Rationalizing Photophysics of Co(III) Complexes with Pendant Pyrene Moieties

Area of Science:

• Photochemistry and Photophysics
• Coordination Chemistry
• Materials Science

Background:

• Pendant organic chromophores enhance metal-based photosensitizers by increasing π conjugation and lowering absorption bands.
• Understanding excited state dynamics is crucial for optimizing photocatalytic performance.

Purpose of the Study:

• To rationalize the excited state dynamics of a Cobalt(III) complex with pendant pyrene moieties (CoL).

Main Methods:

• Spectroscopic studies (UV-Vis absorption, luminescence spectroscopy).
• Computational modeling.
• Transient absorption spectroscopy.

Main Results:

• The Co(III) complex with pyrene (CoL) shows higher visible absorptivity and blue luminescence compared to the complex without pyrene.
• Excited states exhibit a mix of singlet intraligand charge-transfer (¹ILCT) and ligand-to-metal charge-transfer (¹LMCT) character.
• Triplet metal-centered (³MC) states dominate the decay pathway with a 2.4 ps lifetime, showing no photoactivity for singlet oxygen formation or triplet-triplet energy transfer (TTET).

Conclusions:

• The metal center significantly influences emissive properties and excited-state decay pathways.
• Pendant pyrene moieties enhance visible light absorption and luminescence but do not lead to efficient triplet state population for photocatalysis.
• Triplet metal-centered states are the primary deactivation pathway, limiting photocatalytic applications.