Immobilization and practical photoredox processes with dithienoquinoxaline

Abstract

A novel organic dithienoquinoxaline photoredox catalyst has been immobilized through a straightforward copolymerization approach. The performed heterogenization did not alter fundamental thermal, electrochemical, and optical properties and, most importantly, the ability of the excited catalyst to act either as a one-electron reductant or oxidant using a single light source (similar to 450 nm). The oxidation power of the triplet excited state of both homogeneous and heterogeneous photocatalysts has been demonstrated in the oxidation of sulphides, amines, and alcohols. The photoreduction of nitroaromatics and ketones has been accomplished by utilizing (double-excited) dithienoquinoxaline radical anion. Both oxidation and reduction reactions were accomplished either in batch (homo/heterogeneous) or under continuous-flow conditions using a porous flexible monolithic column with immobilized catalyst. Repetitive cyclic oxidation/reduction of pharmaceutically and industrially important fluorenol/one system along with a consecutive nitro reduction and sulphur oxidation in bis(4-nitrophenyl)sulphide towards an antimalarial agent further demonstrates the wide applicability of the developed catalytic systems/protocols. The recyclability and eventual structural changes of the immobilized catalyst have been addressed through FT-IR spectra and TON/TOF values.