Investigation Of Iridium Complexes With Solid-state Enhanced Phosphorescent Emission (EPESS) Properties

Cyclometalated iridium(?) complexes have attracted much attention due to their applications in organic light-emitting diodes, light-emitting electrochemical cells, chemosensors, biolabeling and so on. However, iridium(?) complexes with high concentration show severe T-T annihilation, leading to quenching of the phosphorescence emission. Recently, some iridium(?) complexes exhibited enhanced phosphorescence emission in the solid state (EPESS), however the mechanism is still ambiguous. In this dissertation, eleven iridium(?) complexes with EPESS properties were synthesized by changing the structures of O^O ancillary ligands, and the effect of?-?stacking on EPESS were discussed. The work contains three parts as follows:1. The conjugation effects of?-diketonate ligands on EPESS properties of cyclometalated iridium(?) complexesTwo cyclometalated heteroleptic Ir(?) complexes (Ir(ppy)2(PMBP) and Ir(ppy)2(PMPAP)), containing one monoanionic?-diketonate ligand, have been synthesized and characterized by 1H NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Ir(ppy)2(PMBP), containing a low triplet energy level of the ancillary ligand PMBP, is EPESS-active. The?-?stacking of the ppy ligands between Ir(ppy)2(PMBP) molecules causes the formation of metal-to-ligand-ligand charge-transfer transition with a low energy level, resulting in EPESS, which was confirmed by crystal packing analysis and DFT calculations. Moreover, the application of EPESS-active Ir(ppy)2(PMBP) in cell imaging has been explored through embedding it into polymer nanoparticles (Ir(ppy)2(PMBP)-PNPs).2. EPESS properties of iridium(?) complexes and discussion of?-?stacking modelFour new iridium(?) complexes with EPESS properties were designed and synthesized. In the solid state, obvious?-?stacking (even extended?-?stacking) was observed in these crystals, which was confirmed by theoretical calculations. A model containing perpendicular distance, plane-plane distance, offset and slip distance was proposed to discuss the effect of?-?stacking on EPESS properties. In addition, the contributions of?-?stacking on EPESS properties were also evaluated for the other EPESS-active iridium(?) complexes. 3. Effects of sterically hindered spacers towards EPESSNine new iridium(?) complexes, containing different cyclometalated ligands containing bulky groups (tert-butyl or pinene group) and ancillary ligands with different rotational motion, were designed and synthesized.Interestingly, when the?-?interactions were reduced by coexistence of tert-butyl group and pinene segment in cyclometalated ligand, the EPESS properties of iridium(?) complexes were suppressed. However, no significant inhibition of EPESS was observed by reducing intramolecular rotational motion. These facts confirmed that restricted rotational motion was not the origin of EPESS and?-?stacking has great effects on EPESS.