New Luminescent Cyclometalated Iridium(III) Diimine Complexes as Biological Labeling Reagents

Abstract

We report the synthesis, characterization, and photophysical and electrochemical properties of thirty luminescent cyclometalated iridium(III) diimine complexes [Ir(N-C)(2)(N-N)](PF(6)) (HN-C = 2-phenylpyridine, Hppy; 2-(4-methylphenyl)pyridine, Hmppy; 3-methyl-1-phenylpyrazole, Hmppz; 7,8-benzoquinoline, Hbzq; 2-phenylquinoline, Hpq; N-N = 4-amino-2,2'-bipyridine, bpy-NH(2); 4-isothiocyanato-2,2'-bipyridine, bpy-ITC; 4-iodoacetamido-2,2'-bipyridine, bpy-IAA; 5-amino-1,10-phenanthroline, phen-NH(2); 5-isothiocyanato-1,10-phenanthroline, phen-ITC; 5-iodoacetamido-1,10-phenanthroline, phen-IAA). The X-ray crystal structure of [Ir(mppz)(2)(bpy-NH(2))](PF(6)) has also been investigated. Upon irradiation, all the complexes display intense and long-lived luminescence under ambient conditions and in 77-K glass. On the basis of the photophysical and electrochemical data, the emission of most of these complexes is assigned to an excited state of predominantly triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir) --> pi(N-N)) character. In some cases, triplet intraligand ((3)IL) (pi --> pi)(N-N or N-C(-)) excited states have also been identified. In view of the specific reactivity of the isothiocyanate and iodoacetamide moieties toward the primary amine and sulfhydryl groups, respectively, we have labeled various biological molecules with a selection of these luminescent iridium(III) complexes. The photophysical properties of the luminescent conjugates have been investigated. In addition, a heterogeneous assay for digoxin has also been designed on the basis of the recognition of biotinylated anti-digoxin by avidin labeled with one of the luminescent iridium(III) complexes.

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…Generally, the bound complexes exhibit luminescence properties that significantly differ from that of the free substrate, due to changes in rigidity and hydrophobicity of the surroundings. [267] Therefore, the facile monitoring of bioconjunction reactions or the investigation of binding affinities can be conducted utilizing such luminescent iridium(III) complexes. The progress in this emerging field of bioanalytical applications has been topic of a number of recent reviews by Lo and co-workers.…”

Synthetically Tailored Excited States: Phosphorescent, Cyclometalated Iridium(III) Complexes and Their Applications

“…[59] Thus, luminescent labels provide a facile method for monitoring bioconjugation reactions and quantifying the binding affinity between different substrates. [3,60] A comprehensive review of the role of iridiumA C H T U N G T R E N N U N G (III) and other transition-metal complexes in bioanalytical applications as well as methods for improving their luminescent properties was reported by Lo and co-workers in 2005. [3] Photocatalytic Water Splitting…”

Energy Transfer by a Hopping Mechanism in Dinuclear IrIII/RuII Complexes: A Molecular Wire?

“…[1,2] In particular, systems containing Ru II , [3][4][5][6] and Ir III , [7][8][9][10][11][12] components have been employed for the development of electroluminescent devices [4,[13][14][15][16] as well as for luminescent biological probes. [17][18][19][20][21][22] The attractive features: 1) luminescent excited-states, 2) high chemical and photochemical stability, and 3) tunability of the redox and excited-state energies, have in recent years generated an explosion of papers on iridium compounds, especially on neutral complexes containing cyclometallated ligands. [23][24][25][26][27] In particular, the possibility of tuning the emission color of the iridium iii complexes by choosing the appropriate substituents on the chelating ligands has been described.…”