Dithioketopyrrolopyrrole (DTPP)-based conjugated polymers prepared upon thionation with Lawesson's reagent

Three dithioketopyrrolo[3,4-c]pyrrole (DTPP)-based polymers TP1–TP3 were prepared upon thionation of diketopyrrolo[3,4-c]pyrrole (DPP)-based conjugated polymers P1–P3 with Lawesson's reagent (LR, 2,4-bis-(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide) in p-xylene in high yield. P1–P3 were previously synthesized from 1,4-diketo-3,6-bis(4-bromophenyl)-2,5-bis(2-hexyldecyl)pyrrolo[3,4-c]pyrrole and 2,5-bis-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophene (P1), 1,4-diketo-3,6-di(4-bromophenyl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole and 9-(2-ethylhexyl)-2,7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-carbazole (P2), and 1,4-diketo-3,6-di(4-bromothienyl)-2,5-bis(2-hexyldecyl)pyrrolo[3,4-c]pyrrole and 2,5-bis-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophene (P3) using Pd-catalyzed Suzuki coupling. DTPP-based polymers are well soluble in common organic solvents forming dark green solutions. Compared with the starting polymers the absorption maxima of TP1–TP3 in solution are red-shifted by more than 100 nm. Optical bandgaps are at about 1.8 eV for diphenyl-DTPP-based polymers TP1 and TP2, and at 1.3 eV for dithienyl-DTPP-polymer TP3. Cyclovoltammetric studies indicate quasireversible oxidation behavior and irreversible reduction behavior. The solid polymers are stable against photoirradiation, while solutions of TP1 and TP2 undergo rapid photode-composition. In contrast, the photostability of TP3 is much higher.