A Bisphosphate Ligand for Zn²⁺ Ion Detection and Co-Crystallization with N-Rich Organic Molecules

Herein, a bisphosphate ligand with extended aromatic rings having methyl substitutes at ortho-position named as 3,3',5,5'-tetramethyl-[1,1'-biphenyl]-4,4'-diyl bis(dihydrogen phosphate) (tmbiphH₄) was utilized in zinc ion detection and the preparation of its cocrystals. The fluorescence sensing capability of tmbiphH₄ for Zn²⁺ ions confirms its high selectivity and sensitivity. Moreover, the density functional theory (DFT) calculations support the strong coordination between Zn²⁺ and the phosphate functionality of the ligand, consistent with the observed sensing behavior. As per the previous studies, this appears to be the first report of Zn²⁺ detection using a bisphosphate ligand, highlighting the potential of bisphosphate to address challenges associated with detecting spectroscopically silent metal ions. In parallel, the ligand ability to form supramolecule motifs in the form of cocrystals with N-rich organic molecules (imidazole, 4,4'-bipyridine, and 6-nitroquinoline) was explored. The single-crystal X-ray diffraction studies revealed distinct supramolecular architectures driven by hydrogen bonding and π-π stacking interactions, while thermogravimetric analysis confirmed their thermal stability. Thus, the ability of tmbiphH₄ of cocrystalizing with N-rich organic molecules confirmed its potential in supramolecular chemistry and functional material design. Collectively, the experimental and theoretical findings feature multi-functional nature of tmbiphH₄, showcasing its role as a fluorescent probe for biologically significant metal ions and as a versatile building block for supramolecular engineering.