Rapid Synthetic Routes to Bipyridine-Based Metal–Organic Frameworks for Highly Selective Solvent Sensing

A series of known Pb(II) metal–organic frameworks (MOFs) have been synthesized from the reaction of PbX₂ (X = Cl, NO₃ and OAc) with bpy (where bpy = 4,4-bipyridine) using three synthetic methods, namely solvothermal, mechanochemical and liquid-assisted grinding (LAG). The synthesized compounds were characterized with powder X-ray diffraction (PXRD) patterns and matched with calculated X-ray diffraction patterns of reported crystal structures of Pb(II)-based MOFs. Interestingly, most of the compounds can be easily prepared by solvent-free methods either mechanochemically or by LAG methods. Finally, the successfully synthesized MOFs were subjected to photoluminescence study. Solid-state photoluminescence of the selected MOFs has been studied by suspending the MOFs particles in various solvents. Although they are not soluble in the solvents used, the MOFs show a fair amount of solvent-dependent emission quenching that roughly correlate with solvent polarity. With further exploration and investigations, the observed solvatochromic emission behavior of these compounds may find importance in solvent sensing applications.