Panchromatic Photocatalysis using a Ruthenium Polypyridyl Complex

Abstract

Photocatalysis has reshaped synthetic chemistry and materials science by enabling various transformations under mild conditions using light as a traceless reagent. However, most molecular photocatalysts/photosensitizers only operate within a narrow blue-to-green window, which imposes practical limitations, such as shallow light penetration, competing absorption by substrates and additives, and incompatibility with light-sensitive functionalities. Extending the activity of photocatalysis into the deep-red and near-infrared (NIR) regions offers a compelling solution. However, the lower energy of red and NIR photons typically leads to weakly reactive or short-lived excited states, limiting their photocatalytic capability. A general strategy that enables a single molecular chromophore to function across a broad spectral range remains elusive. Herein we report a molecular engineering strategy that renders multiple excitation pathways generating the same reactive excited state within one ruthenium complex. By incorporating extended π-conjugation into a ruthenium polypyridyl framework, the complex can be activated through one-photon excitation in the short-wavelength visible region, weak direct excitation of the lowest metal-to-ligand charge transfer manifold in the deep red, and two-photon absorption under NIR light irradiation up to 850 nm. Spectroscopic and kinetic analyses demonstrate that distinct wavelength-dependent excitation modes populate a common long-lived MLCT excited state, preserving photocatalytic performance across the UV–vis–NIR spectral window. This wavelength-adaptive behavior enables diverse organic transformations and polymerization processes under conditions inaccessible to conventional photocatalysts. More broadly, this work illustrates how rational ligand design can make multiple excitation modes converge on one reactive state, offering a practical route to ruthenium photocatalysts that operate across the visible-to-NIR range.