Bis-cyclometalated Ir(III) complexes as efficient singlet oxygen sensitizers

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Materials Science

Background:

• Bis-cyclometalated Iridium(III) complexes are investigated for their photophysical properties.
• Singlet oxygen sensitization is a key mechanism in photodynamic therapy and photocatalysis.
• Understanding the relationship between complex structure and singlet oxygen generation is crucial for developing efficient photosensitizers.

Purpose of the Study:

• To investigate the singlet oxygen sensitization properties of a series of bis-cyclometalated Iridium(III) complexes.
• To evaluate the influence of ancillary ligands (acetylacetonate, glycine, pyridine) on singlet oxygen quantum yields and quenching rates.
• To explore the excitation pathways (ligand-based vs. lowest energy excited state) affecting singlet oxygen generation.

Main Methods:

• Synthesis of bis-cyclometalated Iridium(III) complexes with varying ancillary ligands: (bt)2Ir(acac), (bsn)2Ir(acac), (pq)2Ir(acac), (bsn)2Ir(gly), and (bt)2Ir(py)Cl.
• Measurement of singlet oxygen quantum yields (PhiDelta) using spectroscopic techniques.
• Determination of singlet oxygen quenching rates for the synthesized complexes.

Main Results:

• Complexes with acetylacetonate ancillary ligands demonstrated high singlet oxygen quantum yields (PhiDelta = 0.7-1.0 +/- 0.1).
• Singlet oxygen quantum yields remained high regardless of the excitation state (ligand-based or MLCT + 3LC).
• The glycine and pyridine tethered derivatives also exhibited high singlet oxygen yields (PhiDelta = 0.7-1.0 +/- 0.1).
• Singlet oxygen quenching rates for beta-diketonate complexes were relatively slow [(5 +/- 2) x 10^5 to (6 +/- 0.2) x 10^6 M^-1 s^-1].

Conclusions:

• Bis-cyclometalated Iridium(III) complexes, particularly those with acetylacetonate, glycine, and pyridine ligands, are highly efficient singlet oxygen sensitizers.
• The observed high singlet oxygen quantum yields suggest significant potential for these complexes in applications requiring singlet oxygen generation, such as photodynamic therapy.
• The study provides valuable insights into the structure-property relationships governing singlet oxygen sensitization in iridium complexes.