In this work, we focus on the formation of different kinds of charge carriers such as polarons and bipolarons upon p-type doping (oxidation) of the organic semiconductor poly(3- hexylthiophene-2,5-diyl) (P3HT). We elucidate the cyclic voltammogram during oxidation of this polymer and present spectroscopic changes upon doping in the UV/Vis/near-IR range as well as in the mid-IR range. In the low-oxidation regime, two absorption bands related to sub-gap transitions appear, one in the UV/Vis range and another one in the mid-IR range. The UV/Vis absorption gradually decreases upon further doping while the mid-IR absorption shifts to lower energy. Additionally, electron paramagnetic resonance (EPR) measurements are performed, showing an increase of the EPR signal up to a certain doping level, which significantly decreases upon further doping. Furthermore, the absorption spectra in the UV/Vis range are analyzed in relation to the morphology (crystalline vs. amorphous) by using theoretical models. Finally, the calculated charge carriers from cyclic voltammogram are linked together with optical transitions as well as with the EPR signals upon p-type doping. We stress that our results indicate the formation of polarons at low doping levels and the existence of bipolarons at high doping levels. The presented spectroscopic data are an experimental evidence of the formation of bipolarons in P3HT.

The electrocatalytic reduction of CO2 to methanol is explored by the direct comparison of protonated pyridazine and pyridine for their capabilities towards CO2 reduction. The two materials inherit a significant difference in their pKa values adding valuable information to the ongoing discussion on the nature of CO2 reduction catalyzed by pyridinium and similar nitrogen containing heteroaromatic systems. Cyclic voltammetry studies as well as bulk controlled‐potential electrolysis experiments were performed combined with product analysis using gas chromatography. Methanol was detected as main CO2 reduction product in all cases.

The front cover artwork is provided by Dr. Christina Enengl, Dr. Sandra Enengl and Dr. Helmut Neugebauer (Johannes Kepler University, Austria), Dr. Marek Havlicek (Czech Metrology Institute, Czech Republic; Johannes Kepler University, Austria), Sandra Pluczyk and Prof. Mieczyslaw Lapkowski (Silesian University of Technology, Poland) as well as Prof. Eitan Ehrenfreund (Technion‐Israel Institute of Technology, Israel). The image illustrates the formation of bipolarons in P3HT at higher doping levels observed by in situ spectroscopic techniques. Read the full text of the article at 10.1002/cphc.201600961.

The major challenge in organic electronics concerns the stability of organic semiconductor materials which affects the operational lifetime of devices. Recent reports have shown that hydrogen‐bonded pigments of the indigoid family are air‐ and moisture resistant. The magenta pigment quinacridone, a hydrogen‐bonded molecule in the solid state with a pentacene like frame, is a perfect example for extraordinary chemical stability. Here, studies using in situ spectroscopic methods comparing quinacridone and pentacene are presented. A different spectral response of their radical cations is observed upon chemical doping. While in pentacene the barrier between doping and irreversible overoxidation is small, this stability toward overoxidation is increased by the heteroatomic structure, leading to hydrogen‐bonded quinacridone. This work provides insight into molecular design principles that may lead to next‐generation organic semiconductors with enhanced stability and performance.

The molecular-scale changes of the pigment quinacridone, a hydrogen-bonded organic semiconductor, are evaluated during redox reactions.