Tuning the Photocatalytic CO₂ Reduction through para-Substituents in Bipyridyl Rhenium Complexes

Area of Science:

• Inorganic Chemistry
• Photocatalysis
• Sustainable Chemistry

Background:

• Developing efficient photocatalysts for CO2 reduction is crucial for sustainable energy solutions.
• Rhenium polypyridyl complexes are promising candidates for CO2 photoreduction.

Purpose of the Study:

• To investigate the impact of ligand substituents on the photocatalytic activity of fac-[Re(NN)(CO)3Cl] complexes for CO2 to CO reduction.
• To correlate structure-activity relationships with electronic and steric effects of substituents.

Main Methods:

• Synthesis and characterization of six fac-[Re(NN)(CO)3Cl] complexes with varied 2,2'-bipyridine ligands.
• Photocatalytic CO2 reduction experiments using sacrificial electron donors.
• Spectroscopic and electrochemical studies to analyze light absorption, redox potentials, and excited-state dynamics.

Main Results:

• Electron-donating groups enhanced the reactivity of the one-electron-reduced species (OERS) with CO2 but slowed excited-state quenching.
• Electron-withdrawing groups improved reductive quenching but decreased OERS reactivity.
• Hammett constants (σp) effectively correlated substituent effects with photocatalytic performance.

Conclusions:

• Photocatalytic CO2 reduction efficiency is tunable by strategic modification of the bipyridine ligand.
• Balancing excited-state dynamics and OERS reactivity is key for optimizing photocatalyst design.
• Understanding substituent effects allows for rational design of improved rhenium-based photocatalysts.