Während die deutschen Medien im April 2016 die Veröffentlichung der Panama Papers, den Krieg in Syrien und die bevorstehenden Olympischen Spiele in Rio verfolgten, ereignete sich, von der Weltöffentlichkeit scheinbar unbemerkt, die schlimmste ökologische Katastrophe in der Geschichte des Landes. Eindeutigstes Indiz: Ein Meer toter Fische und eine Bevölkerung in Aufruhr.(Elektronische Langversion des im Druck erschienenen Artikels.)
Conjugated polymers conduct both electronic and ionic carriers and thus can stimulate and translate biological signals when used as active materials in bioelectronic devices. Self- and on-demand organization of the active material directly in the in vivo environment can result in the seamless integration of the bioelectronic interface. Along that line, we recently demonstrated spontaneous in vivo polymerization of the conjugated oligomer ETE-S in the vascular tissue of plants and the formation of conducting wires. In this work, we elucidate the mechanism of the in vivo polymerization of the ETE-S trimer and demonstrate that ETE-S polymerizes due to an enzymatic reaction where the enzyme peroxidase is the catalyst and hydrogen peroxide is the oxidant. ETE-S, therefore, represents the first example of a conducting polymer that is enzymatically polymerized in vivo. By reproducing the reaction in vitro, we gain further insight on the polymerization mechanism and show that hydrogen peroxide is the limiting factor. In plants the ETE-S triggers the catalytic cycle responsible for the lignification process, hacks this biochemical pathway and integrates within the plant cell wall, forming conductors along the plant structure. ; Funding Agencies|European UnionEuropean Union (EU) [800926]; Swedish Research Council (VR)Swedish Research Council; Wallenberg Wood Science Center [KAW 2018.0452]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research; European Research Council (ERC) project e-NeuroPharmaEuropean Research Council (ERC) [834677]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; LOreal-Unesco For Women in Science (FWIS); Department of EnergyUnited States Department of Energy (DOE) [DE-SC0017659]
Despite significant efforts, a complete mechanistic understanding of thermally activated delayed fluorescence (TADF) materials has not yet been fully uncovered. Part of the complexity arises from the apparent dichotomy between the need for close energy resonance and for a significant spin-orbit coupling between alike charge-transfer singlet and triplet excitations. Here we show, in the case of reference carbazole derivatives, that this dichotomy can be resolved in a fully atomistic model accounting for thermal fluctuations of the molecular conformations and microscopic electronic polarization effects in amorphous films. These effects yield electronic excitations with a dynamically mixed charge-transfer and localized character, resulting in thermally averaged singlet-triplet energy differences and interconversion rates in excellent agreement with careful spectroscopic studies. ; The work in Mons was supported by the Programme d'Excellence de la Région Wallonne (OPTI2MAT project), the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 646176 (EXTMOS project), and FNRS-FRFC. Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11, as well as the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by theWalloon Region under Grant Agreement No. 1117545. B.Y. and T.Q.N. thank the Department of the Navy, Office of Naval Research (Award No. N00014-14-1-0580) for support. L.M. acknowledges funding by the French national grant ANR-10-LABX-0042-AMADEus managed by the National Research Agency under the initiative of excellence IdEx Bordeaux program (reference ANR-10-IDEX-0003-02). G.D. acknowledges support from EU through the FP7-PEOPLE-2013-IEF program (Project No. 625198).
While it has been argued that field-dependent geminate pair recombination (GR) is important, this process is often disregarded when analyzing the recombination kinetics in bulk heterojunction organic solar cells (OSCs). To differentiate between the contributions of GR and nongeminate recombination (NGR) the authors study bilayer OSCs using either a PCDTBTtype polymer layer with a thickness from 14 to 66 nm or a 60 nm thick p-DTS(FBTTh2)(2) layer as donor material and C-60 as acceptor. The authors measure JV-characteristics as a function of intensity and charge-extraction-by-linearly-increasing-voltage-type hole mobilities. The experiments have been complemented by Monte Carlo simulations. The authors find that fill factor (FF) decreases with increasing donor layer thickness (L-p) even at the lowest light intensities where geminate recombination dominates. The authors interpret this in terms of thickness dependent back diffusion of holes toward their siblings at the donor-acceptor interface that are already beyond the Langevin capture sphere rather than to charge accumulation at the donor-acceptor interface. This effect is absent in the p-DTS(FBTTh2)(2) diode in which the hole mobility is by two orders of magnitude higher. At higher light intensities, NGR occurs as evidenced by the evolution of s-shape of the JV-curves and the concomitant additional decrease of the FF with increasing layer thickness. ; The authors acknowledge financial support by the Bavarian State Ministry of Science, Research, and the Arts through the Collaborative Research Network "Solar Technologies go Hybrid", by the Volkswagen foundation and by the German Science Foundation DFG through the doctoral training center "GRK 1640." This project further received funding from the Universidad Carlos III de Madrid, the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no. 600371, el Ministerio de Economía y Competitividad (COFUND2014-51509), el Ministerio de Educación, cultura y Deporte (CEI-15-17), and Banco Santander. M.R. additionally acknowledges support from the Hanns Seidel Foundation for a stipend through funds from the German Ministry of Education and Research (BMBF). T.-Q.N. thanks the Office of Naval Research (#N000141410076) for the support. Furthermore, the authors would like to thank the anonymous referees for helpful suggestions.
