Modulating the Excited-State Decay Pathways of Cu(I) 4H-Imidazolate Complexes by Excitation Wavelength and Ligand...

Area of Science:

• Photochemistry
• Materials Science
• Coordination Chemistry

Background:

• Copper(I) 4H-imidazolato complexes are earth-abundant photosensitizers with potential in artificial photosynthesis.
• Their broad light absorption and redox accumulation capabilities make them attractive for energy applications.

Purpose of the Study:

• To systematically investigate the excited-state relaxation dynamics of novel heteroleptic Cu(I) 4H-imidazolato complexes.
• To understand the influence of phenyl, tolyl, and mesityl side groups on photophysical processes.

Main Methods:

• Femtosecond and nanosecond time-resolved transient absorption spectroscopy.
• Theoretical calculations.
• Steady-state absorption spectroscopy and spectroelectrochemistry.

Main Results:

• Fast intersystem crossing (0.6-1.2 ps) to the triplet metal-to-ligand charge transfer (MLCT) manifold was observed.
• Triplet-state relaxation occurs via N-aryl ring planarization.
• Singlet state relaxation involves two distinct geometries (S1/2,relax and S3/4,relax) with ground-state recovery and internal conversion on a 100 ps timescale.
• Photophysical processes are dictated by ligand steric hindrance and excitation wavelength.

Conclusions:

• The steric hindrance of side groups significantly impacts the photophysical properties of these copper complexes.
• Excited singlet-state pathways are tunable by excitation wavelength, offering control over photochemical processes.