Synthesis of Rhodamine based turn-on Fluorescent Sensors for the Detection of Chromium Ions

Selective and sensitiverhodamine-based fluorescent Cr3+sensor, A. ESI mass spectrometry, NMR,and elemental analysis were used to analyze Sensor A, which has beensynthesized in high yield. Changes in fluorescence and absorptionwere used to assess its binding with different metal ions (Ca2+, Na+,Mn2+, Mg2+,Fe2+, Al3+,Ni2+, Fe3+,Co2+, Cu2+,Pb2+, Cr3+,Cd2+, Zn2+,Sn2+, and Hg2+). Compared to other metal ions, A exhibits goodsensitivity and highselectivity for Cr3+. The selectivity regardingA is confirmed by its high binding constant value with Cr3+. According to 1H NMR peak broadening tests, Cr3+binds to the sensor's hydroxyl groups and the imine group's nitrogen. Cr3+binding to sensor A's carbonyl oxygen is confirmed by the brightpink color that appears following Cr3+addition. The fluorescence enhancement as dosed the new absorption beyond 400 nm is further confirmed by the quantum yield values for the Cr3+-bound form and the ring-opened form of sensor A. According to the findings, the formation regardingthe ring-opened form of sensor A upon Cr3+binding is the mechanism responsible for the fluorescence enhancementand new absorption. It was found that A's sensitivity limit to Cr3+was 568 nM. With excessEDTA, the pink colorgoes away and the binding of Cr3+is reversible. As a result, this sensor couldbe employed as a reversible fluorescent sensor for Cr3+that is visible to the human eye.