Molecular Self-recovery Features of Naphthyl Derivatives of Pyrimidine Bis Hydrazones: AIE, Mechanochromism and Al3+/Pyrophosphate (PPi) sensing

In this study, we have formulated and synthesized two compounds, HPHNP and HPOMNP, by engaging in chemical reactions that involve pyrimidine bishydrazides with 2-hydroxy-1-naphthaldehyde and 2-methoxy-1-naphthaldehyde, respectively. The compound HPHNP displays partial excited-state intramolecular proton transfer (ESIPT) characteristics in non-polar aprotic solvents due to a phenolic group. Both HPHNP and HPOMNP exhibit aggregation-induced emission (AIE) behavior in DMF-water mixtures, with varying water fractions. We investigated how HPHNP and HPOMNP behave when exposed to mechanical pressure and found a remarkable effect called molecular motion or self-recovery. Solid-state emission experiments, PXRD measurements, and theoretical analyses support this observation. Moreover, HPHNP serves as an efficient fluorescent probe for detecting Al³⁺ and pyrophosphate (PPi) ions in a DMF-water mixture with an 80% water fraction. The potential for solid-state motion is expected to have a crucial role in advancing molecular machines, and we anticipate that our findings will inspire other researchers by highlighting the utilization of intermolecular forces to achieve solid-state motion.