Synthesis and development of dipicolylamine derivatives as new fluorescent chemosensors

Abstract

Di-2-picolylamine (DPA) is a powerful chelator for many transition metal ions. In this thesis, new DPA fluorescent chemosensors consisting of a fluorophore such as either naphthalimide or quinoline are developed. The first part deals with the synthesis of 1,8-naphthalimide derivatives linked 2-, 3-, 4-((bis(pyridin-2-ylmethyl)amino)methyl)aniline, and 4-amino-2-((bis(pyridin-2-ylmethyl)amino)methyl)phenol. The metal ion sensing experiments showed N3D was selective toward Ag+ with fluorescent enhancement in aqueous emitting green fluorescence under blacklight. The complexation of [N3D+Ag+] is a 1:1 stoichiometric binding with a limit of detection (LOD) 0.67 µM. Second part is the synthesis of oxazolidinonyl DPA derivatives by using self-developed halo-induced cyclization followed by substitution. 6QOD displayed a remarkable fluorescent enhancement in aqueous media with the presensce of Hg2+ and in CH3CN with the presensce of Fe3+ showing LOD 1.01 and 0.22 µM, respectively. The fluorescent color of both cases changed into green. The probe recognized Hg2+ or Fe3+ ions based on a 1:1 complexation. From the 1H NMR investigation, the probe binds with Hg2+ and Fe3+ as tetradentate and tridentate ligand, respectively. The sensing mechanism probably involves the inhibition of photoinduced electron transfer between DPA unit and quinoline. Furthermore, we also synthesized QAD derivatives that the linker of QOD derivatives was changed from oxazolidinone to acetamide in order to compare the sensing property in term of rigidity of the linker. 6QAD is selective toward both metal ions in the same manner as of 6QOD but with lower sensitivities.