Design and Synthesis of an Indoloquinoxaline Non-Fullerene Acceptor-Polythiophene Donor-Based Double Cable Polymer as an All-Organic Photocatalyst for Artificial Photosynthesis of H2O2.

Abstract

Excitons produced upon photoexcitation of organic semiconducting polymers (OSPs) are short lived, which limits their performance as photoactive materials. Exciton dissociation in OSPs can be enhanced by covalently conjugating them with acceptor species displaying higher electron affinity in a double cable polymer (DCP) arrangement, where non-fullerene acceptors (NFAs) are emerging as attractive alternatives. Herein, we report a new all-organic DCP comprising an electron donor polythiophene (PTh) covalently conjugated to an indoloquinoxaline (IQx) NFA (PTh-IQx-DCP). The selection of PTh and IQx as donor-acceptor pair is supported by the experimentally and theoretically determined favorable alignment of their band gaps and energies of HOMOs/LUMOs. The fluorescence and TRPL profiles reveal enhanced donor-acceptor electronic communication in PTh-IQx-DCP. PTh-IQx-DCP exhibits superior photoelectrochemical characteristics compared to P3HT, IQx, and P3HT+IQx physical hybrid (PH). As photocatalyst, PTh-IQx-DCP produces 906 ± 38 µM.mg^-1 H₂O₂ cumulated over 10 photocatalytic cycles with a 10-cycles apparent average turnover frequency (TOF) of 3.5 h^-1 and an apparent quantum yield (AQY) of 0.8% at 440 nm. The H₂O₂ production for PTh-IQx-DCP averaged over 10 photocatalytic cycles is 1.6, 3.4, and 1.4 times superior compared to P3HT, IQx, and P3HT+IQx PH, respectively. Overall, this work expands the molecular design space of DCPs based photoactive materials.