Photoredox-active Dyads Based on a Ru(II) Photosensitizer Equipped with Electron Donor or Acceptor Polymer Chains: A Spectroscopic Study of Light-Induced Processes toward Efficient Charge Separation

A photosensitizer–multielectron-acceptor dyad (P–An) was synthesized via controlled nitroxide-mediated polymerization of styrenic naphthalene diimide (NDI) and subsequent functionalization with a [Ru(dqp)2] 2+ photosensitizer (dqp is 2,6-di(quinolin-8-yl)pyridine) at the chain terminus. The optical and electrochemical analysis showed the preserved properties of the individual subunits, corroborated by the analysis of the related multi–electron donor assembly (Dn–P) based on triarylamine (TARA). A detailed photophysical study of both dyads is presented to elucidate the primary light-induced energy and electron transfer events. While the Dn–P dyad displays the unchanged 3MLCT-based (MLCT is metal-to-ligand-charge transfer) emission of the pristine photosensitizer, the P–An system revealed efficient emission quenching and the occurrence of the NDI radical anion signature. The time-resolved emission data revealed a non-monoexponential decay attributed to the conformational freedom by the flexible linkage, while the transient absorption data confirmed the rapid formation of the reduced acceptor.