Double Schiff base from thiophene-2,5-dicarboxylic acid as an "off-on-off" fluorescence sensor for the sequential detection of In³⁺and PPi

A double Schiff baseTas acceptor for metal ions derived from thiophene-2,5-dicarboxylic acid was designed and synthesized, and showed a high selectivity for In(3+)in a DMF/H2O buffer solution.Texhibited a 300-fold fluorescence enhancement upon the addition of In3+, accompanying a visual color change from dark (phi= 0.009) to bright yellow (phi= 0.197). The complexT-In(3+)could serve as a secondary sensor for PPi, which displayed recyclability upon the sequential addition of In(3+)and PPi. The detection limits were calculated to be 4.48 x 10(-8)M for In(3+)and 4.4 x 10(-6)M for PPi, respectively. According to Job's plot,Tand In(3+)tended to form 1 : 2 complexes with the binding affinity of 2.3 x 10(9)M(2). The fluorescence behavior ofTtowards In(3+)was primarily explained by the photoinduced electron transfer (PET) process based on theoretical calculations using Gaussian 09. Moreover,Tcould be applicable for indium detection in tap water with satisfactory recovery and RSD.