A π-conjugated, covalent phosphinine framework

Structural modularity of polymer frameworks is a key advantage of covalent organic polymers, however, only C, N, O, Si and S have found their way into their building blocks so far. Here, we expand the toolbox available to polymer and materials chemists by one additional nonmetal, phosphorus. Starting with a building block that contains a λ⁵-phosphinine (C₅P) moiety, we evaluate a number of polymerisation protocols, finally obtaining a π-conjugated, covalent phosphinine-based framework (CPF-1) via Suzuki-Miyaura coupling. CPF-1 is a weakly porous polymer glass (72.4 m² g^-1 N₂ BET at 77 K) with green fluorescence (λ_max 546 nm) and extremely high thermal stability. The polymer catalyzes hydrogen evolution from water under UV and visible light irradiation without the need for additional co-catalyst at a rate of 33.3 μmol h^-1 g^-1. Our results demonstrate for the first time the incorporation of the phosphinine motif into a complex polymer framework. Phosphinine-based frameworks show promising electronic and optical properties that might spark future interest in their applications in light-emitting devices and heterogeneous catalysis.