Regioisomeric mono-pyridine functionalized triarylethene: Small AIEgens with isomeric effect and efficient platform for selective and sensitive detection of Pd2+ and Fe3+
Pyridine functionalized tetraarylethenes were earlier established as potential AIEgen (aggregation-induced emission active fluorogen) for numerous applications, whereas monopyridyl-linked triarylethene was reported to be non-AIEgen. In this work, we focus on to afford AIE-active mono-pyridine functionalized unsymmetrically substituted triarylethene where naphthyl, biphenyl, and 4-phenylpyridine rotors are attached with an alkene stator. Two regioisomeric pyridyl compounds are synthesized to study the isomeric effect on AIE-features. Both the regioisomeric compounds are found to be AIE-active with little variation. The reason behind the AIE-properties is substantiated by scanning electron microscopic studies, lifetime measurement, and also by studying the molecular packings in the single-crystal. The relatively large number of non-covalent interactions for 4-pyridyl isomer was somewhat harmful to exhibit fluorescence in the aggregate state, whereas beneficial for the strong fluorescence in the solid-state. Both these compounds are utilized for the nacked eye detection and identification of Fe3+ and Pd2+ individually by the extent of fluorescence quenching in the solution state with ~10-9 M detection limit and the solid-state till 10-3 M for Pd2+ and 10-2 M for Fe3+. The quenching mechanism is found to be the static and dynamic complexation of pyridyl N-atom with the metal ion. The fact is further proved by 1H NMR titration.