TY - JOUR A1 - Herder, Martin A1 - Utecht, Manuel Martin A1 - Manicke, Nicole A1 - Grubert, Lutz A1 - Pätzel, Michael A1 - Saalfrank, Peter A1 - Hecht, Stefan T1 - Switching with orthogonal stimuli electrochemical ring-closure and photochemical ring-opening of bis(thiazolyl) maleimides JF - Chemical science N2 - The photochemistry as well as electrochemistry of novel donor-acceptor bis(morpholinothiazolyl)maleimides has been investigated. Proper substitution of these diarylethene-type molecular switches leads to the unique situation in which their ring-closure can only be accomplished electrochemically, while ring-opening can only be achieved photochemically. Hence, these switches operate with orthogonal stimuli, i.e. redox potential and light, respectively. The switch system could be optimized by introducing trifluoromethyl groups at the reactive carbon atoms in order to avoid by-product formation during oxidative ring closure. Both photochemical and electrochemical pathways were investigated for methylated, trifluoromethylated, and nonsymmetrical bis(morpholinothiazolyl) maleimides as well as the bis(morpholinothiazolyl) cyclopentene reference compound. With the aid of the nonsymmetrical "mixed" derivative, the mechanism of electrochemically driven ring closure could be elucidated and seems to proceed via a dicationic intermediate generated by two-fold oxidation. All experimental work has been complemented by density functional theory that provides detailed insights into the thermodynamics of the ring-open and closed forms, the nature of their excited states, and the reactivity of their neutral as well as ionized species in different electronic configurations. The particular diarylethene systems described herein could serve in multifunctional (logic) devices operated by different stimuli (inputs) and may pave the way to converting light into electrical energy via photoinduced "pumping" of redox-active meta-stable states. Y1 - 2013 U6 - https://doi.org/10.1039/c2sc21681g SN - 2041-6520 VL - 4 IS - 3 SP - 1028 EP - 1040 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10−18 cm2 for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 196 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81198 ER - TY - JOUR A1 - Luo, Ying A1 - Utecht, Manuel Martin A1 - Dokic, Jadranka A1 - Korchak, Sergey A1 - Vieth, Hans-Martin A1 - Haag, Rainer A1 - Saalfrank, Peter T1 - Cis-trans isomerisation of substituted aromatic imines a comparative experimental and theoretical study JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - The cis-trans isomerisation of N-benzylideneaniline (NBA) and derivatives containing a central C=N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans (hv) -> cis isomerisation and the kinetics of the thermal backreaction cis (Delta)-> trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition-state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time-dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify "optimal switches" with good photochromicity and reasonable thermal stability. KW - density functional calculations KW - imines KW - isomerization KW - photochemistry KW - thermochemistry Y1 - 2011 U6 - https://doi.org/10.1002/cphc.201100179 SN - 1439-4235 VL - 12 IS - 12 SP - 2311 EP - 2321 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10(-18) cm(2) for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp03093e SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 27 SP - 18079 EP - 18086 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10−18 cm2 for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp03093e SN - 1463-9076 SN - 1463-9084 VL - 27 IS - 17 SP - 18079 EP - 18086 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Gaebel, Tina A1 - Klamroth, Tillmann T1 - Desorption induced by low energy charge carriers on Si(111)-7 x 7 BT - first principles molecular dynamics for benzene derivates JF - Journal of computational chemistry : organic, inorganic, physical, biological N2 - We use clusters for the modeling of local ion resonances caused by low energy charge carriers in STM-induced desorption of benzene derivates from Si(111)-7 x 7. We perform Born-Oppenheimer molecular dynamics for the charged systems assuming vertical transitions to the charged states at zero temperature, to rationalize the low temperature activation energies, which are found in experiment for chlorobenzene. Our calculations suggest very similar low temperature activation energies for toluene and benzene. For the cationic resonance transitions to physisorption are found even at 0 K, while the anion remains chemisorbed during the propagations. Further, we also extend our previous static quantum chemical investigations to toluene and benzene. In addition, an in depth analysis of the ionization potentials and electron affinities, which are used to estimate resonance energies, is given. KW - Born-Oppenheimer MD KW - STM-induced reactions KW - cluster models KW - Si(111)-7x7 Y1 - 2018 U6 - https://doi.org/10.1002/jcc.25607 SN - 0192-8651 SN - 1096-987X VL - 39 IS - 30 SP - 2517 EP - 2525 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Palmer, Richard E. A1 - Klamroth, Tillmann T1 - Quantum chemical approach to atomic manipulation of chlorobenzene on the Si(111)-7 x 7 surface BT - Resonance localization, vibrational activation, and surface dynamics JF - Physical review materials N2 - We present a cluster model to describe the localization of hot charge carriers on the Si(111)-7 x 7 surface, which leads to (nonlocal) desorption of chlorobenzene molecules in scanning tunneling microscope (STM) manipulation experiments. The localized charge carriers are modeled by a small cluster. By means of quantum chemical calculations, this cluster model explains many experimental findings from STM manipulation. We show that the negative charge is mainly localized in the surface, while the positive one also resides on the molecule. Both resonances boost desorption: In the negative resonance the adatom is elevated; in the positive one the chemisorption bond between the silicon surface adatom and chlorobenzene is broken. We find normal modes promoting desorption matching experimental low-temperature activation energies for electron-and hole-induced desorption. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevMaterials.1.026001 SN - 2475-9953 VL - 1 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Pan, Tianluo A1 - Klamroth, Tillmann A1 - Palmer, Richard E. T1 - Quantum chemical cluster models for chemi- and physisorption of chlorobenzene on Si(111)-7x7 JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - Motivated by recent atomic manipulation experiments, we report quantum chemical calculations for chemi- and physisorption minima of chlorobenzene on the Si(111)-7x7 surface. A density functional theory cluster approach is applied, using the B3LYP hybrid functional alongside Grimme's empirical dispersion corrections (D3). We were able to identify chemisorption sites of binding energies of 1.6 eV and physisorption energies of 0.6 eV, both in encouraging agreement with the trend of experimental data. The cluster approach opens up the possibility of a first-principles based dynamical description of STM manipulation experiments on this system, the interpretation of which involves both the chemi- and physisorbed states. However, we found that special care has to be taken regarding the choice of clusters, basis sets, and the evaluation of the dispersion corrections. Y1 - 2014 U6 - https://doi.org/10.1021/jp504208d SN - 1089-5639 VL - 118 IS - 33 SP - 6699 EP - 6704 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Hänsel, Marc A1 - Barta, Christoph A1 - Rietze, Clemens A1 - Utecht, Manuel Martin A1 - Rueck-Braun, Karola A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Two-Dimensional Nonlinear Optical Switching Materials BT - Molecular Engineering toward High Nonlinear Optical Contrasts JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Combining photochromism and nonlinear optical (NLO) properties of molecular switches-functionalized self-assembled monolayers (SAMs) represents a promising concept toward novel photonic and optoelectronic devices. Using second harmonic generation, density functional theory, and correlated wave function methods, we studied the switching abilities as well as the NLO contrasts between different molecular states of various fulgimide-containing SAMs on Si(111). Controlled variations of the linker systems as well as of the fulgimides enabled us to demonstrate very efficient reversible photoinduced ring-opening/closure reactions between the open and closed forms of the fulgimides. Thus, effective cross sections on the order of 10(-18) cm(-2) are observed. Moreover, the reversible switching is accompanied by pronounced NLO contrasts up to 32%. Further molecular engineering of the photochromic switches and the linker systems may even increase the NLO contrast upon switching. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcc.8b08212 SN - 1932-7447 SN - 1932-7455 VL - 122 IS - 44 SP - 25555 EP - 25564 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Utecht, Manuel Martin A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Based on the analysis of optical absorption spectra, it has recently been speculated that the excitonic coupling between individual azobenzene-functionalized alkanethiols arranged in a self-assembled monolayer (SAM) on a gold surface could be strong enough to hinder collective trans-cis isomerization-on top of steric hindrance [Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831]. Using models of SAMs of increasing complexity (dimer, linear N-mers, and two-dimensionally arranged N-mers) and density functional theory on the (TD-) B3LYP/6-31G* level, we determine optical absorption spectra, the nature and magnitude of excitonic couplings, and the corresponding spectral shifts. It is found that at inter-monomer distances of about 20 angstrom and above, TD-B3LYP excitation frequencies (and signal intensities) can be well described by the frequently used point-dipole approximation. Further, calculated blue shifts in optical absorption spectra account for the experimental observations made for azobenzene/gold SAMs, and hint to the fact that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures. Y1 - 2011 U6 - https://doi.org/10.1039/c1cp22793a SN - 1463-9076 VL - 13 IS - 48 SP - 21608 EP - 21614 PB - Royal Society of Chemistry CY - Cambridge ER -