Four phosphorescent iridium(III) complexes containing brominated 2,2′- bipyridine ligands as efficient chemosensors for OH− ions

Four cationic Ir(III) complexes Ir1–Ir4, [(4-fpiq)2Ir(L1)]PF6 (Ir1, 4-fpiq = 1-(4-fluorophenyl)isoquinoline, L1 = 4,4′-dibromo-2,2′-bipyridine), [(4-fpiq)2Ir(L2)]PF6 (Ir2, L2 = 5,5′-dibromo-2,2′-bipyridine), [(4-chopiq)2Ir(L1)]PF6 (Ir3, 4-chopiq = 1-(4-formylphenyl)isoquinoline), [(4-chopiq)2Ir(L2)]PF6 (Ir4) were synthesized using 2,2′-bipyridine derivatives as neutral ligands. These complexes show decent orange and red phosphorescence (λem = 576–618 nm) with quantum efficiencies of 0.13–0.37. The influence of substituents in the ligands on the photophysical and electrochemical properties of the Ir(III) complexes was investigated by UV–vis absorption and emission spectra and cyclic voltammograms and simulated by density functional theory (DFT) calculations. Upon addition of OH− ions to the solutions of Ir1–Ir4, all the complexes exhibited a turn-on response to OH− with a low detection limit on the order of 10−6 M, and high selectivity to OH− was demonstrated.