Charge Storage and Dark Photocatalysis in Multivariate Ti-Based Metal-Organic Frameworks

"Dark photocatalysis" decouples electron storage from photoconversion, offering a promising route to buffer solar intermittency, however requiring precise control of light-matter interactions. Metal-organic frameworks (MOFs) provide a platform to tailor these interactions at the molecular level through judicious selection of organic linkers and interconnected metal nodes. This study advances design principles for dark photocatalysis by integrating two linkers with complementary light-interaction roles in a multivariate (MTV) COK-47 series. Varying the ratio between biphenyl dicarboxylate (biph) and bipyridine dicarboxylate (bipy) linker shows that under continuous irradiation (365 nm), COK-47_biph is the most photocatalytically active member, surpassing COK-47_bipy by threefold. In contrast, COK-47_bipy exhibits an eightfold increase in photocharging capacity, revealed by a multispectroscopic approach, evidencing the formation of Ti³⁺ and reduced linker species as storage unit. The stored charges drive methyl viologen (MV) reduction and H₂ evolution in the dark. Notably, the mixed-linker material COK-47_50-50 combines both advantages, delivering near-maximal H₂ production under illumination while retaining substantial charge storage capability, achieving the highest MV reduction activity and second-highest dark H₂ evolution in the series. These findings connect framework composition to light-matter interaction, charge storage capacity, catalytic activity, and establish a design strategy for multifunctional dark photocatalytic materials.