On the design of efficient and versatile photocatalysts promoted by lower-energy light and will contribute to advancing the application of such catalytic processes.

Analogous to natural photosynthesis, which fixes carbon dioxide (CO2) to carbohydrates,
artificial photosynthetic processes, such as CO2-derived solar fuel generation and organic photoredox transformation, are similarly promoted by visible light. Related photocatalysts (PCs) are excited mainly by higher-energy visible photons. For solar energy to be more efficiently utilized, development of molecular PCs which harvest also red/near infrared light will be highly desirable. Meanwhile, the influence of photon’s energy on the excited-state properties of PCs and thus on product selectivity are yet to be understood. Thought red-light driven catalysis for CO2 reduction and redox transformation were explored with different PCs,  analogous NIR-promoted reactions remained uncommon. Recent examples of NIR-promoted photoredox reactions were performed mainly with systems consist of a sensitizer-annihilator pair, and sometimes also a visible-light absorbing photoredox catalyst, via the energy transfer process of triplet-triplet annihilation upconversion (TTA-PUC). However, such TTA-PUC catalytic processes are relatively more complex and often charactered by low upconversion quantum efficiency and small anti-Stokes shift. Their incompatibility with oxygen also seriously limits practical applications. Photoredox catalysis driven by upconversion of red and photons via two-photon absorption (TPA) are explored recently, as it may enhance catalytic efficiency by avoiding the above drawbacks.

It is proposed herein to develop a series of heteroleptic ruthenium isocyano complexes bearing cyclometalating ligands, as a new class of function-integrated PCs for red-/NIR-light promoted CO2 reduction and chromoselective photoredox reactions. The proposed catalyst design shall not only suppress non-productive relaxation pathways of the excited PC, while enabling alternative excitation pathway(s) and catalytic activity via TPA-PUC. Activity of the proposed PCs toward CO2 reduction and atom-transfer reactions will be explored. Photophysical properties and excited states of the PCs, as well as their catalytic properties including chromoselectivity and reaction pathways will be examined by electro- and photochemical methods, and theoretical computation (DFT). In our preliminary studies, a series of dinuclear ruthenium isocyano complexes bearing a rolled-over cyclometalating ligand, namely 6,6'- bis(benzimidazolyl)-2,2'-bipyridine (and its derivative), have been prepared. These complexes exhibit the identical long-lived emissive state when excited with visible and NIR photons respectively. The dinuclear PCs also promote red-/NIR-light driven CO2 reduction and aerobic perfluoroalkylation of amines and alkynes. In the later reaction, different products are selectively formed at different excitation wavelengths (red and NIR photons). Our proposed studies shall shed light on the design of efficient and versatile photocatalysts promoted by lower-energy light and will contribute to advancing the application of such catalytic processes.