Zincafluorene complex with an empty C-Zn π orbital that captures visible light.

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Materials Science

Background:

• Zinc complexes are cost-effective and non-toxic, making them desirable for photofunctional materials.
• Directly involving zinc orbitals in visible-light interactions within mononuclear systems has been a significant challenge.
• Previous efforts have not fully exploited the potential of zinc's electronic properties for light-driven applications.

Purpose of the Study:

• To engineer mononuclear zinc complexes that engage zinc orbitals in visible-light responses.
• To establish structure-property relationships correlating molecular conformation with photophysical behavior.
• To demonstrate the potential of these complexes in visible-light-driven catalysis.

Main Methods:

• Design and synthesis of novel carbene-zincafluorene frameworks.
• Selective recrystallization to obtain conformational polymorphs.
• Spectroscopic analysis (UV-Vis absorption, photoluminescence), X-ray crystallography, Natural Atomic Orbital (NAO) analysis, and theoretical calculations (including spin-orbit coupling).

Main Results:

• Engineered an empty C-Zn π orbital as the Lowest Unoccupied Molecular Orbital (LUMO) in mononuclear zinc complexes.
• Demonstrated a clear correlation between carbene-zincafluorene coplanarity, LUMO energy, and visible-light absorption.
• Achieved bright room-temperature phosphorescence (21% quantum yield, 2.0 ms lifetime) with significant zinc participation in emission.
• Successfully catalyzed stilbene isomerization using a designed complex under blue-LED irradiation.

Conclusions:

• The study successfully engaged zinc orbitals in visible-light responses by engineering the LUMO in carbene-zincafluorene frameworks.
• Molecular conformation and scaffold tuning are critical for controlling photophysical properties and enhancing zinc's role.
• These findings highlight the non-innocent role of zinc and open avenues for developing novel photoactive mononuclear zinc complexes for catalysis and materials science.