Enhanced Spin-Forbidden Excitation of Ru(II) Polypyridyl Complexes for the Promotion of Red-Light Photocatalysis
Year: 2026
Type: preprint
Abstract: Photoredox catalysis, mainly occurring under blue light, has emerged as an indispensable tool in modern organic synthesis. However, some limitations remain, mostly due to the high energy inherent to the irradiation wavelengths used. Red-light excitation of transition-metal photocatalysts is attractive for expanding the synthetic utility of visible-light photochemistry. Here, we report a strategy to enhance spin-forbidden red-light absorption in Ru(II) polypyridyl complexes through ligand tuning. [Ru(Br2-bpy)3](PF6)2 exhibits a substantially intensified spin-forbidden absorption band in the red region, with a molar extinction coefficient approximately 10-fold higher than that of [Ru(bpy)3]2+. The enhanced red-light absorption results in markedly improved photocatalytic activity under 660 nm irradiation in a range of electron- and energy-transfer transformations. Comparison with the parent complex demonstrates that modulation of the spin-forbidden absorption pathway can directly influence red-light photochemical reactivity. These findings support ligand modification as an effective approach for enhancing spin-forbidden excitation and provide a molecular design strategy for redlight-responsive Ru(II) photocatalysts, establishing Ru(II) polypyridyl complexes as an efficient family of photocatalysts activated via a spin-forbidden transition pathway.
Source: ChemRxiv
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221518683