Tuning the Emission of Cationic Iridium (III) Complexes Towards the Red Through Methoxy Substitution of the Cyclometalating Ligand

Abstract

The synthesis, characterization and evaluation in solid-state devices of a series of 8 cationic iridium complexes bearing different numbers of methoxy groups on the cyclometallating ligands are reported. The optoelectronic characterization showed a dramatic red shift in the absorption and the emission and a reduction of the electrochemical gap of the complexes when a methoxy group was introduced para to the Ir-C bond. The addition of a second or third methoxy group did not lead to a significant further red shift in these spectra. Emission maxima over the series ranged from 595 to 730 nm. All complexes possessing a motif with a methoxy group at the 3-position of the cyclometalating ligands showed very short emission lifetimes and poor photoluminescence quantum yields whereas complexes having a methoxy group at the 4-position were slightly blue shifted compared to the unsubstituted parent complexes, resulting from the inductively electron withdrawing nature of this directing group on the Ir-C bond. Light-emitting electrochemical cells were fabricated and evaluated. These deep red emitters generally showed poor performance with electroluminescence mirroring photoluminescence. DFT calculations accurately modelled the observed photophysical and electrochemical behavior of the complexes and point to an emission from a mixed charge transfer state.

Iridium(III) 2‐Phenylbenzimidazole Complexes: Synthesis, Structure, Optical Properties, and Applications in Dye‐Sensitized Solar Cells

“…[11] The second and third methoxy groups in the phenyl unit of 3-methyl-2-phenylpyridine also gave rise to hypsochromic shifts of the absorption maxima of the corresponding Ir III complexes instead of the expected bathochromic shifts. [12] The addition of the second CF 3 group in the phenyl unit of 2-[2-(trifluoromethyl)phenyl]pyridine caused a small redshift of the absorption maxima, while increasing the HOMO-LUMO gap of the complex. [13] These examples clearly demonstrate that new experimental and theoretical data concerning the electronic structure of Ir III complexes are demanded.…”

Circularly Polarized Phosphorescent Electroluminescence from Chiral Cationic Iridium(III) Isocyanide Complexes

“…Both two complexes have irreversible oxidation and reduction waves as shown in Figure and the electrochemical data are summarized in Table . The first oxidation potential of complexes R1 and S1 occurs at about 1.10 V, which was attributed to the Ir‐centered oxidation . Additionally, in comparison with electrochemical data of R/S‐1,1′‐bi‐2‐naphthol and intermediate 4 or 6 as shown in Figures S35–S38 (Supporting Information), other oxidation potentials of complexes R1 and S1 can be assigned to the R/S‐1,1′‐bi‐2‐naphthol moiety.…”

A Novel Technique for Generating and Observing Chemiluminescence in a Biological Setting

“…Also, the encapsulation of the highly water-soluble [Ru(bpy) 3 ] 2+ in nanomaterials-both targeted and untargeted-may also allow for the visualization of lesions while they are being surgically removed 34,35,36 . Finally, modifying the coordination sphere of the metal complex reporter and/or changing the transition metal center itself represent attractive routes to modulate and fine-tune the emission wavelengths within the visible and NIR ranges 37,38 .…”