Abstract
We have developed two novel chemosensors 6-morpholino-8-(thiophen-2-yl)-1,2,3,4-tetrahydroquinoline-5-carbonitrile (L1) and 6-(methylthio)-8-(thiophen-2-yl)-1,2,3,4-tetrahydroquinoline-5-carbonitrile (L2) for selective identification of highly toxic Pd(2+)ions. The selectivity ofL1andL2was examined with a series of metal ions, among which Pd(2+)ions were recognized selectively with fluorescence turn-off performances in methanol with very low limits of detection (nM). Another compoundL3was synthesized and studied to understand the role of the thienyl ring during complexL1+ Pd(2+)andL2+ Pd(2+)formation. The fluorescence changes after addition of Pd(2+)were also observed through the "naked-eye" (under a 365 nm UV lamp). Quantum chemical (DFT) calculations have been carried out to acquire information about the stability of the chemosensors and their complexes with Pd2+(L1+ Pd(2+)andL2+ Pd2+), which suggested that complexL2+ Pd(2+)is more stable thanL1,L2and complexL1:Pd2+. A number of studies comprising Job plots, Stern-Volmer plots and detection limits illustrate the notable sensing abilities of the chemosensors with Pd(2+)ions, in which probeL2was found to be more applicable thanL1.