Cyclometalated Ir(III) complexes based on 3,8-di(1H-pyrazol-4-yl)-1,10-phenanthroline: Acid/base-induced luminescence transformation and Cu2+-induced luminescence switching

The cyclometalated Ir(III) complex, Ir(ppy) 2 (phen-dipzH 2 ) ( Ir-1 ), was synthesized using the ligand 3,8-di(1H-pyrazol-4-yl)-1,10-phenanthroline (phen-dipzH 2 ) and the auxiliary ligand 2-phenylpyridine (ppy). Crystal structure analysis reveals that each {Ir(ppy) 2 } + unit is coordinated by a neutral phen-dipzH 2 ligand in Ir-1 . The packing arrangement of Ir-1 displays aromatic stacking interactions and [C–H…N] hydrogen bonding interactions between the [Ir(ppy) 2 (phen-dipzH 2 )] + cations. In solution, Ir-1 exhibits emission switching induced by acid/base changes, with the emission wavelength shifting from 562 nm (yellow color) in the neutral state to 618 nm (pink color) under acidic conditions and to 528 nm (gray color) under basic conditions. These shifts are attributed to the protonation and deprotonation of the pyrazole units, which is confirmed by 1 H NMR spectra. Additionally, Ir-1 demonstrates high selectivity and sensitivity toward Cu 2+ ions, with a detection limit as low as 9.47 μM compared to other metal ions. The acid/base-responsive phosphorescence of Ir-1 has also been successfully utilized in the development of paper strip-based devices for urea detection.