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[PF 6 ] 2 –7­[PF 6 ] 2 ) along with two previously reported probes (8­[PF 6 ] 2 and 9­[PF 6 ] 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 1H-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 3MLCT emission. Intestingly, 1­[PF 6 ] 2 and 7­[PF 6 ] 2 , having an electron-deficient (π-acidic) aromatic pentafluorophenyl substituent are found to be superior probes for H2PO4 – in comparison to the other aryl- and polyaromatic-substituted analogues (2­[PF 6 ] 2 –6­[PF 6 ] 2 , 8­[PF 6 ] 2 , and 9­[PF 6 ] 2 ), in terms of a higher enhancement of the 3MLCT emission band, a greater binding constant, and a lower detection limit. The superiority of 1­[PF 6 ] 2 and 7­[PF 6 ] 2 could be due to better supramolecular aggregation properties in the cases of pentafluorophenyl analogues via both hydrogen bonding and anion–fluorine/anion−π noncovalent interactions.