Aggregation Induced Emission (AIE) Properties of Heteroleptic Ir^III 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 1phenypyrazole (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.[a] M.

Aggregation induced emission of chalcones

“…Organic luminophores can display either (i) aggregation caused quenching (ACQ), wherein typical fluorophores emit intensely in dilute solutions, but do not show fluorescence or are weakly fluorescent in their solid state, or (ii) aggregation-induced emission (AIE), where the fluorophores emit effectively in the condensed state, but their solutions have poor or quenched emissions (Luo et al 2001). However, the intermolecular interactions in organic planar small molecules and the π-π stacking effect of aromatic rings, which "turns off" the emission of ACQ molecules in solid state is a limiting factor for many practical applications (Prajapati and Surati 2019). Nevertheless, the presence of aromatic rings, bulkier substituent groups or quaternary centers and hydrogen bonding can hamper ππ cofacial stacking to avoid ACQ, specifically in H-aggregates that are highly emissive (Espitia Cogollo et al 2020).…”