Abstracts

The Ir^III ion readily forms coordination compounds with various classes of cyclometalating ligands, exhibiting attractive luminescent characteristics such as high quantum yields (Φ), modulation of both absorption and emission, as well as modulation of excited state lifetime. These complexes have promising applications in optoelectronics such as OLEDs, DSCs, LEECs, and several other optoelectronic devices. Additionally, they find application in the biological field, including oxygen sensing, bioimaging and agents in photodynamic therapy. Thus, this work describes the synthesis and spectroscopic characterization of two novel Ir^III complexes with N-oxide bridging ligand (N^O). The syntheses consisted on the preparation of the cyclometalated Ir^III dimer [Ir(Fppy)₂(μ-Cl)₂Ir(Fppy)₂], followed by the preparation of heteroleptic mononuclear [Ir(Fppy)₂pzdc] and dinuclear [Ir(Fppy)₂(µ-pzdc)Ir(Fppy)₂]: Fppy = 2-(2,4-difluorophenyl) and pzdc = 2,3-pyrazinedicarboxylic acid. Both complexes were structurally characterized by ¹H-NMR, elemental analysis, and FTIR-ATR. FTIR-ATR (ʋ_max/cm⁻¹): 1632 (ʋC=O)_pzdc, 1600, 1570, 1557 (ʋC=N, C=C)_fppy, 1333 (ʋCOO)_s, 1108 (ʋC=N, C=C)_pzdc. Coordination through the N^O site of the pyrazine is indicated by infrared spectra, wherein the pyrazine stretching bands disappear in the complex. Calculated CHN (found) for the structure IrC₂₈H₂₃N₄O₈F₄: C, 41.43% (41.50%); H, 2.86% (3.02%); N, 6.90%. Absorption and photoluminescence spectra were obtained in several solvents: DMSO, DCM, ACN, and MeOH. The complexes exhibited high molar absorptivity, attributed to singlet and triplet metal-to-ligand charge transfer (MLCT) and ligand-centered (LC) transitions, which were observed in the UV-Vis spectra. Excitation spectra showed a broad band with a similar profile for all tested solvents, for both complexes. In the emission spectra for each solvent tested, broad emissions ranging from yellow-orange to red were observed. Notably, the mononuclear complex exhibited emission maxima at approximately 510 and 617 nm in DMSO, 612 nm in DCM, 622 nm in ACN, and 630 nm in MeOH. Conversely, the dinuclear complex showed emission maxima at approximately 616.5 nm in DMSO, 624.5 nm in DCM, 617.5 nm in ACN, and 673.0 nm in MeOH. This difference in emission maxima is attributed to the solvatocromic effect that leads to structural differences, which influence the energy levels of the excited states. Additionally, the presence of two iridium centers in the dinuclear complex may lead to interactions between the metal centers, altering the electronic properties and resulting in a red-shifted emission compared to the mononuclear complex. The Φ for the mononuclear complex was determined: DMSO (7.7%), DCM (9.2%), ACN (6.9%), and MeOH (1.2%). Their photophysical properties indicate potential for applications in photonics, particularly notable for their high molar absorptivity and tunable emission in different solvents.