Diketopyrrolopyrrole based molecular semiconductors with intrinsic conductivity

Intrinsically conducting diketopyrrolopyrrole (DPP) compounds functionalised with pendant quaternary ammonium groups have been synthesised. The hydroxide forms were found to be the product of base hydrolysis of the DPP amide during synthesis, likely made possible by restricted resonance. This gave mixed chemical compositions of solutions and conductive films formed by drop-casting. Chemical decomposition of the hydrolysed compounds was also observed at temperatures above 85 °C. Conductivities of approximately 3 × 10⁻⁴ S m⁻¹ were observed in processed films of DPP ammonium hydroxides. It was also found that trifluoroacetic acid (TFA) DPP precursors gave clear electron paramagnetic resonance (EPR) signals indicative of doping and exhibited conductivities one order of magnitude larger than the hydroxides. This opens the possibility of using ammonium TFAs as moieties for doping organic semiconductors.