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 multielectron donor assembly (D-n-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 D-n-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 nonmonoexponential decay attributed to the conformational freedom by the flexible linkage, while the transient absorption data confirmed the rapid formation of the reduced acceptor.