TY  - JOUR
A1  - Titov, Evgenii
A1  - Kopp, Tristan
A1  - Hoche, Joscha
A1  - Humeniuk, Alexander
A1  - Mitrić, Roland
T1  - (De)localization dynamics of molecular excitons
BT  - comparison of mixed quantum-classical and fully quantum treatments
JF  - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies
N2  - Molecular excitons play a central role in processes of solar energy conversion, both natural and artificial. It is therefore no wonder that numerous experimental and theoretical investigations in the last decade, employing state-of-the-art spectroscopic techniques and computational methods, have been driven by the common aim to unravel exciton dynamics in multichromophoric systems. Theoretically, exciton (de)localization and transfer dynamics are most often modelled using either mixed quantum-classical approaches (e.g., trajectory surface hopping) or fully quantum mechanical treatments (either using model diabatic Hamiltonians or direct dynamics). Yet, the terms such as "exciton localization" or "exciton transfer" may bear different meanings in different works depending on the method in use (quantum-classical vs. fully quantum). Here, we relate different views on exciton (de)localization. For this purpose, we perform molecular surface hopping simulations on several tetracene dimers differing by a magnitude of exciton coupling and carry out quantum dynamical as well as surface hopping calculations on a relevant model system. The molecular surface hopping simulations are done using efficient long-range corrected time-dependent density functional tight binding electronic structure method, allowing us to gain insight into different regimes of exciton dynamics in the studied systems.
Y1  - 2022
U6  - https://doi.org/10.1039/d2cp00586g
SN  - 1463-9076
SN  - 1463-9084
VL  - 24
IS  - 20
SP  - 12136
EP  - 12148
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Kulesza, Alexander Jan
A1  - Titov, Evgenii
A1  - Daly, Steven
A1  - Wlodarczyk, Radoslaw
A1  - Megow, Jörg
A1  - Saalfrank, Peter
A1  - Choi, Chang Min
A1  - MacAleese, Luke
A1  - Antoine, Rodolphe
A1  - Dugourd, Philippe
T1  - Excited States of Xanthene Analogues: Photofragmentation and Calculations by CC2 and Time-Dependent Density Functional Theory
JF  - ChemPhysChem : a European journal of chemical physics and physical chemistry
N2  - Action spectroscopy has emerged as an analytical tool to probe excited states in the gas phase. Although comparison of gas-phase absorption properties with quantum-chemical calculations is, in principle, straightforward, popular methods often fail to describe many molecules of interest-such as xanthene analogues. We, therefore, face their nano-and picosecond laser-induced photofragmentation with excited-state computations by using the CC2 method and time-dependent density functional theory (TDDFT). Whereas the extracted absorption maxima agree with CC2 predictions, the TDDFT excitation energies are blueshifted. Lowering the amount of Hartree-Fock exchange in the DFT functional can reduce this shift but at the cost of changing the nature of the excited state. Additional bandwidth observed in the photofragmentation spectra is rationalized in terms of multiphoton processes. Observed fragmentation from higher-lying excited states conforms to intense excited-to-excited state transitions calculated with CC2. The CC2 method is thus suitable for the comparison with photofragmentation in xanthene analogues.
KW  - density functional calculations
KW  - CC2 calculations
KW  - multiphoton processes
KW  - photofragmentation
KW  - xanthenes
Y1  - 2016
U6  - https://doi.org/10.1002/cphc.201600650
SN  - 1439-4235
SN  - 1439-7641
VL  - 17
SP  - 3129
EP  - 3138
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Titov, Evgenii
A1  - Granucci, Giovanni
A1  - Goetze, Jan Philipp
A1  - Persico, Maurizio
A1  - Saalfrank, Peter
T1  - Dynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric Effects
JF  - The journal of physical chemistry letters
N2  - While azobenzenes readily photoswitch in solution, their photoisomerization in densely packed self-assembled monolayers (SAMs) can be suppressed. Reasons for this can be steric hindrance and/or electronic quenching, e.g., by exciton coupling. We address these possibilities by means of nonadiabatic molecular dynamics with trajectory surface hopping calculations, investigating the trans -> cis isomerization of azobenzene after excitation into the pi pi* absorption band. We consider a free monomer, an isolated dimer and a dimer embedded in a SAM-like environment of additional azobenzene molecules, imitating in this way the gradual transition from an unconstrained over an electronically coupled to an electronically coupled and sterically hindered, molecular switch. Our simulations reveal that in comparison to the single molecule the quantum yield of the trans -> cis photoisomerization is similar for the isolated dimer, but greatly reduced in the sterically constrained situation. Other implications of dimerization and steric constraints are also discussed.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.jpciett.6b01401
SN  - 1948-7185
VL  - 7
SP  - 3591
EP  - 3596
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Goulet-Hanssens, Alexis
A1  - Rietze, Clemens
A1  - Titov, Evgenii
A1  - Abdullahu, Leonora
A1  - Grubert, Lutz
A1  - Saalfrank, Peter
A1  - Hecht, Stefan
T1  - Hole Catalysis as a General Mechanism for Efficient and Wavelength-Independent Z -> E Azobenzene Isomerization
JF  - CHEM
N2  - Whereas the reversible reduction of azobenzenes has been known for decades, their oxidation is destructive and as a result has been notoriously overlooked. Here, we show that a chain reaction leading to quantitative Z -> E isomerization can be initiated before reaching the destructive anodic peak potential. This hole-catalyzed pathway is accessible to all azobenzenes, without exception, and offers tremendous advantages over the recently reported reductive, radical-anionic pathway because it allows for convenient chemical initiation without the need for electrochemical setups and in the presence of air. In addition, catalytic amounts of metal-free sensitizers, such as methylene blue, can be used as excited-state electron acceptors, enabling a shift of the excitation wavelength to the far red of the azobenzene absorption (up to 660 nm) and providing quantum yields exceeding unity (up to 200%). Our approach will boost the efficiency and sensitivity of optically dense liquid-crystalline and solid photo-switchable materials.
Y1  - 2018
U6  - https://doi.org/10.1016/j.chempr.2018.06.002
SN  - 2451-9294
VL  - 4
IS  - 7
SP  - 1740
EP  - 1755
PB  - Cell Press
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Schürmann, Robin
A1  - Titov, Evgenii
A1  - Ebel, Kenny
A1  - Kogikoski Junior, Sergio
A1  - Mostafa, Amr
A1  - Saalfrank, Peter
A1  - Milosavljević, Aleksandar R.
A1  - Bald, Ilko
T1  - The electronic structure of the metal-organic interface of isolated ligand coated gold nanoparticles
JF  - Nanoscale Advances
N2  - 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.
Y1  - 2022
U6  - https://doi.org/10.1039/d1na00737h
SN  - 2516-0230
VL  - 4
IS  - 6
SP  - 1599
EP  - 1607
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Kuntze, Kim
A1  - Viljakka, Jani
A1  - Titov, Evgenii
A1  - Ahmed, Zafar
A1  - Kalenius, Elina
A1  - Saalfrank, Peter
A1  - Priimagi, Arri
T1  - Towards low-energy-light-driven bistable photoswitches
BT  - ortho-fluoroaminoazobenzenes
JF  - Photochemical & photobiological sciences / European Society for Photobiology
N2  - 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. <br /> [GRAPHICS] <br /> .
Y1  - 2022
U6  - https://doi.org/10.1007/s43630-021-00145-4
SN  - 1474-905X
SN  - 1474-9092
VL  - 21
IS  - 2
SP  - 159
EP  - 173
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Zakrevskyy, Yuriy
A1  - Titov, Evgenii
A1  - Lomadze, Nino
A1  - Santer, Svetlana
T1  - Phase diagrams of DNA-photosensitive surfactant complexes: Effect of ionic strength and surfactant structure
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Realization of all-optically controlled and efficient DNA compaction is the major motivation in the study of interactions between DNA and photosensitive surfactants. In this article, using recently published approach of phase diagram construction [Y. Zakrevskyy, P. Cywinski, M. Cywinska, J. Paasche, N. Lomadze, O. Reich, H.-G. Lohmannsroben, and S. Santer, J. Chem. Phys. 140, 044907 (2014)], a strategy for substantial reduction of compaction agent concentration and simultaneous maintaining the light-induced decompaction efficiency is proposed. The role of ionic strength (NaCl concentration), as a very important environmental parameter, and surfactant structure (spacer length) on the changes of positions of phase transitions is investigated. Increase of ionic strength leads to increase of the surfactant concentration needed to compact DNA molecule. However, elongation of the spacer results to substantial reduction of this concentration. DNA compaction by surfactants with longer tails starts to take place in diluted solutions at charge ratios Z < 1 and is driven by azobenzene-aggregation compaction mechanism, which is responsible for efficient decompaction. Comparison of phase diagrams for different DNA-photosensitive surfactant systems allowed explanation and proposal of a strategy to overcome previously reported limitations of the light-induced decompaction for complexes with increasing surfactant hydrophobicity. (C) 2014 AIP Publishing LLC.
Y1  - 2014
U6  - https://doi.org/10.1063/1.4899281
SN  - 0021-9606
SN  - 1089-7690
VL  - 141
IS  - 16
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Titov, Evgenii
A1  - Lysyakova, Liudmila
A1  - Lomadze, Nino
A1  - Kabashin, Andrei V.
A1  - Saalfrank, Peter
A1  - Santer, Svetlana
T1  - Thermal Cis-to-Trans Isomerization of Azobenzene-Containing Molecules Enhanced by Gold Nanoparticles: An Experimental and Theoretical Study
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - We report on the experimental and theoretical investigation of a considerable increase in the rate for thermal cis -> trans isomerization of azobenzene-containing molecules in the presence of gold nanopartides. Experimentally, by means of UV vis spectroscopy, we studied a series of azobenzene-containing surfactants and 4-nitroazobenzene. We found that in the presence of gold,nanoparticles the thermal lifetime of the cis isomer of the azobenzenecontaining molecules was decreased by up to 3 orders of magnitude in comparison to the lifetime in solution without nanoparticles. The electron transfer between azobenzene-containing molecules and a surface of gold nanopartides is a possible reason to promote the thermal cis trans switching. To investigate the effect of electron attachment to, and withdrawal from, the azobenzene-containing molecules on the isomerization rate, we performed density functional theory calculations of activation energy barriers of the reaction together with Eyring's transition state theory calculations of the rates for azobenzene derivatives with donor and acceptor groups in para position of one of the phenyl rings, as well as for one of the azobenzene-containing surfactants. We found that activation barriers are greatly lowered for azobenzene-containing molecules, both upon electron attachment and withdrawal, which leads, in turn, to a dramatic increase in the thermal isomerization rate.
Y1  - 2015
U6  - https://doi.org/10.1021/acs.jpcc.5b02473
SN  - 1932-7447
VL  - 119
IS  - 30
SP  - 17369
EP  - 17377
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Titov, Evgenii
T1  - On the low-lying electronically excited states of azobenzene dimers
BT  - Transition density matrix analysis
JF  - Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International
N2  - Azobenzene-containing molecules may associate with each other in systems such as self-assembled monolayers or micelles. The interaction between azobenzene units leads to a formation of exciton states in these molecular assemblies. Apart from local excitations of monomers, the electronic transitions to the exciton states may involve charge transfer excitations. Here, we perform quantum chemical calculations and apply transition density matrix analysis to quantify local and charge transfer contributions to the lowest electronic transitions in azobenzene dimers of various arrangements. We find that the transitions to the lowest exciton states of the considered dimers are dominated by local excitations, but charge transfer contributions become sizable for some of the lowest pi pi* electronic transitions in stacked and slip-stacked dimers at short intermolecular distances. In addition, we assess different ways to partition the transition density matrix between fragments. In particular, we find that the inclusion of the atomic orbital overlap has a pronounced effect on quantifying charge transfer contributions if a large basis set is used.
KW  - azobenzene
KW  - dimer
KW  - transition density matrix
KW  - exciton
KW  - charge transfer
KW  - excited states
KW  - TD-DFT
KW  - ADC(2)
Y1  - 2021
U6  - https://doi.org/10.3390/molecules26144245
SN  - 1420-3049
VL  - 26
IS  - 14
PB  - MDPI
CY  - Basel
ER  - 
TY  - THES
A1  - Titov, Evgenii
T1  - Quantum chemistry and surface hopping dynamics of azobenzenes
T1  - Quantenchemie und Surface Hopping Dynamik von Azobenzolen
BT  - free and constrained models
BT  - freie und eingeschränkte Modelle
N2  - This cumulative doctoral dissertation, based on three publications, is devoted to the investigation of several aspects of azobenzene molecular switches, with the aid of computational chemistry.
In the first paper, the isomerization rates of a thermal cis → trans isomerization of azobenzenes for species formed upon an integer electron transfer, i.e., with added or removed electron, are calculated from Eyring’s transition state theory and activation energy barriers, computed by means of density functional theory. The obtained results are discussed in connection with an experimental study of the thermal cis → trans isomerization of azobenzene derivatives in the presence of gold nanoparticles, which is demonstrated to be greatly accelerated in comparison to the same isomerization reaction in the absence of nanoparticles.
The second paper is concerned with electronically excited states of (i) dimers, composed of two photoswitchable units placed closely side-by-side, as well as (ii) monomers and dimers adsorbed on a silicon cluster. A variety of quantum chemistry methods, capable of calculating molecular electronic absorption spectra, based on density functional and wave function theories, is employed to quantify changes in optical absorption upon dimerization and covalent grafting to a surface. Specifically, the exciton (Davydov) splitting between states of interest is determined from first-principles calculations with the help of natural transition orbital analysis, allowing for insight into the nature of excited states.
In the third paper, nonadiabatic molecular dynamics with trajectory surface hopping is applied to model the photoisomerization of azobenzene dimers, (i) for the isolated case (exhibiting the exciton coupling between two molecules) as well as (ii) for the constrained case (providing the van der Waals interaction with environment in addition to the exciton coupling between two monomers). For the latter, the additional azobenzene molecules, surrounding the dimer, are introduced, mimicking a densely packed self-assembled monolayer. From obtained results it is concluded that the isolated dimer is capable of isomerization likewise the monomer, whereas the steric hindrance considerably suppresses trans → cis photoisomerization.
Furthermore, the present dissertation comprises the general introduction describing the main features of the azobenzene photoswitch and objectives of this work, theoretical basis of the employed methods, and discussion of gained findings in the light of existing literature. Also, additional results on (i) activation parameters of the thermal cis → trans isomerization of azobenzenes, (ii) an approximate scheme to account for anharmonicity of molecular vibrations in calculation of the activation entropy, as well as (iii) absorption spectra of photoswitch–silicon composites obtained from time-demanding wave function-based methods are presented.
N2  - Die vorliegende kumulative Dissertationsschrift basiert auf drei wissenschaftlichen Publikationen und beschäftigt sich mit der computerchemischen Erforschung von molekularen Azobenzol-Schaltern.
Die erste Publikation behandelt die thermische cis → trans Isomerisierung von Azobenzol durch einen Elektronentransfer (ein Elektron wird hinzugefügt oder entnommen). Dabei ist die Berechnung der Isomerisierungsrate des Elektronenübergangs nach der Eyringschen Theorie des Übergangszustands unter Einsatz von Aktivierungsenenergien durchgeführt worden. Die Letzteren sind mittels Dichtefunktionaltheorie berechnet worden. Die daraus erhaltenen Ergebnisse sind in Zusammenhang mit experimentellen Untersuchungen der thermische cis → trans Isomerisierung von Azobenzol-Derivaten in Lösung mit und ohne Goldnanopartikeln diskutiert worden. Die thermische Isomerisierung in Anwesenheit der Goldnanopartikeln läuft stark beschleunigt ab.
Die zweite Publikation beschäftigt sich mit elektronisch angeregten Zuständen von (i) Dimeren bestehend aus zwei schaltbaren Einheiten, die dicht nebeneinander platziert sind, sowie (ii) Monomeren und Dimeren, die an einen Siliziumcluster adsorbiert sind. Mehrere quantenchemische Methoden basierend auf Dichtefunktionaltheorie und Wellenfunktionstheorie sind zur Berechnung der molekularen elektronischen Absorptionsspektren verwendet worden. Dadurch sind die Änderungen in der optischen Absorption sowohl bei der Dimerisierung, als auch beim kovalenten Anbinden an die Oberfläche bestimmt worden. Dazu ist die exzitonische Aufspaltung (Davydov splitting) zwischen den angeregten Zuständen aus ersten Prinzipien unter Verwendung von speziellen Orbitalen für Übergangszustände (natural transition orbitals) berechnet worden. Dadurch wird ein Einblick in die Natur der angeregten Zuständen erreicht. In der dritten Publikation ist eine nicht-adiabatische Molekulardynamik-Simulation unter Anwendung von trajectory surface hopping durchgeführt worden, um die Photoisomerisirung von Azobenzol-Dimeren zu modellieren. Dabei sind (i) ein isoliertes sowie (ii) ein Dimer in der Monolage betrachtet worden. Es sind die exzitonische Kopplung zwischen den zwei Molekülen, sowie, im Falle der Monolage, auch Van-der-Waals-Wechselwirkungen berücksicht worden. Die Ergebnisse weisen darauf hin, dass ein isoliertes Dimer gleichermaßen isomerisierungsfähig wie ein Monomer ist, wobei die cis → trans Photoisomerisierung durch die sterische Hinderung erheblich unterdrückt wird.
Außerdem beinhaltet die darliegende Dissertationsschrift eine allgemeine Einführung, theoretische Grundlagen der verwendeten Methoden und die Diskussion der erhaltenen Ergebnisse mit Blick auf die vorhandene Literatur. Ferner sind zusätzliche Ergebnisse bezüglich der folgenden Aspekte dargestellt: (i) Aktivierungsparameter der thermischen cis → trans Isomerisierung von Azobenzol; (ii) ein Näherungsverfahren zur Berücksichtigung der Anharmonizität von Molekülschwingungen bei Berechnung der Aktivierungsentropie; (iii) Absorptionspektren von Photoschalter-Silizium-Kompositen berechnet mithilfe von zeitaufwändigen Wellenfunktions-basierten Methoden.
KW  - quantum chemistry
KW  - surface hopping dynamics
KW  - azobenzene
KW  - Quantenchemie
KW  - Surface Hopping Dynamik
KW  - Azobenzol
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394610
ER  - 
TY  - JOUR
A1  - Rietze, Clemens
A1  - Titov, Evgenii
A1  - Granucci, Giovanni
A1  - Saalfrank, Peter
T1  - Surface hopping dynamics for azobenzene photoisomerization
BT  - effects of packing density on surfaces, fluorination, and excitation wavelength
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - 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.
KW  - Computational chemistry
KW  - Energy
KW  - Molecules
KW  - Monomers
KW  - Oligomers
Y1  - 2020
U6  - https://doi.org/10.1021/acs.jpcc.0c08052
SN  - 1932-7447
SN  - 1932-7455
VL  - 124
IS  - 48
SP  - 26287
EP  - 26295
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Titov, Evgenii
A1  - Saalfrank, Peter
T1  - Exciton Splitting of Adsorbed and Free 4-Nitroazobenzene Dimers: A Quantum Chemical Study
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - Molecular photoswitches such as azobenzenes, which undergo photochemical trans <-> cis isomerizations, are often mounted for possible applications on a surface and/or surrounded by other switches, for example, in self-assembled monolayers. This may suppress the isomerization cross section due to possible steric reasons, or, as recently speculated, by exciton coupling to. neighboring switches, leading to ultrafast electronic quenching (Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831). The presence of exciton coupling has been anticipated from a blue shift of the optical absorption band, compared to molecules in solution. From the theory side the need arises to properly analyze and quantify the change of absorption spectra of interacting and adsorbed switches. In particular, suitable methods should be identified, and effects of intermolecule and molecule surface interactions on spectra should be disentangled. In this paper by means of time-dependent Hartree-Fock. (TD-HF), various flavors of time-dependent density functional theory (TD-DFT), and the correlated wave function based, coupled cluster (CC2) method we investigated the 4-nitroazobenzene molecule as an:example: The low-lying singlet excited states in the isolated trans monomer and dieter as well as their composites with a silicon pentamantane nanocluster, which serves also as a crude model for a silicon surface, were determined. As most important results we found that (i) HF, CC2, range-separated density functionals, or global hybrids with large amount of exact exchange are able to describe exciton (Davydov) splitting properly, while hybrids with small amount of exact exchange fail producing spurious charge transfer. (ii) The exciton splitting in a free dimer would lead to a blue shift of the absorption signal; however, this effect is almost nullified or even overcompensated by the shift arising from van der Waals interactions between the two molecules. (iii) Adsorption on the Si "surface" leads to a further, strong red shift for the present system. (iv) At a next-nearest neighbor distance (of similar to 3.6 angstrom), the exciton splitting is similar to 0.3 eV, with or without "surface", suggesting a rapid quenching of the molecular pi ->pi* excitation. At larger distances, exciton splitting decreases rapidly.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.jpca.5b10376
SN  - 1089-5639
VL  - 120
SP  - 3055
EP  - 3070
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Goulet-Hanssens, Alexis
A1  - Utecht, Manuel
A1  - Mutruc, Dragos
A1  - Titov, Evgenii
A1  - Schwarz, Jutta
A1  - Grubert, Lutz
A1  - Bleger, David
A1  - Saalfrank, Peter
A1  - Hecht, Stefan
T1  - Electrocatalytic Z -> E Isomerization of Azobenzenes
JF  - Journal of the American Chemical Society
N2  - A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z -> E) by the same wavelength of light, which normally triggers E -> Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.
Y1  - 2017
U6  - https://doi.org/10.1021/jacs.6b10822
SN  - 0002-7863
VL  - 139
IS  - 1
SP  - 335
EP  - 341
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kasyanenko, Nina
A1  - Lysyakova, Liudmila
A1  - Ramazanov, Ruslan
A1  - Nesterenko, Alexey
A1  - Yaroshevich, Igor
A1  - Titov, Evgenii
A1  - Alexeev, G.
A1  - Lezov, Andrey
A1  - Unksov, I.
T1  - Conformational and Phase Transitions in DNA-Photosensitive Surfactant Solutions: Experiment and Modeling
JF  - Biopolymers
N2  - DNA binding to trans- and cis-isomers of azobenzene containing cationic surfactant in 5 mM NaCl solution was investigated by the methods of dynamic light scattering (DLS), low-gradient viscometry (LGV), atomic force microscopy (AFM), circular dichroism (CD), gel electrophoresis (GE), flow birefringence (FB), UV-Vis spectrophotometry. Light-responsive conformational transitions of DNA in complex with photosensitive surfactant, changes in DNA optical anisotropy and persistent length, phase transition of DNA into nanoparticles induced by high surfactant concentration, as well as transformation of surfactant conformation under its binding to macromolecule were studied. Computer simulations of micelles formation for cis- and trans-isomers of azobenzene containing surfactant, as well as DNA-surfactant interaction, were carried out. Phase diagram for DNA-surfactant solutions was designed. The possibility to reverse the DNA packaging induced by surfactant binding with the dilution and light irradiation was shown. (c) 2014 Wiley Periodicals, Inc. Biopolymers 103: 109-122, 2015.
KW  - DNA-surfactant complexes
KW  - light-induced DNA de-compaction
KW  - phase diagram
KW  - DNA volume and persistent length
Y1  - 2015
U6  - https://doi.org/10.1002/bip.22575
SN  - 0006-3525
SN  - 1097-0282
VL  - 103
IS  - 2
SP  - 109
EP  - 122
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Rietze, Clemens
A1  - Titov, Evgenii
A1  - Lindner, Steven
A1  - Saalfrank, Peter
T1  - Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory
JF  - Journal of physics : Condensed matter
N2  - The thermal Z -> E (back-) isomerization of azobenzenes is a prototypical reaction occurring in molecular switches. It has been studied for decades, yet its kinetics is not fully understood. In this paper, quantum chemical calculations are performed to model the kinetics of an experimental benchmark system, where a modified azobenzene (AzoBiPyB) is embedded in a metal-organic framework (MOF). The molecule can be switched thermally from cis to trans, under solvent-free conditions. We critically test the validity of Eyring transition state theory for this reaction. As previously found for other azobenzenes (albeit in solution), good agreement between theory and experiment emerges for activation energies and activation free energies, already at a comparatively simple level of theory, B3LYP/6-31G* including dispersion corrections. However, theoretical Arrhenius prefactors and activation entropies are in qualitiative disagreement with experiment. Several factors are discussed that may have an influence on activation entropies, among them dynamical and geometric constraints (imposed by the MOF). For a simpler model-Z -> E isomerization in azobenzene-a systematic test of quantum chemical methods from both density functional theory and wavefunction theory is carried out in the context of Eyring theory. Also, the effect of anharmonicities on activation entropies is discussed for this model system. Our work highlights capabilities and shortcomings of Eyring transition state theory and quantum chemical methods, when applied for the Z -> E (back-) isomerization of azobenzenes under solvent-free conditions.
KW  - thermal isomerization
Y1  - 2017
U6  - https://doi.org/10.1088/1361-648X/aa75bd
SN  - 0953-8984
SN  - 1361-648X
VL  - 29
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Reifarth, Martin
A1  - Bekir, Marek
A1  - Bapolisi, Alain M.
A1  - Titov, Evgenii
A1  - Nusshardt, Fabian
A1  - Nowaczyk, Julius
A1  - Grigoriev, Dmitry
A1  - Sharma, Anjali
A1  - Saalfrank, Peter
A1  - Santer, Svetlana
A1  - Hartlieb, Matthias
A1  - Böker, Alexander
T1  - A dual pH- and light-responsive spiropyrane-based surfactant
BT  - investigations on Its switching behavior and remote control over emulsion stability
JF  - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition
N2  - 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.
KW  - Dual-Responsiveness
KW  - Manipulation of Emulsion Stability
KW  - Spiropyrane
KW  - Surfactant
KW  - Switchable Surfactants
KW  - pH-Dependent Photoresponsivity
Y1  - 2022
U6  - https://doi.org/10.1002/anie.202114687
SN  - 1433-7851
SN  - 1521-3773
VL  - 61
IS  - 21
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Titov, Evgenii
A1  - Sharma, Anjali
A1  - Lomadze, Nino
A1  - Saalfrank, Peter
A1  - Santer, Svetlana
A1  - Bekir, Marek
T1  - Photoisomerization of an azobenzene-containing surfactant within a micelle
JF  - ChemPhotoChem
N2  - 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.
KW  - azobenzene
KW  - micelles
KW  - photoswitches
KW  - rate constants
KW  - surfactants
KW  - surface hopping
Y1  - 2021
U6  - https://doi.org/10.1002/cptc.202100103
SN  - 2367-0932
VL  - 5
IS  - 10
SP  - 926
EP  - 932
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Malyar, Ivan V.
A1  - Titov, Evgenii
A1  - Lomadze, Nino
A1  - Saalfrank, Peter
A1  - Santer, Svetlana
T1  - Photoswitching of azobenzene-containing self-assembled monolayers as a tool for control over silicon surface electronic properties
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - We report on photoinduced remote control of work function and surface potential of a silicon surface modified with a photosensitive self-assembled monolayer consisting of chemisorbed azobenzene molecules (4-nitroazobenzene). Itwas found that the attachment of the organic monolayer increases the work function by hundreds of meV due to the increase in the electron affinity of silicon substrates. The change in the work function on UV light illumination is more pronounced for the azobenzene jacketed silicon substrate (ca. 250 meV) in comparison to 50 meV for the unmodified surface. Moreover, the photoisomerization of azobenzene results in complex kinetics of thework function change: immediate decrease due to light-driven processes in the silicon surface followed by slower recovery to the initial state due to azobenzene isomerization. This behavior could be of interest for electronic devices where the reaction on irradiation should be more pronounced at small time scales but the overall surface potential should stay constant over time independent of the irradiation conditions. Published by AIP Publishing.
Y1  - 2017
U6  - https://doi.org/10.1063/1.4978225
SN  - 0021-9606
SN  - 1089-7690
VL  - 146
PB  - American Institute of Physics
CY  - Melville
ER  -