Spectroscopic characterization of charge carriers of the organic semiconductor quinacridone compared with pentacene during redox reactions

In recent research, the pigment quinacridone, a hydrogen-bonded organic semiconductor, has gained attention in electronic device and catalysis applications due to its extraordinary stability. In this work, we combine electrochemistry with spectroscopy ranging from UV-VIS to mid-IR, allowing a deeper understanding and also structural analysis of the redox products. This is important for materials used in bioelectronic applications, such as quinacridone which is a promising candidate. Several absorption bands related to sub-gap transitions appear upon redox reactions in this spectral range. Optical experiments are correlated with electron paramagnetic resonance measurements, proving the formation of different kinds of charge carriers. The results are discussed and compared with those for the all-carbon five-ring analogous molecule pentacene, because both pigments are candidates for ambipolar organic field-effect transistors, showing similar charge carrier mobilities. In the case of quinacridone, the charged species created upon redox reactions are more localized on different functional groups in the heteroatomic structure than in pentacene.