Terpyridyl-based triphenylamine derivatives with aggregation-induced emission characteristics for selective detection of Zn2+, Cd2+ and CN− ions and application in cell imaging

Two terpyridyl triphenylamine derivative luminogens (DTPy-TPA and TPy-TPA) with aggregation-induced emission (AIE) characteristics were designed and synthesized. The number of terpyridyl units of these two compounds has a remarkable effect on the responses towards metal ions. DTPy-TPA with two terpyridyl groups on both sides displayed multi-response to Zn2+ and Cd2+ in THF solution along with distinct absorption and emission spectral changes, and obvious naked-eye color changes. However, TPy-TPA with one terpyridyl phenyl group didn't work. This should be resulted from the formation of supramolecular polymers or oligomers for DTPy-TPA to restrict the intramolecular motions, but dimers for TPy-TPA. Moreover, both of these two compounds in H2O/THF (9:1, v:v) solution could selectively and sensitively detect CN− with distinct fluorescence quenching, which was attributed to the nucleophilic addition of CN− to the α-position of the dicyanovinyl group and thus the free rotation of phenyl groups on TPA. The sensing mechanism of DTPy-TPA or TPy-TPA with CN− was confirmed by 1H NMR titration and Job's plot. Finally, based on their excellent photophysical properties, these two probes were successfully employed to detect CN− in living HEK293 cells using fluorescence bioimaging.