Electronic Supplementary Information (ESI) AIE-active Ir(III) Complexes Functionalized with a Cationic Schiff Base Ligand: Synthesis, Photophysical Properties and Their Applications in Photodynamic Therapy

Photodynamic therapy (PDT) is a promising cancer treatment method. Traditional small-molecule photosensitizers (PSs) suffer from low intersystem crossing (ISC) ability and aggregation-caused quenching (ACQ), which adversely affects the luminous efficiency and singlet oxygen (1O2) yield of PSs in the aggregated state. Ir(III) complexes are promising PSs with long excited-state lifetime, good photophysical and photochemical properties and large Stokes shifts. Aggregation-induced emission (AIE) characteristics could reduce the nonradiative recombination and improve the ISC ability of excited states through the restriction of the intramolecular motions in aggregated states. Accordingly, two AIE-active Ir(III) complexes Ir-1-N+ and Ir-2-N+ were successfully designed and obtained based on Schiff base ligands. Experimental results showed that Ir-1-N+ and Ir-2-N+ have good photophysical properties and the corresponding nanoparticles (NPs) have good water solubility and 1O2 generation ability. Notably, Ir-2-N+ NPs can be efficiently taken up by mouse breast cancer cells (4T1 cells) with good biocompatibility, low dark toxicity and excellent phototoxicity. This work demonstrates a versatile strategy for exploiting efficient transition metal PSs with a cationic ligand in PDT.

The auxiliary ligand L2 was synthesized by a Schiff base reaction. A mixture of aminochalcone (0.088 g, 0.3 mmol) and o-hydroxybenzaldehyde (0.108 g, 0.9 mmol) in ethanol (30 mL) was refluxed with stirring for 8 h to give an orange precipitate. The reaction mixture was cooled to room temperature. The precipitate was filtered to obtain ligand L2.

Synthesis of the Cyclometallating ligand
Scheme S3. Synthetic route for the cyclometallating ligand.
1-Chloroisoquinoline (0.496 g, 3.06 mmol) and 4-triphenylamine boronic acid (0.972 g, 3.36 mmol) were dissolved in toluene (30 mL) and tetrakis(triphenylphosphine)palladium(0) (0.177 g, 0.15 mmol) was added as a catalyst. Sodium carbonate (20 mL of 2 mol L -1 solution) was added and the mixture was refluxed for 48 h under N2. The mixture was then left to cool and extracted with dichloromethane. The organic phase was separated, dried over anhydrous MgSO4 and evaporated. The crude product was purified by silica gel column chromatography (dichloromethane/petroleum ether, 10/3 v/v

Synthesis of dichloro-bridged diiridium complex
Scheme S4. Synthetic route for the dichloro-bridged diiridium complex.

Synthesis of Ir-1-N +
The complex Ir-1-N (0.0450 g, 0.05 mmol) and acetonitrile were mixed under nitrogen atmosphere. Iodomethane (1 mL) was added dropwise and the mixture was heated for 12 h.