Influence of Triazole Substituents of Bis-Heteroleptic Ru(II) Probes toward Selective Sensing of Dihydrogen Phosphate

A series of seven new bis-heteroleptic Ru(II) probes (1[PF6](2)-7[PF6](2)) along with two previously reported probes (8[PF6] 2 and 9[PF6]2) containing a similar anion binding triazole unit (hydrogen bond donor) functionalized with various substituents are employed in a detailed comparative investigation for the development of superior selective probes for H2PO4-. Various solution- and solid-state studies, such as H-1-DOSY NMR, dynamic light scattering (DLS), single-crystal X-ray crystallography, and transmission electron microscopy (TEM), have established that the selective sensing of H2PO4- by this series of probes is primarily due to supramolecular aggregation driven enhancement of (MLCT)-M-3 emission. Intestingly, 1[PF6](2) and 7[PF6](2), having an electron-deficient (pi-acidic) aromatic pentafluorophenyl substituent are found to be superior probes for H2PO4- in comparison to the other aryl- and polyaromatic-substituted analogues (2[PF6](2)-6[PF6](2), 8[PF6](2), and 9[PF6](2)), in terms of a higher enhancement of the (MLCT)-M-3 emission band, a greater binding constant, and a lower detection limit. The superiority of 1[PF6](2) and 7[PF6](2) could be due to better supramolecular aggregation properties in the cases of pentafluorophenyl analogues via both hydrogen bonding and anion-fluorine/anion-pi noncovalent interactions.

Automated summary

A series of new bis-heteroleptic Ru(II) probes were used in a comparative study for the selective detection of H2PO4-, with 1[PF6](2) and 7[PF6](2) found to be superior in terms of MLCT-M-3 emission enhancement, binding constant, and detection limit, possibly due to better supramolecular aggregation properties.