Exploring the Photophysical Properties of Iridium (III) Complexes Using TD-DFT: A Comprehensive Study

Organic light-emitting diodes (OLEDs) are prominent in various applications, including screen displays, medical devices, and chemical sensors, due to their low power consumption, fast response speed, and high-resolution capability. Phosphorescent emitters, especially cyclometalated Ir(III) complexes, are particularly significant in OLEDs because they enable internal quantum efficiencies of up to 100% through strong spin-orbit coupling (SOC). This study focuses on the accurate characterization of singlet and triplet metal-to-ligand charge transfer (MLCT) states in Ir(III) complexes, which is essential for optimizing their performance. Using a combination of quantum mechanical methods, particularly time-dependent density functional theory (TDDFT) with optimally tuned range-separated functionals and the full-electron scalar relativistic Douglas-Kroll-Hess (DKH2) Hamiltonian, we evaluate the electronic structures and MLCT states of eight Ir(III) complexes. Our results highlight the efficacy of the tuned ω *B97X functional in predicting MLCT energies and higher-energy absorption peaks, demonstrating its superiority over conventional functionals like PBE0 and B3LYP. The inclusion of relativistic effects and SOC in our models ensures alignment with experimental absorption spectra, providing reliable benchmarks for computational approaches. This comprehensive analysis not only advances the understanding of MLCT transitions in phosphorescent materials but also aids in the design of new Ir(III) complexes with enhanced photophysical properties.