Self-assembled J-aggregation of AIE-active iridium complexes regulated by hydrogen bond between ligand and solvent

Abstract

How to precisely regulate the aggregates of nonplanar iridium complexes is unclear, and its mechanism is rarely reported, especially in solution. Herein, two iridium complexes (Ir-1 and Ir-2) containing aldehyde-substituents and different auxiliary ligands are reported. In MeOH/H₂O mixed solution, Ir-1 showed aggregation-induced emission (AIE) while Ir-2 showed aggregation-caused quenching. The polarity of MeOH/H₂O solvent and the self-assembled J-aggregation of the complexes are a pair of competitive factors affecting the luminescence intensity. The results show that the self-assembled J-aggregates in Ir-1 solution contain many nanotoroids with smaller size and larger Zeta potential, and that in Ir-2 solution have regular nanocubes with larger size and smaller Zeta potential. The molecular structure and Zeta potential play a significant role in the self-assembled morphology of nanoaggregates. With the addition of D₂O in MeOD/D₂O solvent, the proton signal of aldehyde-groups and ligands of the complexes displayed marked changes in ¹H NMR spectra, indicating that the hydrogen couplings among MeOH/H₂O, aldehyde-groups and ligands can synergistically regulate the self-assembled morphology. Based on the AIE property, we further monitored the promoting effects of aldehyde-groups and ligand on the self-assembly. That is, the addition of MeONa or AcOH caused the luminescence to turn on and off in the complex solution, respectively, suggesting that the aldehyde-groups, the auxiliary ligand and the solvent indeed promote the formation of the self-assembled J-aggregates before the addition of ions to disrupt the solution. This work provides is a rare example for regulating the self-assembled J-aggregates of AIE iridium complex.