@article{VermaSteinbacherSchmiedeletal.2016, author = {Verma, Pramod Kumar and Steinbacher, Andreas and Schmiedel, Alexander and Nuernberger, Patrick and Brixner, Tobias}, title = {Excited-state intramolecular proton transfer of 2-acetylindan-1,3-dione studied by ultrafast absorption and fluorescence spectroscopy}, series = {Structural Dynamics}, volume = {3}, journal = {Structural Dynamics}, doi = {10.1063/1.4937363}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181301}, year = {2016}, abstract = {We employ transient absorption from the deep-UV to the visible region and fluorescence upconversion to investigate the photoinduced excited-state intramolecular proton-transfer dynamics in a biologically relevant drug molecule, 2-acetylindan-1,3-dione. The molecule is a ß-diketone which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond. Upon electronic excitation at 300 nm, the first excited state of the exocyclic enol is initially populated, followed by ultrafast proton transfer (≈160 fs) to form the vibrationally hot endocyclic enol. Subsequently, solvent-induced vibrational relaxation takes place (≈10 ps) followed by decay (≈390 ps) to the corresponding ground state.}, language = {en} } @unpublished{LambertVoelkerKochetal.2015, author = {Lambert, Christoph and V{\"o}lker, Sebastian F. and Koch, Federico and Schmiedel, Alexander and Holzapfel, Marco and Humeniuk, Alexander and R{\"o}hr, Merle I. S. and Mitric, Roland and Brixner, Tobias}, title = {Energy Transfer Between Squaraine Polymer Sections: From helix to zig-zag and All the Way Back}, series = {Journal of the American Chemical Society}, journal = {Journal of the American Chemical Society}, doi = {10.1021/jacs.5b03644}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159607}, year = {2015}, abstract = {Joint experimental and theoretical study of the absorption spectra of squaraine polymers in solution provide evidence that two different conformations are present in solution: a helix and a zig-zag structure. This unique situation allows investigating ultrafast energy transfer processes between different structural segments within a single polymer chain in solution. The understanding of the underlying dynamics is of fundamental importance for the development of novel materials for light-harvesting and optoelectronic applications. We combine here femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy showing that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zig-zag segments or vice versa, depending on the solvent as well as on the excitation wavenumber. These observations contrast other conjugated polymers such as MEH-PPV where much slower intrachain energy transfer was reported. The reason for the very fast energy transfer in squaraine polymers is most likely a close matching of the density of states between donor and acceptor polymer segments because of very small reorganization energy in these cyanine-like chromophores.}, language = {en} } @unpublished{HuberPresWittmannetal.2019, author = {Huber, Bernhard and Pres, Sebastian and Wittmann, Emanuel and Dietrich, Lysanne and L{\"u}ttig, Julian and Fersch, Daniel and Krauss, Enno and Friedrich, Daniel and Kern, Johannes and Lisinetskii, Victor and Hensen, Matthias and Hecht, Bert and Bratschitsch, Rudolf and Riedle, Eberhard and Brixner, Tobias}, title = {Space- and time-resolved UV-to-NIR surface spectroscopy and 2D nanoscopy at 1 MHz repetition rate}, issn = {0034-6748}, doi = {10.1063/1.5115322}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-191906}, year = {2019}, abstract = {We describe a setup for time-resolved photoemission electron microscopy (TRPEEM) with aberration correction enabling 3 nm spatial resolution and sub-20 fs temporal resolution. The latter is realized by our development of a widely tunable (215-970 nm) noncollinear optical parametric amplifier (NOPA) at 1 MHz repetition rate. We discuss several exemplary applications. Efficient photoemission from plasmonic Au nanoresonators is investigated with phase-coherent pulse pairs from an actively stabilized interferometer. More complex excitation fields are created with a liquid-crystal-based pulse shaper enabling amplitude and phase shaping of NOPA pulses with spectral components from 600 to 800 nm. With this system we demonstrate spectroscopy within a single plasmonic nanoslit resonator by spectral amplitude shaping and investigate the local field dynamics with coherent two-dimensional (2D) spectroscopy at the nanometer length scale ("2D nanoscopy"). We show that the local response varies across a distance as small as 33 nm in our sample. Further, we report two-color pump-probe experiments using two independent NOPA beamlines. We extract local variations of the excited-state dynamics of a monolayered 2D material (WSe2) that we correlate with low-energy electron microscopy (LEEM) and reflectivity (LEER) measurements. Finally, we demonstrate the in-situ sample preparation capabilities for organic thin films and their characterization via spatially resolved electron diffraction and dark-field LEEM.}, language = {en} } @article{SuessWehnerDostaletal.2019, author = {S{\"u}ß, Jasmin and Wehner, Johannes G. and Dost{\´a}l, Jakub and Engel, Volker and Brixner, Tobias}, title = {Mapping of exciton-exciton annihilation in a molecular dimer via fifth-order femtosecond two-dimensional spectroscopy}, series = {Journal of Physical Chemistry Letters}, volume = {150}, journal = {Journal of Physical Chemistry Letters}, number = {10}, doi = {10.1063/1.5086151}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178420}, pages = {104304}, year = {2019}, abstract = {We present a theoretical study on exciton-exciton annihilation (EEA) in a molecular dimer. This process is monitored using a fifth-order coherent two-dimensional (2D) spectroscopy as was recently proposed by Dost{\´a}l et al. [Nat. Commun. 9, 2466 (2018)]. Using an electronic three-level system for each monomer, we analyze the different paths which contribute to the 2D spectrum. The spectrum is determined by two entangled relaxation processes, namely, the EEA and the direct relaxation of higher lying excited states. It is shown that the change of the spectrum as a function of a pulse delay can be linked directly to the presence of the EEA process.}, subject = {Exziton}, language = {en} } @unpublished{SuessWehnerDostaletal.2019, author = {S{\"u}ß, Jasmin and Wehner, Johannes G. and Dost{\´a}l, Jakub and Engel, Volker and Brixner, Tobias}, title = {Mapping of exciton-exciton annihilation in a molecular dimer via fifth-order femtosecond two-dimensional spectroscopy}, series = {Journal of Physical Chemistry Letters}, journal = {Journal of Physical Chemistry Letters}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178482}, year = {2019}, abstract = {We present a theoretical study on exciton-exciton annihilation (EEA) in a molecular dimer. This process is monitored using a fifth-order coherent two-dimensional (2D) spectroscopy as was recently proposed by Dost{\´a}l et al. [Nat. Commun. 9, 2466 (2018)]. Using an electronic three-level system for each monomer, we analyze the different paths which contribute to the 2D spectrum. The spectrum is determined by two entangled relaxation processes, namely, the EEA and the direct relaxation of higher lying excited states. It is shown that the change of the spectrum as a function of a pulse delay can be linked directly to the presence of the EEA process.}, subject = {Exziton}, language = {en} } @unpublished{MuellerDraegerMaetal.2018, author = {M{\"u}ller, Stefan and Draeger, Simon and Ma, Kiaonan and Hensen, Matthias and Kenneweg, Tristan and Pfeiffer, Walter and Brixner, Tobias}, title = {Fluorescence-Detected Two-Quantum and One-Quantum-Two-Quantum 2D Electronic Spectroscopy}, series = {Journal of Physical Chemistry Letters}, journal = {Journal of Physical Chemistry Letters}, doi = {10.1021/acs.jpclett.8b00541}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173468}, year = {2018}, abstract = {We demonstrate two-quantum (2Q) coherent two-dimensional (2D)electronic spectroscopy using a shot-to-shot-modulated pulse shaper and fluorescence detection. Broadband collinear excitation is realized with the supercontinuum output of an argon-filled hollow-core fiber, enabling us to excite multiple transitions simultaneously in the visible range. The 2Q contribution is extracted via a three-pulse sequence with 16-fold phase cycling and simulated employing cresyl violet as a model system. Furthermore, we report the first experimental realization of one-quantum-two-quantum (1Q-2Q) 2D spectroscopy, offering less congested spectra as compared with the 2Q implementation. We avoid scattering artifacts and nonresonant solvent contributions by using fluorescence as the observable. This allows us to extract quantitative information about doubly excited states that agree with literature expectations. The high sensitivity and background-free nature of fluorescence detection allow for a general applicability of this method to many other systems.}, subject = {Fluoreszenz}, language = {en} } @article{HocheSchulzDietrichetal.2019, author = {Hoche, Joscha and Schulz, Alexander and Dietrich, Lysanne Monika and Humeniuk, Alexander and Stolte, Matthias and Schmidt, David and Brixner, Tobias and W{\"u}rthner, Frank and Mitric, Roland}, title = {The origin of the solvent dependence of fluorescence quantum yields in dipolar merocyanine dyes}, series = {Chemical Science}, volume = {10}, journal = {Chemical Science}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198707}, pages = {11013}, year = {2019}, abstract = {Fluorophores with high quantum yields are desired for a variety of applications. Optimization of promising chromophores requires an understanding of the non-radiative decay channels that compete with the emission of photons. We synthesized a new derivative of the famous laser dye 4-dicyanomethylen-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM),i.e., merocyanine 4-(dicyanomethylene)-2-tert-butyl-6-[3-(3-butyl-benzothiazol-2-ylidene)1-propenyl]-4H-pyran (DCBT). We measured fluorescence lifetimes and quantum yields in a variety of solvents and found a trend opposite to the energy gap law.This motivated a theoretical investigation into the possible non-radiative decay channels. We propose that a barrier to a conical intersection exists that is very sensitive to the solvent polarity. The conical intersection is characterized by a twisted geometry which allows a subsequent photoisomerization. Transient absorption measurements confirmed the formation of a photoisomer in unpolar solvents, while the measurements of fluorescence quantum yields at low temperature demonstrated the existence of an activation energy barrier.}, language = {en} } @article{KanalKeiberEcketal.2014, author = {Kanal, Florian and Keiber, Sabine and Eck, Reiner and Brixner, Tobias}, title = {100-kHz shot-to-shot broadband data acquisition for high-repetition-rate pump-probe spectroscopy}, doi = {10.1364/OE.22.016965}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-112853}, year = {2014}, abstract = {Shot-to-shot broadband detection is common in ultrafast pump-probe spectroscopy. Taking advantage of the intensity correlation of subsequent laser pulses improves the signal-to-noise ratio. Finite data readout times of CCD chips in the employed spectrometer and the maximum available speed of mechanical pump-beam choppers typically limit this approach to lasers with repetition rates of a few kHz. For high-repetition (≥ 100 kHz) systems, one typically averages over a larger number of laser shots leading to inferior signal-to-noise ratios or longer measurement times. Here we demonstrate broadband shot-to-shot detection in transient absorption spectroscopy with a 100-kHz femtosecond laser system. This is made possible using a home-built high-speed chopper with external laser synchronization and a fast CCD line camera. Shot-to-shot detection can reduce the data acquisition time by two orders of magnitude compared to few-kHz lasers while keeping the same signal-to-noise ratio.}, language = {en} } @article{BrixnerPawłowskaGoetzetal.2014, author = {Brixner, Tobias and Pawłowska, Monika and Goetz, Sebastian and Dreher, Christian and Wurdack, Matthias and Krauss, Enno and Razinskas, Gary and Geisler, Peter and Hecht, Bert}, title = {Shaping and spatiotemporal characterization of sub-10-fs pulses focused by a high-NA objective}, doi = {10.1364/OE.22.031496}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-111120}, year = {2014}, abstract = {We describe a setup consisting of a 4 f pulse shaper and a microscope with a high-NA objective lens and discuss the spects most relevant for an undistorted spatiotemporal profile of the focused beam. We demonstrate shaper-assisted pulse compression in focus to a sub-10-fs duration using phase-resolved interferometric spectral modulation (PRISM). We introduce a nanostructure-based method for sub-diffraction spatiotemporal characterization of strongly focused pulses. The distortions caused by optical aberrations and space-time coupling from the shaper can be reduced by careful setup design and alignment to about 10 nm in space and 1 fs in time.}, language = {en} } @article{RewitzKeitzlTuchschereretal.2012, author = {Rewitz, Christian and Keitzl, Thomas and Tuchscherer, Philip and Goetz, Sebastian and Geisler, Peter and Razinskas, Gary and Hecht, Bert and Brixner, Tobias}, title = {Spectral-interference microscopy for characterization of functional plasmonic elements}, series = {Optics Express}, journal = {Optics Express}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-85922}, year = {2012}, abstract = {Plasmonic modes supported by noble-metal nanostructures offer strong subwavelength electric-field confinement and promise the realization of nanometer-scale integrated optical circuits with well-defined functionality. In order to measure the spectral and spatial response functions of such plasmonic elements, we combine a confocal microscope setup with spectral interferometry detection. The setup, data acquisition, and data evaluation are discussed in detail by means of exemplary experiments involving propagating plasmons transmitted through silver nanowires. By considering and experimentally calibrating any setup-inherent signal delay with an accuracy of 1 fs, we are able to extract correct timing information of propagating plasmons. The method can be applied, e.g., to determine the dispersion and group velocity of propagating plasmons in nanostructures, and can be extended towards the investigation of nonlinear phenomena.}, language = {en} }