Iridium complexes having phosphrous ligands of large steric hindrance: photophysical comparison between solution state, solid state and electrospun fibers

Abstract In this work, two luminescent iridium complexes were synthesized with 2-phenyl pyridine (ppy) and two phosphine-based ligands. There was large steric hindrance in these phosphine-based ligands, so that there would be enough time for the excited state based on highly luminescent 3MLLCT (metal-to-ligand-ligand-charge-transfer) electronic transformation It was found that there was limited aggregation-induced phosphorescence emission (AIPE) effect in these two iridium complexes since their ligands with large steric hindrance minimized the intermolecular (π-π) interactions between molecules. A distorted octahedral coordination field was found in the single crystals of these two iridium complexes. A systematical comparison on the photophysical parameters of these two iridium complexes in solution state, in solid state and in electrospun fiber was carried out, so that the limited aggregation-caused quenching (ACQ) could be confirmed. The potential surface crossing and energy transfer in the excited state of these two iridium complexes were analyzed by means of density functional theory calculation and temperature-dependent emission spectra. The limited ACQ effect in these two iridium complexes was finally confirmed due to the large ligand steric hindrance, which allowed phosphorescent decay of excited state. High emission quantum yield (0.27) and long emissive lifetime (0.43 μs) in solid state were observed.