[Ir(N^N^N)(C^N)L]⁺: A New Family of Luminophores Combining Tunability and Enhanced Photostability

Abstract

The relatively unexplored luminophore architecture [Ir(N^N^N)(C^N)L](+) (N^N^N = tridentate polypyridyl ligand, C^N = 2-phenylpyridine derivative, and L = monodentate anionic ligand) offers the stability of tridentate polypyridyl coordination along with the tunability of three independently variable ligands. Here, a new family of these luminophores has been prepared based on the previously reported compound [Ir(tpy)(ppy)Cl](+) (tpy = 2,2':6',2″-terpyridine and ppy = 2-phenylpyridine). Complexes are obtained as single stereoisomers, and ligand geometry is unambiguously assigned via X-ray crystallography. Electrochemical analysis of the materials reveals facile HOMO modulation through ppy functionalization and alteration of the monodentate ligand's field strength. Emission reflects similar modulation shifting from orange to greenish-blue upon replacement of chloride with cyanide. Many of the new compounds exhibit impressive room temperature phosphorescence with lifetimes near 3 μs and quantum yields reaching 28.6%. Application of the new luminophores as photosensitizers for photocatalytic hydrogen generation reveals that their photostability in coordinating solvent is enhanced as compared to popular [Ir(ppy)2(bpy)](+) (bpy = 2,2'-bipyridine) photosensitizers. Yet, the binding of their monodentate ligand emerges as a source of instability during the redox processes of cyclic voltammetry and mass spectrometry. DFT modeling of electronic structure is provided for all compounds to elucidate experimental properties.

An Unprecedented Family of Luminescent Iridium(III) Complexes Bearing a Six-Membered Chelated Tridentate C^N^C Ligand

“…Both cyclometalating carbon atoms are trans to the pyridine rings of the d t Bubpy, and the pyridyl unit of the bnpy-type ligands is trans to the chloride. This contrasts with the configuration of the Ir–Cl bond in previously reported Ir(III) complexes, 29,31,32,36,37,40,41 where an Ir–C bond is trans to the chloride ligand. For 1 – 3 , the Ir–Cl bond [2.375(3) Å for 1 , 2.3612(8) Å for 2 , and 2.369(2) Å for 3 ] is in the same range as that found for [Ir(tpy)(dmbpy)Cl] 2+ (2.357 Å, where tpy = 2,2′:6′,2″-terpyridine and dmbpy = 4,4′-dimethyl-2,2′-bipyridine) 42 but is significantly shorter (by ca.…”

“…0.1 Å) than the Ir–Cl bond in other cyclometalated tridentate Ir(III) complexes. 29,31,32,36,37,40,41 Given the short Ir–C C^N^C bonds [2.048(13) and 2.064(6) Å for 1 , 2.028(4) and 2.031(3) Å for 2 , and 2.017(7) and 2.027 Å for 3 ], this leads also to a correspondingly shorter Ir–N C^N^C bond [2.055(11) Å for 1 , 2.044(3) for 2 , and 2.032(7) Å for 3 ] compared to the Ir–N d t Bubpy bonds [2.158(10) and 2.159(11) Å for 1 , 2.127(3) and 2.140(3) Å for 2 , and 2.122(6) and 2.133(5) Å for 3 ]. The bite angle of the N^N ligand is unremarkable at 75.60(4)° for 1 , 75.85(12)° for 2 , and 76.1(2)° for 3 and in line with cationic Ir(III) complexes of the form [Ir(C^N) 2 (N^N)] + .…”

Hydrogen Photoevolution from a Green‐Absorbing Iridium(III)–Cobalt­(III) Dyad

“…These transitions correspond to metal/ligand‐to‐ligand charge transfer (MLLCT) from the cyclometalated iridium fragment (Ir‐C N C) to the terpyridine ligand. The energies of the transitions in the visible region of this complex are redshifted relative to those of [Ir(ppy) 2 (bpy)] + and [Ir(phbpy) 2 ] + because the LUMO energy of the 4′‐Py‐tpy ligand is much lower than that of bpy and phbpy 11g. The lower energy absorption relative to that of [Ir‐Py] + is due to the electron‐withdrawing effect of the cobalt(III) moiety, which stabilizes the LUMO of the 4′‐Py‐tpy.…”

Rigidly linking cyclometallated Ir(iii) and Pt(ii) centres: an efficient approach to strongly absorbing and highly phosphorescent red emitters

“…Meanwhile, point (ii) is potentially important with regards to the use of iridium complexes for solar energy conversion and photocatalysis, for example, where more efficient absorption across the visible region of the spectrum is desirable for practicable application. 15 Finally, we note that the combination of efficient low-energy [red] absorption and low-energy [red/NIR] emission is a key desirable criterion for bioimaging applications, to exploit the ''window of transparency'' of biological tissue in this region of the spectrum.…”