The Metamorphosis of Strongly Electron‐Accepting Dithieno[2,3‐ b ;3′,2′‐ e ]‐4‐Keto‐1,4‐Dihydrophosphinines

The development of multifunctional organic π ‐conjugated molecules has been of great interest due to their potential use in sustainable energy applications. Some progress has been made in the development of n‐type, electron‐acceptor molecules with very low LUMO levels, but the diversity of suitable molecular scaffolds remains strictly limited. Along similar lines, phosphorus incorporation into ring‐fused organic scaffolds has proven to create molecules with beneficial optical and electrochemical properties and electron‐acceptor character, as well as exceptional tunability. Herein, we report a detailed structure–property study of the dithieno[2,3‐ b ;3′,2′‐ e ]‐4‐keto‐1,4‐dihydrophosphinine system, an intriguing scaffold that has remained largely unexplored to date. Through various targeted approaches, we comprehensively explore a series of dithienoketophosphinine‐based electron‐acceptor species functionalized at the phosphorus center, the carbonyl group, and the thieno‐backbone to explore and more deeply understand the impact on the electrochemical, optical, and structural properties of the system. Our study convincingly establishes the superior electron‐acceptor properties of the scaffold that outcompete state‐of‐the‐art materials, as well as its high degree of tunability that also unlocks valuable emission features upon extension of the core.