From Molecular to Polymeric Donors: Prolonged Charge Separation in Modular Photoredox-Active Ru(II) Polypyridyl-Type Triads

In this contribution, the divergent modular synthesis of photoredox-active dyads, triads and a tetrad descending from one ligand precursor is presented by combining "chemistry-on-the-ligand", stepwise complexation and "chemistry-on-the-complex" with minimal synthetic efforts. In the final step, Pd-mediated borylation and subsequent Suzuki-Miyaura cross-coupling was employed to introduce the different (multi)donor moieties at the preassembled P-A dyad subunit. The (spectro-)electrochemical data revealed preserved redox properties of the subunits and minimal driving force for oxidative quenching by the naphthalene diimide-based (NDI) acceptor and, thus, high-energy charge separated (CS) states. Time-resolved transient absorption and emission data revealed the formation of long-lived CS states in the polymer-based triads, i.e., the CS lifetime is extended by 2 orders of magnitude in comparison to the molecular triad. The long-lived CS state (13.2 μs) of the conjugated polycarbazole (Carb_n) multidonor demonstrates that the rational modular design and efficient synthesis of advanced photoredox-active assemblies can be readily achieved by late-stage diversification utilizing the "chemistry-on-the-complex" approach.