Visible‐Light‐Induced Carbon–Hydrogen Phosphonylation of Conjugated Polymers via Electron Donor–Acceptor Complex Activation

Abstract

ABSTRACT 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.