Figure 18.

Combining Zn²⁺ with either of the macrocycles 42 and 43 affords highly effective probes for pyrophosphate anion (PPi). A solution containing TPE/imidazolium macrocycle 42 and one equivalent of Zn(OAc)₂ reports PPi binding via an AIE mechanism, which gives rise to a significant fluorescence enhancement at 472 nm [118]. In a similar vein, the Zn²⁺ complex of methylquinoline-substituted azamacrocycle 43 has shown exceptional selectivity and sensitivity for PPi over other phosphorous-based anions, returning a 21-fold fluorescence increase in the presence of PPi (1 equivalent) via an ICT mechanism [119].