Visible Light Harvesting Cr(III) Photocatalysts

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Materials Science

Background:

• Ruthenium(II) and Iridium(III) complexes are widely used as photosensitizers but have limitations.
• Chromium(III) photosensitizers offer long-lived excited states and strong photo-oxidizing properties.
• Poor visible-light absorption is a key challenge for chromium(III) photosensitizers.

Purpose of the Study:

• To enhance the visible-light absorption of pseudo-octahedral chromium(III) photosensitizers.
• To investigate the impact of arylacetylene functionalization on photophysical properties.
• To evaluate the efficiency of these modified chromium(III) complexes in photocatalysis.

Main Methods:

• Synthesis of homoleptic Cr(III) tris(phenanthroline) complexes with arylacetylene units.
• Spectroscopic analysis including UV-Vis absorption and photoluminescence.
• Electrochemical measurements to determine excited-state potentials.
• Photocatalytic experiments for oxidation and cycloaddition reactions.

Main Results:

• Arylacetylene modification induced a significant bathochromic shift (>1 eV) in intraligand transitions.
• Enhanced absorption in UVA and blue-to-green regions (ε ∼25,000-100,000 M-1 cm-1).
• Long excited-state lifetimes (33-119 μs) and strong photo-oxidizing potentials (0.97-1.09 V).
• High quantum yields for singlet oxygen production (ΦΔ ≤ 0.85).
• Efficient photosensitized oxidation and photocatalytic [4 + 2] cycloadditions under visible light.

Conclusions:

• Intraligand transitions in Cr(III) diimines can be leveraged for broad visible-light absorption.
• Arylacetylene functionalization effectively enhances absorption without compromising excited-state properties.
• Modified Cr(III) photosensitizers show great potential for visible-light-driven organic transformations.