@article{KuntzeViljakkaTitovetal.2022,
author = {Kuntze, Kim and Viljakka, Jani and Titov, Evgenii and Ahmed, Zafar and Kalenius, Elina and Saalfrank, Peter and Priimagi, Arri},
title = {Towards low-energy-light-driven bistable photoswitches},
series = {Photochemical \& photobiological sciences / European Society for Photobiology},
volume = {21},
journal = {Photochemical \& photobiological sciences / European Society for Photobiology},
number = {2},
publisher = {Springer},
address = {Heidelberg},
issn = {1474-905X},
doi = {10.1007/s43630-021-00145-4},
pages = {159 -- 173},
year = {2022},
abstract = {Thermally stable photoswitches that are driven with low-energy light are rare, yet crucial for extending the applicability of photoresponsive molecules and materials towards, e.g., living systems. Combined ortho-fluorination and -amination couples high visible light absorptivity of o-aminoazobenzenes with the extraordinary bistability of o-fluoroazobenzenes. Herein, we report a library of easily accessible o-aminofluoroazobenzenes and establish structure-property relationships regarding spectral qualities, visible light isomerization efficiency and thermal stability of the cis-isomer with respect to the degree of o-substitution and choice of amino substituent. We rationalize the experimental results with quantum chemical calculations, revealing the nature of low-lying excited states and providing insight into thermal isomerization. The synthesized azobenzenes absorb at up to 600 nm and their thermal cis-lifetimes range from milliseconds to months. The most unique example can be driven from trans to cis with any wavelength from UV up to 595 nm, while still exhibiting a thermal cis-lifetime of 81 days.
[GRAPHICS]
.},
language = {en}
}
@article{YueMelaniKirschetal.2022,
author = {Yue, Yanhua and Melani, Giacomo and Kirsch, Harald and Paarmann, Alexander and Saalfrank, Peter and Campen, Richard Kramer and Tong, Yujin},
title = {Structure and Reactivity of a-Al2O3(0001) Surfaces: How Do Al-I and Gibbsite-like Terminations Interconvert?},
series = {The journal of physical chemistry / publ. weekly by the American Chemical Society. C, Energy, materials, and catalysis},
volume = {126},
journal = {The journal of physical chemistry / publ. weekly by the American Chemical Society. C, Energy, materials, and catalysis},
number = {31},
publisher = {American Chemical Society},
address = {Washington},
issn = {1932-7447},
doi = {10.1021/acs.jpcc.2c03743},
pages = {13467 -- 13476},
year = {2022},
abstract = {The alpha-Al2O3(0001) surface has been extensively studied because of its significance in both fundamental research and application. Prior work suggests that in ultra-high-vacuum (UHV), in the absence of water, the so-called Al-I termination is thermodynamically favored, while in ambient, in contact with liquid water, a Gibbsite-like layer is created. While the view of the alpha- Al2O3(0001)/H2O(l) interface appears relatively clear in theory, experimental characterization of this system has resulted in estimates of surface acidity, i.e., isoelectric points, that differ by 4 pH units and surface structure that in some reports has non-hydrogen-bonded surface aluminol (Al-OH) groups and in others does not. In this study, we employed vibrational sum frequency spectroscopy (VSFS) and density functional theory (DFT) simulation to study the surface phonon modes of the differently terminated alpha-Al2O3(0001) surfaces in both UHV and ambient. We find that, on either water dosing of the Al-I in UHV or heat-induced dehydroxylation of the Gibbsite-like in ambient, the surfaces do not interconvert. This observation offers a new explanation for disagreements in prior work on the alpha-Al2O3(0001)/liquid water interface -different preparation methods may create surfaces that do not interconvert-and shows that the surface phonon spectral response offers a novel probe of interfacial hydrogen bonding structure.},
language = {en}
}
@article{MullanMaschioSaalfranketal.2022,
author = {Mullan, Thomas and Maschio, Lorenzo and Saalfrank, Peter and Usvyat, Denis},
title = {Reaction barriers on non-conducting surfaces beyond periodic local MP2},
series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
volume = {156},
journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
number = {7},
publisher = {AIP Publishing},
address = {Melville},
issn = {0021-9606},
doi = {10.1063/5.0082805},
pages = {11},
year = {2022},
abstract = {The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a alpha-Al2O3 (0001) surface, aiming for a couple cluster singles, doubles, and perturbative triples [CCSD(T)]-level benchmark. We employ the density functional theory (DFT) optimized minimum and transition state structures reported by Heiden, Usvyat, and Saalfrank [J. Phys. Chem. C 123, 6675 (2019)]. The barrier is first evaluated at the periodic Hartree-Fock and local Moller-Plesset second-order perturbation (MP2) level of theory. The possible sources of errors are then analyzed, which includes basis set incompleteness error, frozen core, density fitting, local approximation errors, as well as the MP2 method error. Using periodic and embedded fragment models, corrections to these errors are evaluated. In particular, two corrections are found to be non-negligible (both from the chemical accuracy perspective and at the scale of the barrier value of 0.72 eV): the correction to the frozen core-approximation of 0.06 eV and the CCSD(T) correction of 0.07 eV. Our correlated wave function results are compared to barriers obtained from DFT. Among the tested DFT functionals, the best performing for this barrier is B3LYP-D3.},
language = {en}
}
@article{YangGhoshRoeseretal.2022,
author = {Yang, Jin and Ghosh, Samrat and Roeser, J{\´e}r{\^o}me and Acharjya, Amitava and Penschke, Christopher and Tsutsui, Yusuke and Rabeah, Jabor and Wang, Tianyi and Tameu, Simon Yves Djoko and Ye, Meng-Yang and Gr{\"u}neberg, Julia and Li, Shuang and Li, Changxia and Schomaecker, Reinhard and Van de Krol, Roel and Seki, Shu and Saalfrank, Peter and Thomas, Arne},
title = {Constitutional isomerism of the linkages in donor-acceptor covalent organic frameworks and its impact on photocatalysis},
series = {Nature Communications},
volume = {13},
journal = {Nature Communications},
number = {1},
publisher = {Nature Publishing Group UK},
address = {[London]},
issn = {2041-1723},
doi = {10.1038/s41467-022-33875-9},
pages = {10},
year = {2022},
abstract = {When new covalent organic frameworks (COFs) are designed, the main efforts are typically focused on selecting specific building blocks with certain geometries and properties to control the structure and function of the final COFs. The nature of the linkage (imine, boroxine, vinyl, etc.) between these building blocks naturally also defines their properties. However, besides the linkage type, the orientation, i.e., the constitutional isomerism of these linkages, has rarely been considered so far as an essential aspect. In this work, three pairs of constitutionally isomeric imine-linked donor-acceptor (D-A) COFs are synthesized, which are different in the orientation of the imine bonds (D-C=N-A (DCNA) and D-N=C-A (DNCA)). The constitutional isomers show substantial differences in their photophysical properties and consequently in their photocatalytic performance. Indeed, all DCNA COFs show enhanced photocatalytic H2 evolution performance than the corresponding DNCA COFs. Besides the imine COFs shown here, it can be concluded that the proposed concept of constitutional isomerism of linkages in COFs is quite universal and should be considered when designing and tuning the properties of COFs.},
language = {en}
}
@article{BouaklineSaalfrank2021,
author = {Bouakline, Foudhil and Saalfrank, Peter},
title = {Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics},
series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry},
volume = {154},
journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry},
number = {23},
publisher = {American Institute of Physics},
address = {Melville},
issn = {0021-9606},
doi = {10.1063/5.0049710},
pages = {10},
year = {2021},
abstract = {Recent experiments on laser-dissociation of aligned homonuclear diatomic molecules show an asymmetric forward-backward (spatial) electron-localization along the laser polarization axis. Most theoretical models attribute this asymmetry to interference effects between gerade and ungerade vibronic states. Presumably due to alignment, these models neglect molecular rotations and hence infer an asymmetric (post-dissociation) charge distribution over the two identical nuclei. In this paper, we question the equivalence that is made between spatial electron-localization, observed in experiments, and atomic electron-localization, alluded by these theoretical models. We show that (seeming) agreement between these models and experiments is due to an unfortunate omission of nuclear permutation symmetry, i.e., quantum statistics. Enforcement of the latter requires mandatory inclusion of the molecular rotational degree of freedom, even for perfectly aligned molecules. Unlike previous interpretations, we ascribe spatial electron-localization to the laser creation of a rovibronic wavepacket that involves field-free molecular eigenstates with opposite space-inversion symmetry i.e., even and odd parity. Space-inversion symmetry breaking would then lead to an asymmetric distribution of the (space-fixed) electronic density over the forward and backward hemisphere. However, owing to the simultaneous coexistence of two indistinguishable molecular orientational isomers, our analytical and computational results show that the post-dissociation electronic density along a specified space-fixed axis is equally shared between the two identical nuclei-a result that is in perfect accordance with the principle of the indistinguishability of identical particles. Published under an exclusive license by AIP Publishing.},
language = {en}
}
@article{SchuermannTitovEbeletal.2022,
author = {Sch{\"u}rmann, Robin and Titov, Evgenii and Ebel, Kenny and Kogikoski Junior, Sergio and Mostafa, Amr and Saalfrank, Peter and Milosavljević, Aleksandar R. and Bald, Ilko},
title = {The electronic structure of the metal-organic interface of isolated ligand coated gold nanoparticles},
series = {Nanoscale Advances},
volume = {4},
journal = {Nanoscale Advances},
number = {6},
publisher = {Royal Society of Chemistry},
address = {Cambridge},
issn = {2516-0230},
doi = {10.1039/d1na00737h},
pages = {1599 -- 1607},
year = {2022},
abstract = {Light induced electron transfer reactions of molecules on the surface of noble metal nanoparticles (NPs) depend significantly on the electronic properties of the metal-organic interface. Hybridized metal-molecule states and dipoles at the interface alter the work function and facilitate or hinder electron transfer between the NPs and ligand. X-ray photoelectron spectroscopy (XPS) measurements of isolated AuNPs coated with thiolated ligands in a vacuum have been performed as a function of photon energy, and the depth dependent information of the metal-organic interface has been obtained. The role of surface dipoles in the XPS measurements of isolated ligand coated NPs is discussed and the binding energy of the Au 4f states is shifted by around 0.8 eV in the outer atomic layers of 4-nitrothiophenol coated AuNPs, facilitating electron transport towards the molecules. Moreover, the influence of the interface dipole depends significantly on the adsorbed ligand molecules. The present study paves the way towards the engineering of the electronic properties of the nanoparticle surface, which is of utmost importance for the application of plasmonic nanoparticles in the fields of heterogeneous catalysis and solar energy conversion.},
language = {en}
}
@article{FischerWertherBouaklineetal.2022,
author = {Fischer, Eric Wolfgang and Werther, Michael and Bouakline, Foudhil and Grossmann, Frank and Saalfrank, Peter},
title = {Non-Markovian vibrational relaxation dynamics at surfaces},
series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
volume = {156},
journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
number = {21},
publisher = {AIP Publishing},
address = {Melville},
issn = {0021-9606},
doi = {10.1063/5.0092836},
pages = {16},
year = {2022},
abstract = {Vibrational dynamics of adsorbates near surfaces plays both an important role for applied surface science and as a model lab for studying fundamental problems of open quantum systems. We employ a previously developed model for the relaxation of a D-Si-Si bending mode at a D:Si(100)-(2 x 1) surface, induced by a "bath " of more than 2000 phonon modes [Lorenz and P. Saalfrank, Chem. Phys. 482, 69 (2017)], to extend previous work along various directions. First, we use a Hierarchical Effective Mode (HEM) model [Fischer et al., J. Chem. Phys. 153, 064704 (2020)] to study relaxation of higher excited vibrational states than hitherto done by solving a high-dimensional system-bath time-dependent Schrodinger equation (TDSE). In the HEM approach, (many) real bath modes are replaced by (much less) effective bath modes. Accordingly, we are able to examine scaling laws for vibrational relaxation lifetimes for a realistic surface science problem. Second, we compare the performance of the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) approach with that of the recently developed coherent-state-based multi-Davydov-D2 Ansatz [Zhou et al., J. Chem. Phys. 143, 014113 (2015)]. Both approaches work well, with some computational advantages for the latter in the presented context. Third, we apply open-system density matrix theory in comparison with basically "exact " solutions of the multi-mode TDSEs. Specifically, we use an open-system Liouville-von Neumann (LvN) equation treating vibration-phonon coupling as Markovian dissipation in Lindblad form to quantify effects beyond the Born-Markov approximation. Published under an exclusive license by AIP Publishing.},
language = {en}
}
@article{FischerAndersSaalfrank2022,
author = {Fischer, Eric Wolfgang and Anders, Janet and Saalfrank, Peter},
title = {Cavity-altered thermal isomerization rates and dynamical resonant localization in vibro-polaritonic chemistry},
series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
volume = {156},
journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
number = {15},
publisher = {American Institute of Physics},
address = {Melville, NY},
issn = {0021-9606},
doi = {10.1063/5.0076434},
pages = {16},
year = {2022},
abstract = {It has been experimentally demonstrated that reaction rates for molecules embedded in microfluidic optical cavities are altered when compared to rates observed under "ordinary" reaction conditions. However, precise mechanisms of how strong coupling of an optical cavity mode to molecular vibrations affects the reactivity and how resonance behavior emerges are still under dispute. In the present work, we approach these mechanistic issues from the perspective of a thermal model reaction, the inversion of ammonia along the umbrella mode, in the presence of a single-cavity mode of varying frequency and coupling strength. A topological analysis of the related cavity Born-Oppenheimer potential energy surface in combination with quantum mechanical and transition state theory rate calculations reveals two quantum effects, leading to decelerated reaction rates in qualitative agreement with experiments: the stiffening of quantized modes perpendicular to the reaction path at the transition state, which reduces the number of thermally accessible reaction channels, and the broadening of the barrier region, which attenuates tunneling. We find these two effects to be very robust in a fluctuating environment, causing statistical variations of potential parameters, such as the barrier height. Furthermore, by solving the time-dependent Schrodinger equation in the vibrational strong coupling regime, we identify a resonance behavior, in qualitative agreement with experimental and earlier theoretical work. The latter manifests as reduced reaction probability when the cavity frequency omega(c) is tuned resonant to a molecular reactant frequency. We find this effect to be based on the dynamical localization of the vibro-polaritonic wavepacket in the reactant well.},
language = {en}
}
@article{ReifarthBekirBapolisietal.2022,
author = {Reifarth, Martin and Bekir, Marek and Bapolisi, Alain M. and Titov, Evgenii and Nusshardt, Fabian and Nowaczyk, Julius and Grigoriev, Dmitry and Sharma, Anjali and Saalfrank, Peter and Santer, Svetlana and Hartlieb, Matthias and B{\"o}ker, Alexander},
title = {A dual pH- and light-responsive spiropyrane-based surfactant},
series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition},
volume = {61},
journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition},
number = {21},
publisher = {Wiley-VCH},
address = {Weinheim},
issn = {1433-7851},
doi = {10.1002/anie.202114687},
pages = {10},
year = {2022},
abstract = {A cationic surfactant containing a spiropyrane unit is prepared exhibiting a dual-responsive adjustability of its surface-active characteristics. The switching mechanism of the system relies on the reversible conversion of the non-ionic spiropyrane (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH-dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli-responsive behavior enables remote-control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH-dependent manipulation of oil-in-water emulsions.},
language = {en}
}
@article{TetenoireEhlertJuaristietal.2022,
author = {Tetenoire, Auguste and Ehlert, Christopher and Juaristi, Joseba I{\~n}aki and Saalfrank, Peter and Alducin, Maite},
title = {Why ultrafast photoinduced CO desorption dominates over oxidation on Ru(0001)},
series = {The journal of physical chemistry letters},
volume = {13},
journal = {The journal of physical chemistry letters},
number = {36},
publisher = {American Chemical Society},
address = {Washington, DC},
issn = {1948-7185},
doi = {10.1021/acs.jpclett.2c02327},
pages = {8516 -- 8521},
year = {2022},
abstract = {CO oxidation on Ru(0001) is a long-standing example of a reaction that, being thermally forbidden in ultrahigh vacuum, can be activated by femtosecond laser pulses. In spite of its relevance, the precise dynamics of the photoinduced oxidation process as well as the reasons behind the dominant role of the competing CO photodesorption remain unclear. Here we use ab initio molecular dynamics with electronic friction that account for the highly excited and nonequilibrated system created by the laser to investigate both reactions. Our simulations successfully reproduce the main experimental findings: the existence of photoinduced oxidation and desorption, the large desorption to oxidation branching ratio, and the changes in the O K-edge X-ray absorption spectra attributed to the initial stage of the oxidation process. Now, we are able to monitor in detail the ultrafast CO desorption and CO oxidation occurring in the highly excited system and to disentangle what causes the unexpected inertness to the otherwise energetically favored oxidation.},
language = {en}
}
@article{ChoudhuryDeVineSinhaetal.2022,
author = {Choudhury, Arnab and DeVine, Jessalyn A. A. and Sinha, Shreya and Lau, Jascha Alexander and Kandratsenka, Alexander and Schwarzer, Dirk and Saalfrank, Peter and Wodtke, Alec Michael},
title = {Condensed-phase isomerization through tunnelling gateways},
series = {Nature : the international weekly journal of science},
volume = {612},
journal = {Nature : the international weekly journal of science},
number = {7941},
publisher = {Macmillan Publishers Limited, part of Springer Nature},
address = {London},
issn = {0028-0836},
doi = {10.1038/s41586-022-05451-0},
pages = {691 -- 695},
year = {2022},
abstract = {Quantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave(1). Tunnelling becomes important when the de Broglie wavelength of the particle exceeds the barrier thickness; because wavelength increases with decreasing mass, lighter particles tunnel more efficiently than heavier ones. However, there exist examples in condensed-phase chemistry where increasing mass leads to increased tunnelling rates(2). In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface(3,4), showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling; the energies of these gateways arise nonsystematically, giving an erratic mass dependence. Gateways also accelerate ground-state isomerization, acting as leaky holes through the reaction barrier. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed.},
language = {en}
}
@article{KogikoskiJuniorTapioEdlervonZanderetal.2021,
author = {Kogikoski Junior, Sergio and Tapio, Kosti and Edler von Zander, Robert and Saalfrank, Peter and Bald, Ilko},
title = {Raman enhancement of nanoparticle dimers self-assembled using DNA origami nanotriangles},
series = {Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International},
volume = {26},
journal = {Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International},
number = {6},
publisher = {MDPI},
address = {Basel},
issn = {1420-3049},
doi = {10.3390/molecules26061684},
pages = {18},
year = {2021},
abstract = {Surface-enhanced Raman scattering is a powerful approach to detect molecules at very low concentrations, even up to the single-molecule level. One important aspect of the materials used in such a technique is how much the signal is intensified, quantified by the enhancement factor (EF). Herein we obtained the EFs for gold nanoparticle dimers of 60 and 80 nm diameter, respectively, self-assembled using DNA origami nanotriangles. Cy5 and TAMRA were used as surface-enhanced Raman scattering (SERS) probes, which enable the observation of individual nanoparticles and dimers. EF distributions are determined at four distinct wavelengths based on the measurements of around 1000 individual dimer structures. The obtained results show that the EFs for the dimeric assemblies follow a log-normal distribution and are in the range of 10(6) at 633 nm and that the contribution of the molecular resonance effect to the EF is around 2, also showing that the plasmonic resonance is the main source of the observed signal. To support our studies, FDTD simulations of the nanoparticle's electromagnetic field enhancement has been carried out, as well as calculations of the resonance Raman spectra of the dyes using DFT. We observe a very close agreement between the experimental EF distribution and the simulated values.},
language = {en}
}
@article{WitzorkyParamonovBouaklineetal.2021,
author = {Witzorky, Christoph and Paramonov, Guennaddi and Bouakline, Foudhil and Jaquet, Ralph and Saalfrank, Peter and Klamroth, Tillmann},
title = {Gaussian-type orbital calculations for high harmonic generation in vibrating molecules},
series = {Journal of chemical theory and computation},
volume = {17},
journal = {Journal of chemical theory and computation},
number = {12},
publisher = {American Chemical Society},
address = {Washington},
issn = {1549-9618},
doi = {10.1021/acs.jctc.1c00837},
pages = {7353 -- 7365},
year = {2021},
abstract = {The response of the hydrogen molecular ion, H-2(+), to few-cycle laser pulses of different intensities is simulated. To treat the coupled electron-nuclear motion, we use adiabatic potentials computed with Gaussian-type basis sets together with a heuristic ionization model for the electron and a grid representation for the nuclei. Using this mixed-basis approach, the time-dependent Schrodinger equation is solved, either within the Born-Oppenheimer approximation or with nonadiabatic couplings included. The dipole response spectra are compared to all-grid-based solutions for the three-body problem, which we take as a reference to benchmark the Gaussian-type basis set approaches. Also, calculations employing the fixed-nuclei approximation are performed, to quantify effects due to nuclear motion. For low intensities and small ionization probabilities, we get excellent agreement of the dynamics using Gaussian-type basis sets with the all-grid solutions. Our investigations suggest that high harmonic generation (HHG) and high-frequency response, in general, can be reliably modeled using Gaussian-type basis sets for the electrons for not too high harmonics. Further, nuclear motion destroys electronic coherences in the response spectra even on the time scale of about 30 fs and affects HHG intensities, which reflect the electron dynamics occurring on the attosecond time scale. For the present system, non-Born-Oppenheimer effects are small. The Gaussian-based, nonadiabatically coupled, time-dependent multisurface approach to treat quantum electron-nuclear motion beyond the non-Born-Oppenheimer approximation can be easily extended to approximate wavefunction methods, such as time-dependent configuration interaction singles (TD-CIS), for systems where no benchmarks are available.},
language = {en}
}
@article{RietzeTitovGranuccietal.2020,
author = {Rietze, Clemens and Titov, Evgenii and Granucci, Giovanni and Saalfrank, Peter},
title = {Surface hopping dynamics for azobenzene photoisomerization},
series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
volume = {124},
journal = {The journal of physical chemistry : C, Nanomaterials and interfaces},
number = {48},
publisher = {American Chemical Society},
address = {Washington},
issn = {1932-7447},
doi = {10.1021/acs.jpcc.0c08052},
pages = {26287 -- 26295},
year = {2020},
abstract = {Azobenzenes easily photoswitch in solution, while their photoisomerization at surfaces is often hindered. In recent work, it was demonstrated by nonadiabatic molecular dynamics with trajectory surface hopping [Titov et al., J. Phys. Chem. Lett. 2016, 7, 3591-3596] that the experimentally observed suppression of trans -> cis isomerization yields in azobenzenes in a densely packed SAM (self-assembled monolayer) [Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831-1838] is dominated by steric hindrance. In the present work, we systematically study by ground-state Langevin and nonadiabatic surface hopping dynamics, the effects of decreasing packing density on (i) UV/vis absorption spectra, (ii) trans -> cis isomerization yields, and (iii) excited-state lifetimes of photoexcited azobenzene. Within the quantum mechanics/ molecular mechanics models adopted here, we find that above a packing density of similar to 3 molecules/nm(2), switching yields are strongly reduced, while at smaller packing densities, the "monomer limit" is quickly approached. The UV/vis absorption spectra, on the other hand, depend on packing density over a larger range (down to at least similar to 1 molecule/nm(2)). Trends for excited-state lifetimes are less obvious, but it is found that lifetimes of pi pi* excited states decay monotonically with decreasing coverage. Effects of fluorination of the switches are also discussed for single, free molecules. Fluorination leads to comparatively large trans -> cis yields, in combination with long pi pi* lifetimes. Furthermore, for selected systems, also the effects of n pi* excitation at longer excitation wavelengths have been studied, which is found to enhance trans -> cis yields for free molecules but can lead to an opposite behavior in densely packed SAMs.},
language = {en}
}
@article{FischerWertherBouaklineetal.2020,
author = {Fischer, Eric W. and Werther, Michael and Bouakline, Foudhil and Saalfrank, Peter},
title = {A hierarchical effective mode approach to phonon-driven multilevel vibrational relaxation dynamics at surfaces},
series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry},
volume = {153},
journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry},
number = {6},
publisher = {American Institute of Physics},
address = {Melville},
issn = {0021-9606},
doi = {10.1063/5.0017716},
pages = {15},
year = {2020},
abstract = {We discuss an efficient Hierarchical Effective Mode (HEM) representation of a high-dimensional harmonic oscillator bath, which describes phonon-driven vibrational relaxation of an adsorbate-surface system, namely, deuterium adsorbed on Si(100). Starting from the original Hamiltonian of the adsorbate-surface system, the HEM representation is constructed via iterative orthogonal transformations, which are efficiently implemented with Householder matrices. The detailed description of the HEM representation and its construction are given in the second quantization representation. The hierarchical nature of this representation allows access to the exact quantum dynamics of the adsorbate-surface system over finite time intervals, controllable via the truncation order of the hierarchy. To study the convergence properties of the effective mode representation, we solve the time-dependent Schrodinger equation of the truncated system-bath HEM Hamiltonian, with the help of the multilayer extension of the Multiconfigurational Time-Dependent Hartree (ML-MCTDH) method. The results of the HEM representation are compared with those obtained with a quantum-mechanical tier-model. The convergence of the HEM representation with respect to the truncation order of the hierarchy is discussed for different initial conditions of the adsorbate-surface system. The combination of the HEM representation with the ML-MCTDH method provides information on the time evolution of the system (adsorbate) and multiple effective modes of the bath (surface). This permits insight into mechanisms of vibration-phonon coupling of the adsorbate-surface system, as well as inter-mode couplings of the effective bath.},
language = {en}
}
@article{PenschkeEdlervonZanderBeqirajetal.2022,
author = {Penschke, Christopher and Edler von Zander, Robert and Beqiraj, Alkit and Zehle, Anna and Jahn, Nicolas and Neumann, Rainer and Saalfrank, Peter},
title = {Water on porous, nitrogen-containing layered carbon materials},
series = {Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies / RSC, Royal Society of Chemistry},
volume = {24},
journal = {Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies / RSC, Royal Society of Chemistry},
number = {24},
publisher = {Royal Society of Chemistry},
address = {Cambridge},
issn = {1463-9076},
doi = {10.1039/d2cp00657j},
pages = {14709 -- 14726},
year = {2022},
abstract = {Porous, layered materials containing sp(2)-hybridized carbon and nitrogen atoms, offer through their tunable properties, a versatile route towards tailormade catalysts for electrochemistry and photochemistry. A key molecule interacting with these quasi two-dimensional materials (2DM) is water, and a photo(electro)chemical key reaction catalyzed by them, is water splitting into H-2 and O-2, with the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) as half reactions. The complexity of some C/N-based 2DM in contact with water raises special needs for their theoretical modelling, which in turn is needed for rational design of C/N-based catalysts. In this work, three classes of C/N-containing porous 2DM with varying pore sizes and C/N ratios, namely graphitic carbon nitride (g-C3N4), C2N, and poly(heptazine imides) (PHI), are studied with various computational methods. We elucidate the performance of different models and model chemistries (the combination of electronic structure method and basis set) for water and water fragment adsorption in the low-coverage regime. Further, properties related to the photo(electro)chemical activity like electrochemical overpotentials, band gaps, and optical excitation energies are in our focus. Specifically, periodic models will be tested vs. cluster models, and density functional theory (DFT) vs. wavefunction theory (WFT). This work serves as a basis for a systematic study of trends for the photo(electro)chemical activity of C/N-containing layered materials as a function of water content, pore size and density.},
language = {en}
}
@article{FischerSaalfrank2021,
author = {Fischer, Eric W. and Saalfrank, Peter},
title = {A thermofield-based multilayer multiconfigurational time-dependent Hartree approach to non-adiabatic quantum dynamics at finite temperature},
series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry},
volume = {155},
journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry},
number = {13},
publisher = {American Institute of Physics},
address = {Melville},
issn = {0021-9606},
doi = {10.1063/5.0064013},
pages = {15},
year = {2021},
abstract = {We introduce a thermofield-based formulation of the multilayer multiconfigurational time-dependent Hartree (MCTDH) method to study finite temperature effects on non-adiabatic quantum dynamics from a non-stochastic, wave function perspective. Our approach is based on the formal equivalence of bosonic many-body theory at zero temperature with a doubled number of degrees of freedom and the thermal quasi-particle representation of bosonic thermofield dynamics (TFD). This equivalence allows for a transfer of bosonic many-body MCTDH as introduced by Wang and Thoss to the finite temperature framework of thermal quasi-particle TFD. As an application, we study temperature effects on the ultrafast internal conversion dynamics in pyrazine. We show that finite temperature effects can be efficiently accounted for in the construction of multilayer expansions of thermofield states in the framework presented herein. Furthermore, we find our results to agree well with existing studies on the pyrazine model based on the pMCTDH method.},
language = {en}
}
@article{BedurkeKlamrothSaalfrank2021,
author = {Bedurke, Florian and Klamroth, Tillmann and Saalfrank, Peter},
title = {Many-electron dynamics in laser-driven molecules},
series = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
volume = {23},
journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
number = {24},
publisher = {Royal Society of Chemistry},
address = {Cambridge},
issn = {1463-9076},
doi = {10.1039/d1cp01100f},
pages = {13544 -- 13560},
year = {2021},
abstract = {With recent experimental advances in laser-driven electron dynamics in polyatomic molecules, the need arises for their reliable theoretical modelling. Among efficient, yet fairly accurate methods for many-electron dynamics are Time-Dependent Configuration Interaction Singles (TD-CIS) (a Wave Function Theory (WFT) method), and Real-Time Time-Dependent Density Functional Theory (RT-TD-DFT), respectively. Here we compare TD-CIS combined with extended Atomic Orbital (AO) bases, TD-CIS/AO, with RT-TD-DFT in a grid representation of the Kohn-Sham orbitals, RT-TD-DFT/Grid. Possible ionization losses are treated by complex absorbing potentials in energy space (for TD-CIS/AO) or real space (for RT-TD-DFT), respectively. The comparison is made for two test cases: (i) state-to-state transitions using resonant lasers (pi-pulses), i.e., bound electron motion, and (ii) large-amplitude electron motion leading to High Harmonic Generation (HHG). Test systems are a H-2 molecule and cis- and trans-1,2-dichlorethene, C2H2Cl2, (DCE). From time-dependent electronic energies, dipole moments and from HHG spectra, the following observations are made: first, for bound state-to-state transitions enforced by pi-pulses, TD-CIS nicely accounts for the expected population inversion in contrast to RT-TD-DFT, in agreement with earlier findings. Secondly, when using laser pulses under non-resonant conditions, dipole moments and lower harmonics in HHG spectra are obtained by TD-CIS/AO which are in good agreement with those obtained with RT-TD-DFT/Grid. Deviations become larger for higher harmonics and at low laser intensities, i.e., for low-intensity HHG signals. We also carefully test effects of basis sets for TD-CIS/AO and grid size for RT-TD-DFT/Grid, different exchange-correlation functionals in RT-TD-DFT, and absorbing boundaries. Finally, for the present examples, TD-CIS/AO is observed to be at least an order of magnitude more computationally efficient than RT-TD-DFT/Grid.},
language = {en}
}
@article{TitovSharmaLomadzeetal.2021,
author = {Titov, Evgenii and Sharma, Anjali and Lomadze, Nino and Saalfrank, Peter and Santer, Svetlana and Bekir, Marek},
title = {Photoisomerization of an azobenzene-containing surfactant within a micelle},
series = {ChemPhotoChem},
volume = {5},
journal = {ChemPhotoChem},
number = {10},
publisher = {Wiley-VCH},
address = {Weinheim},
issn = {2367-0932},
doi = {10.1002/cptc.202100103},
pages = {926 -- 932},
year = {2021},
abstract = {Photosensitive azobenzene-containing surfactants have attracted great attention in past years because they offer a means to control soft-matter transformations with light. At concentrations higher than the critical micelle concentration (CMC), the surfactant molecules aggregate and form micelles, which leads to a slowdown of the photoinduced trans -> cis azobenzene isomerization. Here, we combine nonadiabatic dynamics simulations for the surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the reaction slowdown. Our simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles. We also observe a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans -> cis switching in micelles of the azobenzene-containing surfactants.},
language = {en}
}
@article{SinhaSaalfrank2021,
author = {Sinha, Shreya and Saalfrank, Peter},
title = {"Inverted" CO molecules on NaCl(100)},
series = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
volume = {23},
journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
number = {13},
publisher = {Royal Society of Chemistry},
address = {Cambridge},
issn = {1463-9076},
doi = {10.1039/d0cp05198e},
pages = {7860 -- 7874},
year = {2021},
abstract = {Somewhat surprisingly, inverted ("O-down") CO adsorbates on NaCl(100) were recently observed experimentally after infrared vibrational excitation (Lau et al., Science, 2020, 367, 175-178). Here we characterize these species using periodic density functional theory and a quantum mechanical description of vibrations. We determine stationary points and minimum energy paths for CO inversion, for low (1/8 and 1/4 monolayers (ML)) and high (1 ML) coverages. Transition state theory is applied to estimate thermal rates for "C-down" to "O-down" isomerization and the reverse process. For the 1/4 ML p(1 x 1) structure, two-dimensional and three-dimensional potential energy surfaces and corresponding anharmonic vibrational eigenstates obtained from the time-independent nuclear Schrodinger equation are presented. We find (i) rather coverage-independent CO inversion energies (of about 0.08 eV or 8 kJ mol(-1) per CO) and corresponding classical activation energies for "C-down" to "O-down" isomerization (of about 0.15 eV or 14 kJ mol(-1) per CO); (ii) thermal isomerization rates at 22 K which are vanishingly small for the "C-down" to "O-down" isomerization but non-negligible for the back reaction; (iii) several "accidentally degenerate" pairs of eigenstates well below the barrier, each pair describing "C-down" to "O-down" localized states.},
language = {en}
}