Bidirectional sensitization in Ruthenium(II)-antenna dyad beyond energy flow of biological model for efficient photosynthesis

In natural photosynthetic system, sunlight is harvested by chlorophyll, subsequent funneling of the excitation energy to redox centers to trigger redox reaction. In contrast, the functions of light absorption, intersystem crossing and redox reaction were integrated into a single species (i.e. Ru(bpy)₃²⁺) in traditional catalytic system. Inspired by nature, we explore a strategy to introduce the strong absorbing dyes into Ru redox center and regulate their excited states by increasing the π-conjugation of dyes to afford a series of Ru(II) complexes-chromophore dyads (Ru-1 – Ru-5). Experimental and theoretical investigations reveal a forward singlet energy transfer following a backward triplet energy transfer between chromophore/Ru center in Ru-5, presenting a bidirectional sensitization, which not only achieve the functional separation among components in photosensitizer but also promote the efficient collaboration between Ru(II) center and chromophore. Remarkably, Ru-5 exhibited a strong visible light absorption at 463 nm (ε = 50500 M⁻¹cm⁻¹) and its triplet lifetime reached to 122.5 μs, over 400 times longer than the single component complex Ru-1. These advantages enable Ru-5 a significantly higher catalytic activity than the typical Ru(bpy)₃²⁺ for both energy- and electron-transfer reactions. This work opens up a new avenue to improve photosensitization for efficient photosynthesis by learning from nature.