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

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 (MLLCT)-M-3 (metal-to-ligand-ligand-charge-transfer) electronic transformation It was found that there was limited aggregation-induced phos-phorescence emission (AIPE) effect in these two iridium complexes since their ligands with large steric hindrance minimized the intermolecular (pi-pi) interactions between molecules. A distorted octahedral coordination field was found in the single crystals of these two iridium complexes. A systematical com-parison 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 mu s) in solid state were observed. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this work, two luminescent iridium complexes were synthesized with phosphine-based ligands that had large steric hindrance, leading to highly luminescent excited states. Limited aggregation-induced phosphorescence emission (AIPE) effect was observed due to minimized intermolecular interactions between molecules. The photophysical parameters of these complexes in different states were compared, and density functional theory calculations were conducted to analyze the excited state behavior. The limited aggregation-caused quenching (ACQ) effect was confirmed, and high emission quantum yield and long emissive lifetime were observed in the solid state.