reversible turn-on fluorescent Cr3+ sensor, A, based on rhodamine and 3,4-dihydroxy benzaldehyde units. Turn-on fluorescent sensing of Cr3+ is very important as Cr3+ normally quenches the fluorescence through intersystem crossing. Sensor A was synthesized in high yield and its binding with various metal ions (Na+, Ca2+, Mg2+, Mn2+, Al3+, Fe2+, Fe3+, Ni2+, Cu2+, Co2+, Cr3+, Pb2+, Zn2+, Cd2+, Hg2+, Sn2+) was examined through changes in absorption and fluorescence. A shows high selectivity and good sensitivity toward Cr3+ over other metal ions. The high binding constant value of A with Cr3+ confirms its selectivity. 1H NMR measurements indicates that Cr3+ binds with the nitrogen of the imine group and the hydroxyl groups of the sensor. The bright pink color upon Cr3+ addition confirms the binding to the carbonyl oxygen of sensor A. The quantum yield values for the ring-opened form of sensor A and the Cr3+-bound form also confirm the fluorescence enhancement. From the results, the mechanism behind the fluorescence enhancement and new absorption upon Cr3+ binding is attributed to the formation of the ring-opened form of sensor A upon Cr3+ binding.

Rhodamine based turn-on fluorescent sensor for the detection of chromium ions

251st National Meeting (2016)

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