Excited State Dynamics of a Conformationally Fluxional Copper Coordination Complex

Area of Science:

• * Materials Science
• * Photochemistry
• * Renewable Energy

Background:

• * Solar energy conversion to chemical fuel is crucial for sustainable energy.
• * A key challenge is the mismatch between fast light absorption and slower chemical reaction timescales.
• * This limits the efficiency of solar-to-fuels technologies.

Purpose of the Study:

• * To design and synthesize earth-abundant coordination complexes for efficient solar energy conversion.
• * To address the timescale mismatch in solar-to-fuels processes using conformationally dynamic ligands.
• * To develop materials that accelerate charge separation (CS) and decelerate charge recombination (CR).

Main Methods:

• * Synthesis and characterization of novel copper coordination complexes with twisted intramolecular charge transfer (TICT) ligands.
• * Spectroscopic studies (UV-Vis, emission) to analyze ground and excited states.
• * Time-resolved spectroscopy (emission, transient absorption) to probe excited-state dynamics.
• * Time-dependent density functional theory (TDDFT) for electronic structure and excited-state geometry analysis.

Main Results:

• * New copper complexes exhibit oxidation state-dependent conformational dynamics.
• * Improved ligand design simplifies photophysics, suppressing unwanted ligand-centered excited states.
• * TDDFT reveals a rare metal-to-TICT electronic transition and supports transient Cu(II) charge-separated species formation.
• * Established a model for excited-state dynamics in these proof-of-concept systems.

Conclusions:

• * Conformationally fluxional copper complexes show promise for solar-to-fuels applications.
• * Ligand design is critical for controlling excited-state dynamics and achieving efficient charge separation.
• * Photoinduced conformational gating offers a viable strategy for long-lived charge-separated states.