Switched fluorescence and photosensitization based on reversible ion-pairing

Area of Science:

• Photochemistry
• Organometallic Chemistry
• Materials Science

Background:

• Iridium complexes are widely studied for their photophysical properties.
• Ion-pair formation and solvent effects can significantly influence excited-state dynamics.
• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.

Purpose of the Study:

• To investigate the role of ion association in the photophysical behavior of an iridium complex.
• To understand how excitation energy is channeled upon controlling ion pairing.
• To explore the impact of NHC ligand donation strength on photosensitizing efficiency.

Main Methods:

• Synthesis and characterization of the iridium complex [Ir(bdpSO3)(cod)(IMes)].
• Photophysical studies including fluorescence and triplet state measurements.
• Varying solvent conditions to control ion-pair association.

Main Results:

• The close ion-pair exhibited efficient photosensitization, while the solvent-separated anion was highly fluorescent.
• Ion association controlled the excitation energy pathway, favoring either fluorescence (S1 state) or intersystem crossing (T1 state for 1O2 generation).
• Electron-rich NHC ligands were found to be essential for highly efficient photosensitizers.

Conclusions:

• Precise control over ion association in iridium complexes is a key strategy to tune photophysical properties.
• This control allows for selective channeling of excitation energy towards fluorescence or photosensitization.
• The electronic properties of NHC ligands are critical for optimizing photosensitizer performance.