Cyclometalated iridium(III) chelates—a new exceptional class of the electrochemiluminescent luminophores

Abstract

Recent development of the phosphorescent cyclometalated iridium(III) chelates has enabled, due to their advantageous electrochemical and photo-physical properties, important breakthroughs in many photonic applications. This particular class of 5d6 ion complexes has attracted increasing interest because of their potential application in electroluminescence devices with a nearly 100 % internal quantum efficiency for the conversion of electric energy to photons. Similar to electroluminescence, the cyclometalated iridium(III) chelates have been successfully applied in the electricity-to-light conversion by means of the electrochemiluminescence (ECL) processes. The already reported ECL systems utilizing the title compounds exhibit extremely large ECL efficiencies that allow one to envisage many potential application for them, especially in further development of ECL-based analytical techniques. This review, based on recently published papers, focuses on the ECL properties of this very exciting class of organometallic luminophores. The reported work, describing results from fundamental as well as application-oriented investigations, will be surveyed and briefly discussed.Graphical abstractDepending on the chemical nature of the cyclometalated irdium(III) chelate different colours of the emitted light can be produced during electrochemical excitation.

Pyrazolo[4,3‐h]quinoline Ligand‐Based Iridium(III) Complexes for Electrochemiluminescence

“…Here we report a series of novel Ir III complexes having as ancillary ligand the 1H‐pyrazolo[4,3‐h]quinoline (pyqui) (Scheme ). Neutral iridium(III) complexes with cyclometalated ligand such as 2‐phenylpyridine (ppy), 2‐(2,4‐Difluorophenyl)pyridine (dfppy), 1‐phenylisoquinoline (piq), 2‐phenylquinoline (pq) and monoanionic ancillary ligand (e.g., acetylacetonate, pyridine triazoles), have been largely investigated for ECL . However, for all these ligands there is a degree of freedom between the two coordinating rings which lead to possible vibrations and a slight distorsion from planarity.…”

Iridium(III)‐Doped Core‐Shell Silica Nanoparticles: Near‐IR Electrogenerated Chemiluminescence in Water

“…Very intense ECL signals (visible by naked eyes) were obtained in this case for both complexes, upon linearly scanning the electrode potential between 0 and À2.1 V (Figure 4). The well-established mechanism for BPO-based ECL generation is illustrated in Equations (1)-(3): [14] BPO þ e À ! …”

“…[11][12][13][14][15] In general, iridium complexes show typical reversible, monoelectronic, redox properties, high photoluminescence (PL) efficiencies with relatively short lifetimes (in microseconds regime) and photo-and chemical-stability. Most importantly, unlike ruthenium(II) complexes that typically show emission centered between 600 and 650 nm, iridium(III) complexes have the ability to span the emission range from the near-IR [16,17] to deep blue, [18] which is useful in the development of multichannel analytical techniques.…”

“…[23,24] ECL studies employing iridium (III) complexes are currently focusing on systems with ECL emission in the visible region. [12,14,[25][26][27][28] On the other hand, the ability of generating ECL in near-IR is especially important for bioimaging application as biological autofluorescence and tissue absorption are minimized in the wavelength range 650-900 nm. [29,30] Near-IR ECL emission is usually obtained with quantum dots (such as CdSeTe, InAs, PbSe, CdP and CuInS) [31,32] and with gold nanoclusters in the pioneering works from Ding and coworkers.…”

Electrochemical Generation of Excited Intramolecular Charge‐Transfer States

“…These include Ru(II), Os(II), and Ir(III) complexes. Recently the latter have attracted growing attentions due to their flexibility in the design of new extremely efficient ECL systems emitting over the entire visible range of the UV‐vis radiations . Among many different Ir(III) complexes the cyclometalated Ir(III) chelate with three 2‐phenylpyridine ligands attached to the central metal core – fac ‐Ir(ppy) 3 has been found as an extremely efficient ECL luminophore.…”