TY - JOUR A1 - Weissenseel, Sebastian A1 - Gottscholl, Andreas A1 - Bönnighausen, Rebecca A1 - Dyakonov, Vladimir A1 - Sperlich, Andreas T1 - Long-lived spin-polarized intermolecular exciplex states in thermally activated delayed fluorescence-based organic light-emitting diodes JF - Science Advances N2 - Spin-spin interactions in organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) are pivotal because radiative recombination is largely determined by triplet-to-singlet conversion, also called reverse intersystem crossing (RISC). To explore the underlying process, we apply a spin-resonance spectral hole-burning technique to probe electroluminescence. We find that the triplet exciplex states in OLEDs are highly spin-polarized and show that these states can be decoupled from the heterogeneous nuclear environment as a source of spin dephasing and can even be coherently manipulated on a spin-spin relaxation time scale T-2* of 30 ns. Crucially, we obtain the characteristic triplet exciplex spin-lattice relaxation time T-1 in the range of 50 mu s, which far exceeds the RISC time. We conclude that slow spin relaxation rather than RISC is an efficiency-limiting step for intermolecular donor:acceptor systems. Finding TADF emitters with faster spin relaxation will benefit this type of TADF OLEDs. KW - detected magnetic-resonance KW - population oscillations KW - polaron delocalization KW - charge separation KW - hole KW - phosphorescence KW - singlet KW - absorption KW - tryptophan KW - emission Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-265508 VL - 7 IS - 47 ER - TY - JOUR A1 - Shukla, A. A1 - Mannheim, K. T1 - Gamma-ray flares from relativistic magnetic reconnection in the jet of the quasar 3C 279 JF - Nature Communications N2 - Spinning black holes in the centres of galaxies can release powerful magnetised jets. When the jets are observed at angles of less than a few degrees to the line-of-sight, they are called blazars, showing variable non-thermal emission across the electromagnetic spectrum from radio waves to gamma rays. It is commonly believed that shock waves are responsible for this dissipation of jet energy. Here we show that gamma-ray observations of the blazar 3C 279 with the space-borne telescope Fermi-LAT reveal a characteristic peak-in-peak variability pattern on time scales of minutes expected if the particle acceleration is instead due to relativistic magnetic reconnection. The absence of gamma-ray pair attenuation shows that particle acceleration takes place at a distance of ten thousand gravitational radii from the black hole where the fluid dynamical kink instability drives plasma turbulence. KW - kink instability KW - energy KW - radiation KW - blazars KW - variability KW - absorption KW - telescope KW - shocks Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-231328 VL - 11 ER - TY - JOUR A1 - Lohse, Christian A1 - Bock, Andreas A1 - Maiellaro, Isabella A1 - Hannawacker, Annette A1 - Schad, Lothar R. A1 - Lohse, Martin J. A1 - Bauer, Wolfgang R. T1 - Experimental and mathematical analysis of cAMP nanodomains JF - PLoS ONE N2 - In their role as second messengers, cyclic nucleotides such as cAMP have a variety of intracellular effects. These complex tasks demand a highly organized orchestration of spatially and temporally confined cAMP action which should be best achieved by compartmentalization of the latter. A great body of evidence suggests that cAMP compartments may be established and maintained by cAMP degrading enzymes, e.g. phosphodiesterases (PDEs). However, the molecular and biophysical details of how PDEs can orchestrate cAMP gradients are entirely unclear. In this paper, using fusion proteins of cAMP FRET-sensors and PDEs in living cells, we provide direct experimental evidence that the cAMP concentration in the vicinity of an individual PDE molecule is below the detection limit of our FRET sensors (<100nM). This cAMP gradient persists in crude cytosol preparations. We developed mathematical models based on diffusion-reaction equations which describe the creation of nanocompartments around a single PDE molecule and more complex spatial PDE arrangements. The analytically solvable equations derived here explicitly determine how the capability of a single PDE, or PDE complexes, to create a nanocompartment depend on the cAMP degradation rate, the diffusive mobility of cAMP, and geometrical and topological parameters. We apply these generic models to our experimental data and determine the diffusive mobility and degradation rate of cAMP. The results obtained for these parameters differ by far from data in literature for free soluble cAMP interacting with PDE. Hence, restricted cAMP diffusion in the vincinity of PDE is necessary to create cAMP nanocompartments in cells. KW - fluorescence resonance energy transfer KW - yellow fluorescent protein KW - radii KW - adenylyl cyclase signaling cascade KW - cell fusion KW - cytosol KW - isoproterenol KW - absorption KW - cyclic nucleotides such as cyclic adenosine monophosphate Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170972 VL - 12 IS - 4 ER - TY - JOUR A1 - Sauer, C A1 - Wießner, M A1 - Schöll, A A1 - Reinert, F T1 - Observation of a molecule-metal interface charge transfer related feature by resonant photoelectron spectroscopy JF - New Journal of Physics N2 - We report the discovery of a charge transfer (CT) related low binding energy feature at a molecule-metal interface by the application of resonant photoelectron spectroscopy (RPES). This interface feature is neither present for molecular bulk samples nor for the clean substrate. A detailed analysis of the spectroscopic signature of the low binding energy feature shows characteristics of electronic interaction not found in other electron spectroscopic techniques. Within a cluster model description this feature is assigned to a particular eigenstate of the photoionized system that is invisible in direct photoelectron spectroscopy but revealed in RPES through a relative resonant enhancement. Interpretations based on considering only the predominant character of the eigenstates explain the low binding energy feature by an occupied lowest unoccupied molecular orbital, which is either realized through CT in the ground or in the intermediate state. This reveals that molecule-metal CT is responsible for this feature. Consequently, our study demonstrates the sensitivity of RPES to electronic interactions and constitutes a new way to investigate CT at molecule-metal interfaces. KW - transfer dynamics KW - photoemission KW - states KW - interface KW - charge transfer KW - organic thin films KW - resonant photoelectron spectroscopy KW - energy KW - model calculation KW - NEXAFS spectroscopy KW - ce compounds KW - absorption Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148672 VL - 17 IS - 043016 ER - TY - JOUR A1 - Sung, Jooyoung A1 - Kim, Pyosang A1 - Fimmel, Benjamin A1 - Würthner, Frank A1 - Kim, Dongho T1 - Direct observation of ultrafast coherent exciton dynamics in helical π-stacks of self-assembled perylene bisimides JF - Nature Communications N2 - Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with pi-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π-π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process. KW - systems KW - molecules KW - J-aggregate behavior KW - absorption KW - spectroscopy KW - photoluminescence KW - diffusion KW - fluorescence KW - excimer formation KW - organic semiconductors Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148157 VL - 6 IS - 8646 ER -