Aggregation Induced Emission (AIE) Properties of Heteroleptic IrIII Complexes With Non‐chromophoric Ligand Effect: Synthesis, Characterization and Photophysical Investigations

Abstract Three bis‐cyclometalated iridium(III) complexes (1‐3) [Ir(ppz) 2 (L 1 )] (1) , [Ir(ppz) 2 (L 2 )] (2) and [Ir(ppz) 2 (L 3 )] (3) , containing 1‐phenypyrazole (ppz) as the cyclometalated ligands and pyrazolone based derivatives as ancillary ligands (L 1 ‐L 3 ) were synthesized and characterized by spectroscopic techniques. All the complexes show strong photoluminescence in the range of 517‐521 nm in solid state at room temperature. However, it does not show luminescence in solution state due to ‘Aggregation Induced Emission’ (AIE). Photophysical and electrochemical properties were performed to understand and evaluate the AIE behavior of designed complexes on the basis of structural properties relationship with other reported iridium complexes. The designed complexes show good Φ PL in the range of 0.18‐0.21 in solid state due to non‐chromophoric schiff base ligands lower the energy of the triplet state to such a value that the non‐radiative (NR) state is no longer thermally accessible at room temperature. The ancillary ligands also tune the HOMO and LUMO level, where the decreases LUMO mainly influence by substitution effect of phenyl ring of Schiff base ligands and subsequently it makes the excited state far from the non‐radiative states, leading to enhance the efficiency even at room temperature with the bandgap (E g ) in the range of 2.63‐2.65 eV. All the designed complexes are thermally stable upto 300 °C.