Visible-Light-Induced Carbon-Hydrogen Phosphonylation of Conjugated Polymers via Electron Donor-Acceptor Complex Activation.

Electron donor-acceptor (EDA) complexation has emerged as a sustainable strategy for visible-light-driven reactions. Although numerous EDA-based transformations have been applied to small aromatic molecules, conjugated polymers (CPs) have not yet been explored as substrates for EDA-mediated functionalization. Polymer-based EDA complexes comprise extended π-conjugation systems that reduce exciton-binding energy and facilitate red-shifted absorption, thereby enabling efficient visible-light harvesting. These characteristics are expected to intrinsically promote photoinduced functionalization. Here, we demonstrate the photochemical phosphonylation of poly(9,9-dioctylfluorene) (PFO) induced via the visible-light activation of its EDA complex. Compared with a monomeric model compound, the reaction of PFO proceeded more efficiently, indicating that CPs are promising substrates for EDA-excitation-initiated photochemical transformations. Phosphonylation predominantly proceeded at the 4-position of the fluorene units, thereby preserving the effective π-conjugation length of the polymer backbone. Furthermore, density functional theory calculations revealed that the greater stability of the intermediate species and the lower excitation energy required for 4-position substitution favored that pathway over 3-position substitution. This study establishes a new platform for integrating CPs into EDA-mediated photochemical reactions, offering a facile and sustainable route for the synthesis of versatile functional polymer materials.