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.
Alkoxyamines are heat-labile molecules, widely used as in-situ source of nitroxides in polymer and materials sciences. Here we show that the one-electron oxidation of an alkoxyamine leads to a cation radical intermediate that even at room temperature rapidly fragments releasing a nitroxide and carbocation. Digital simulations of experimental voltammetry and current-time transients suggest the unimolecular decomposition which yields the "unmasked" nitroxide (TEMPO) is exceedingly rapid and irreversible. High-level quantum computations indicate the collapse of the alkoxyamine cation radical is likely to yield a neutral nitroxide radical and a secondary phenylethyl cation. However, this fragmentation is predicted to be slow and energetically very unfavorable. To attain qualitative agreement between the experimental kinetics and computational modelling for this fragmentation step the explicit electrostatic environment within the double layer must be accounted for. Single-molecule break-junction experiments in a scanning tunneling microscope using solvent of low dielectric (STM-BJ technique) corroborate the role played by electrostatics forces on the lysis of the alkoxyamine CON bond. This work highlights the electrostatic aspects played by charged species in a chemical step that follows an electrochemical reaction, defines the magnitude of this catalytic effect by looking at an independent electrical technique in non-electrolyte systems (STM-BJ), and suggests a redox on/off switch to guide the cleavage of alkoxyamines at an electrified interface.
(2016) 'Exciplex enhancement as a tool to increase OLED device e ciency.', Journal of physical chemistry C., 120 (4). pp. 2070-2078. Further information on publisher's website:https://doi.org/10.1021/acs.jpcc.5b11263 Publisher's copyright statement: This document is the Accepted Manuscript version of a Published Work that appeared in nal form in Journal of physical chemistry C, copyright c American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see https://doi.org/10.1021/acs.jpcc.5b11263Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. derivatives that could be used as emitters in OLED devices. We were able to improve the of efficiency DPP materials by forming exciplex enhanced OLED devices. These organic materials were also characterized by electrochemical and spectroscopic methods in order to elucidate each molecule's interaction and decreasing the photoluminescence efficiency.2
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 ambipolar behavior of groups of N-substituted and core-functionalized triarylamine arylene bisimides were investigated by electrochemical and spectroelectrochemical (UV-vis and EPR spectroelectrochemistry) techniques.
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