Stabilizing the excited states of organic phosphorescent photosensitizers via self-assembly for CO₂ photoreduction

The development of pure organic photosensitizers remains challenging due to the low intersystem crossing efficiency and the instability of triplet excitons. Herein, fused-ring phosphorescent molecules enhance visible-light absorption, with heteroatom-rich structures breaking the restriction of low triplet excitons. A derivative, 2,3,5,6,9,10-hexabutoxy-8-phenyldithieno-tribenzo-pyridine (TPy), exhibits high ISC efficiency and efficiently sensitizes Fe-catalysts for CO₂ photoreduction to CO. We further developed a self-assembly method to stabilize triplet excitons by embedding TPy within the rigid core of amphiphilic polymer nanoparticles. The hydrophobic core of the nanoparticles significantly prolongs the excited-state lifetime, while the hydrophilic shell ensures excellent dispersibility and stability. This system achieves a turnover number of 2041 and retains 93.5% of its initial activity after three cycles. Our work provides a general strategy for designing stable and highly efficient organic photosensitizers, paving the way for sustainable photoredox catalysis.