Enabling high-mobility, ambipolar charge-transport in a DPP-benzotriazole copolymer by side-chain engineering

In this article we discuss the synthesis of four new low band-gap co-polymers based on the diketopyrrolopyrrole (DPP) and benzotriazole (BTZ) monomer unit.


TGA and DSC
Thermogravimetric analyses (TGA) were performed on a NETZSCH TG 209 F3 thermogravimetric analyzer at a heating rate of 10 °C min-1 under a N2 atmosphere.
Thermal transition behaviours of polymers were measured on a NETZSCH DSC 404 F1 modulated differential scanning calorimeter (DSC) at a heat/cool rate of 10 °C min-1 under N2 for three heat/cool cycles.
No appreciable glass transitions were detected in any of the polymers.

Cyclic voltammetry (CV) experiments for (l-C18)-DPP-(b-C17)-BTZ and (l-C18)-DPP-(l-
C8)-BTZ were performed at a sweep rate of 50 mV/s. CVs were carried out in a threeelectrode cell consisting of a glassy carbon working electrode, a platinum wire auxiliary electrode, and a Ag/Ag+ pseudo-reference electrode. The supporting electrolyte was 0.10 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) in CH3CN. The solutions were deoxygenated by sparging with argon prior to each scan and blanketed with argon during the scans. The glassy carbon working electrode was prepared by polishing with 5 μm alumina and washed and dried before the polymer was drop-casted on the electrode from chlorobenzene solution to form a film. Ferrocene/ferrocenium redox couple was used as the internal standard.
The HOMO energy level was calculated from the onset of the oxidation potential of the polymer using the following: EHOMO = -(4.8 + Eox onset) eV. Note that E LUMO is calculated from E HOMO and the optical band gap. The reduction onset values should not be used to estimate E LUMO as the CV of the reduction process was not reversible.