@phdthesis{Issler2024, author = {Issler, Kevin}, title = {Theory and simulation of ultrafast autodetachment dynamics and nonradiative relaxation in molecules}, doi = {10.25972/OPUS-35223}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352232}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {In this thesis, theoretical approaches for the simulation of electron detachment processes in molecules following vibrational or electronic excitation are developed and applied. These approaches are based on the quantum-classical surface-hopping methodology, in which nuclear motion is treated classically as an ensemble of trajectories in the potential of quantum-mechanically described electronic degrees of freedom.}, subject = {Theoretische Chemie}, language = {en} } @phdthesis{Pres2024, author = {Pres, Sebastian}, title = {Detection of a plasmon-polariton quantum wave packet by coherent 2D nanoscopy}, doi = {10.25972/OPUS-34824}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-348242}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {Plasmonic nanostructures are considered promising candidates for essential components of integrated quantum technologies because of their ability to efficiently localize broad-band electromagnetic fields on the nanoscale. The resulting local near field can be understood as a spatial superposition of spectrally different plasmon-polariton modes due to the spectrally broad optical excitation, and thus can be described as a classical wave packet. Since plasmon polaritons, in turn, can transmit and receive non-classical light states, the exciting question arises to what extent they have to be described as quantum mechanical wave packets, i.e. as a superposition of different quantum states. But how to probe, characterize and eventually manipulate the quantum state of such plasmon polaritons? Up to now, probing at room temperatures relied completely on analyzing quantum optical properties of the corresponding in-going and out-going far-field photon modes. However, these methods so far only allow a rather indirect investigation of the plasmon-polariton quantum state by means of transfer into photons. Moreover, these indirect methods lack spatial resolution and therefore do not provide on-site access to the plasmon-polariton quantum state. However, since the spectroscopic method of coherent two-dimensional (2D) nanoscopy offers the capability to follow the plasmon- polariton quantum state both in Hilbert space and in space and time domain a complete characterization of the plasmon polariton is possible. In this thesis a versatile coherent 2D nanoscopy setup is presented combining spectral tunability and femtosecond time resolution with spatial resolution on the nanometer scale due to the detection of optically excited nonlinear emitted electrons via photoemission electron microscopy (PEEM). Optical excitation by amplitude- and phase-shaped, systematically-modified and interferometric-stable multipulse sequences is realized, and characterized via Fourier-transform spectral interferometry (FTSI). This linear technique enables efficient data acquisition in parallel to a simultaneously performed experiment. The full electric-field reconstruction of every generated multipulse sequence is used to analyze the effect of non-ideal pulse sequences on the two-dimensional spectral data of population-based multidimensional spectroscopy methods like, e.g., the coherent 2D nanoscopy applied in this thesis. Investigation of the spatially-resolved nonlinear electron emission yield from plasmonic gold nanoresonators by coherent 2D nanoscopy requires a quasi-particle treatment of the addressed plasmon-polariton mode and development of a quantum model to adequately describe the plasmon-assisted multi-quantum electron emission from nanostructures. Good agreement between simulated and experimental data enables to connect certain spectral features to superpositions of non-adjacent plasmon-polariton quantum states, i.e, non-adjacent occupation-number states of the underlying quantized, harmonic oscillator, thus direct probing of the plasmon-polariton quantum wave packet at the location of the nanostructure. This is a necessary step to locally control and manipulate the plasmon-polariton quantum state and thus of general interest for the realization of nanoscale quantum optical devices.}, subject = {Coherent Multidimensional Spectroscopy}, language = {en} } @phdthesis{Herok2024, author = {Herok, Christoph}, title = {Quantum Chemical Exploration of Potential Energy Surfaces: Reaction Cycles and Luminescence Phenomena}, doi = {10.25972/OPUS-35218}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352185}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {This work aims at elucidating chemical processes involving homogeneous catalysis and photo-physical relaxation of excited molecules in the solid state. Furthermore, compounds with supposedly small singlet-triplet gaps and therefore biradicaloid character are investigated with respect to their electro-chemical behavior. The work on hydroboration catalysis via a reduced 9,10-diboraanthracene (DBA) was preformed in collaboration with the Wagner group in Frankfurt, more specifically Dr. Sven Prey, who performed all laboratory experiments. The investigation of delayed luminescence properties in arylboronic esters in their solid state was conducted in collaboration with the Marder group in W{\"u}rzburg. The author of this work took part in the synthesis of the investigated compounds while being supervised by Dr. Zhu Wu. The final project was a collaboration with the group of Anukul Jana from Hyderabad, India who provided the experimental data.}, subject = {Simulation}, language = {en} } @phdthesis{Schuerger2024, author = {Sch{\"u}rger, Peter}, title = {Information-Theoretical Studies on Time-Dependent Quantum Systems}, doi = {10.25972/OPUS-35221}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352215}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {In this thesis, we apply the information-theoretic approach in the context of quantum dynamics and wave packet motion: Information-theoretic measures are calculated from position and momentum densities, which are obtained from time-dependent quantum wave functions. The aim of this thesis is to benchmark, analyze and interpret these quantities and relate their features to the wave packet dynamics. Firstly, this is done for the harmonic oscillator (HO) with and without static disorder. In the unperturbed HO, the analytical study of coherent and squeezed states reveals time-dependent entropy expressions related to the localization of the wave function. In the disordered HO, entropies from classical and quantum dynamics are compared for short and long times. In the quantum case, imprints of wave packet revivals are found in the entropy. Then, the energy dependence of the entropy for very long times is discussed. Secondly, this is donefor correlated electron-nuclear motion. Here, entropies derived from the total, electronic and nuclear density, respectively, are calculated in position and momentum space for weak and strong adiabatic electronic coupling. The correlation between electron and nucleus is investigated using different correlation measures, where some of these functions are sensitive to the nodal structure of the wave function. An analytic ansatz to interpret the information-theoretical quantities is applied as well.}, subject = {St{\"o}rungstheorie}, language = {en} } @phdthesis{Hoche2023, author = {Hoche, Joscha}, title = {The life of an exciton: From ultrafast nonradiative relaxation to high quantum yield fluorescence}, doi = {10.25972/OPUS-31684}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-316844}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {This thesis focuses on understanding and predicting processes in chromophores after electronic state excitation, particularly the impact on luminescence - the spontaneous emission of light. It considers the effect of processes preceding luminescence on emission properties, which are challenging to predict, especially in complex aggregates. For example, excitation energy transfer is a crucial process in understanding luminescence, as it allows the emission to occur from different molecular units than where the absorption occurs. This can lead to significant shifts in emission wavelength and fluorescence quantum yields. The thesis offers solutions to model this process effectively, understanding the impact of excitation energy and exciton coupling disorder on energy transfer rates and linking simulated energy transfer to experimental measurements. The work further explores excimer formation - an undesired luminescence loss channel due to its significant stabilization of the electronic state. Usually, the molecules obey a stacked conformation with parallel orientation to maximize the orbital overlap. This energetic lowering of the excited state can often result in trapping of the dimer in this state due to a deep minimum on the potential energy surface. The excimer formation dynamics, structural rearrangement, and its influence on singlet-correlated triplet pair states formation, critical for the singlet-fission process, have been extensively studied. The thesis also focuses on another luminescence loss channel triggered by conical intersections between the electronic ground and the first excited states. A new model is introduced to overcome limitations in current simulation methods, considering the solvent's electrostatic and frictional effects on the barriers. The model accurately describes merocyanine dyes' solvent-dependent photoluminescence quantum yields and characterizes all relaxation channels in different BODIPY oligomer series.}, subject = {Theoretische Chemie}, language = {en} } @article{WeiserCuiDewhurstetal.2023, author = {Weiser, Jonas and Cui, Jingjing and Dewhurst, Rian D. and Braunschweig, Holger and Engels, Bernd and Fantuzzi, Felipe}, title = {Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand}, series = {Journal of Computational Chemistry}, volume = {44}, journal = {Journal of Computational Chemistry}, number = {3}, doi = {10.1002/jcc.26994}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312586}, pages = {456 -- 467}, year = {2023}, abstract = {The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13-15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space π bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry.}, language = {en} } @article{PreitschopfSturmStroganovaetal.2023, author = {Preitschopf, Tobias and Sturm, Floriane and Stroganova, Iuliia and Lemmens, Alexander K. and Rijs, Anouk M. and Fischer, Ingo}, title = {IR/UV Double Resonance Study of the 2-Phenylallyl Radical and its Pyrolysis Products}, series = {Chemistry - A European Journal}, volume = {29}, journal = {Chemistry - A European Journal}, number = {13}, doi = {10.1002/chem.202202943}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312338}, year = {2023}, abstract = {Isolated 2-phenylallyl radicals (2-PA), generated by pyrolysis from a nitrite precursor, have been investigated by IR/UV ion dip spectroscopy using free electron laser radiation. 2-PA is a resonance-stabilized radical that is considered to be involved in the formation of polycyclic aromatic hydrocarbons (PAH) in combustion, but also in interstellar space. The radical is identified based on its gas-phase IR spectrum. Furthermore, a number of bimolecular reaction products are identified, showing that the self-reaction as well as reactions with unimolecular decomposition products of 2-PA form several PAH efficiently. Possible mechanisms are discussed and the chemistry of 2-PA is compared with the one of the related 2-methylallyl and phenylpropargyl radicals.}, language = {en} } @unpublished{FerschMalyRueheetal.2023, author = {Fersch, Daniel and Mal{\´y}, Pavel and R{\"u}he, Jessica and Lisinetskii, Victor and Hensen, Matthias and W{\"u}rthner, Frank and Brixner, Tobias}, title = {Single-Molecule Ultrafast Fluorescence-Detected Pump-Probe Microscopy}, doi = {10.25972/OPUS-31348}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-313485}, year = {2023}, abstract = {We introduce fluorescence-detected pump-probe microscopy by combining a wavelength-tunable ultrafast laser with a confocal scanning fluorescence microscope, enabling access to the femtosecond time scale on the micrometer spatial scale. In addition, we obtain spectral information from Fourier transformation over excitation pulse-pair time delays. We demonstrate this new approach on a model system of a terrylene bisimide (TBI) dye embedded in a PMMA matrix and acquire the linear excitation spectrum as well as time-dependent pump-probe spectra simultaneously. We then push the technique towards single TBI molecules and analyze the statistical distribution of their excitation spectra. Furthermore, we demonstrate the ultrafast transient evolution of several individual molecules, highlighting their different behavior in contrast to the ensemble due to their individual local environment. By correlating the linear and nonlinear spectra, we assess the effect of the molecular environment on the excited-state energy.}, subject = {Fluoreszenz}, language = {en} } @unpublished{DietzschJayachandranMuelleretal.2023, author = {Dietzsch, Julia and Jayachandran, Ajay and Mueller, Stefan and H{\"o}bartner, Claudia and Brixner, Tobias}, title = {Excitonic coupling of RNA-templated merocyanine dimer studied by higher-order transient absorption spectroscopy}, series = {Chemical Communications}, journal = {Chemical Communications}, edition = {submitted version}, doi = {10.1039/D3CC02024J}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327772}, year = {2023}, abstract = {We report the synthesis and spectroscopic analysis of RNA containing the barbituric acid merocyanine rBAM2 as a nucleobase surrogate. Incorporation into RNA strands by solid-phase synthesis leads to fluorescence enhancement compared to the free chromophore. In addition, linear absorption studies show the formation of an excitonically coupled H-type dimer in the hybridized duplex. Ultrafast third- and fifth-order transient absorption spectroscopy of this non-fluorescent dimer suggests immediate (sub-200 fs) exciton transfer and annihilation due to the proximity of the rBAM2 units.}, language = {en} } @phdthesis{Matthaei2023, author = {Matthaei, Christian Tobias}, title = {Studying the Photodissociation of Chlorine-Containing Molecules with Velocity Map Imaging}, doi = {10.25972/OPUS-32740}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327405}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {The first is via direct dissociation and the second likely involves a barrier slowing down dissociation. Chlorine-containing hydrocarbons pose a great risk for the environment and especially for the atmosphere. In this thesis I present the photodissociation dynamics of multiple chlorine-containing molecules. The method of velocity map imaging was utilized for gaining information on the kinetic energy distribution of the fragments generated in the photodissociation reactions. First, the photodissociation of benzoyl chloride after excitation to the S1, S2 and the S3 state between 279 nm and 237 nm was studied. This stable molecule was an ideal candidate for demonstrating a new ionization scheme for chlorine atoms. It was shown that benzoyl chloride dissociates statistically from the ground state. Afterwards, the results from experiments on the radicals trichloromethyl and dichlorocarbene are presented in the range of 230 to 250 nm. These radicals remain after the dissociation of carbon tetrachloride and have not been studied in detail because of their instability. Trichlormethyl dissociates via two paths: The loss of a chlorine atom to dichlorocarbene and by decaying to CCl and a chlorine molecule. The dissociation to dichlorocarbene involves a barrier. If the photon exciting the molecule has enough energy to surpass the barrier, which is the case starting at around 235 nm, trichlormethyl dissociates rapidly resulting in an anisotropic VMI. However, if the the excitation energy is lower, the dissociation takes longer than a rotational period and the anisotropy is lost.The path to CCl is a statistical dissociation. Dichlorocarbene dissociates to CCl and Cl via to separate channels. The first is via direct dissociation and the second likely involves a barrier slowing down dissociation.}, subject = {Photodissoziation}, language = {en} }