@article{UtechtGaebelKlamroth2018, author = {Utecht, Manuel Martin and Gaebel, Tina and Klamroth, Tillmann}, title = {Desorption induced by low energy charge carriers on Si(111)-7 x 7}, series = {Journal of computational chemistry : organic, inorganic, physical, biological}, volume = {39}, journal = {Journal of computational chemistry : organic, inorganic, physical, biological}, number = {30}, publisher = {Wiley}, address = {Hoboken}, issn = {0192-8651}, doi = {10.1002/jcc.25607}, pages = {2517 -- 2525}, year = {2018}, abstract = {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.}, language = {en} } @article{HaenselBartaRietzeetal.2018, author = {H{\"a}nsel, Marc and Barta, Christoph and Rietze, Clemens and Utecht, Manuel Martin and Rueck-Braun, Karola and Saalfrank, Peter and Tegeder, Petra}, title = {Two-Dimensional Nonlinear Optical Switching Materials}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {122}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {44}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b08212}, pages = {25555 -- 25564}, year = {2018}, abstract = {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.}, language = {en} } @article{UtechtPalmerKlamroth2017, author = {Utecht, Manuel Martin and Palmer, Richard E. and Klamroth, Tillmann}, title = {Quantum chemical approach to atomic manipulation of chlorobenzene on the Si(111)-7 x 7 surface}, series = {Physical review materials}, volume = {1}, journal = {Physical review materials}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {2475-9953}, doi = {10.1103/PhysRevMaterials.1.026001}, pages = {5}, year = {2017}, abstract = {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.}, language = {en} } @misc{SchulzeUtechtMoldtetal.2015, author = {Schulze, Michael and Utecht, Manuel Martin and Moldt, Thomas and Przyrembel, Daniel and Gahl, Cornelius and Weinelt, Martin and Saalfrank, Peter and Tegeder, Petra}, title = {Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-81198}, year = {2015}, abstract = {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.}, language = {en} } @article{SchulzeUtechtMoldtetal.2015, author = {Schulze, Michael and Utecht, Manuel Martin and Moldt, Thomas and Przyrembel, Daniel and Gahl, Cornelius and Weinelt, Martin and Saalfrank, Peter and Tegeder, Petra}, title = {Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {17}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {27}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c5cp03093e}, pages = {18079 -- 18086}, year = {2015}, abstract = {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.}, language = {en} } @article{SchulzeUtechtHebertetal.2015, author = {Schulze, Michael and Utecht, Manuel Martin and Hebert, Andreas and R{\"u}ck-Braun, Karola and Saalfrank, Peter and Tegeder, Petra}, title = {Reversible Photoswitching of the Interfacial Nonlinear Optical Response}, series = {The journal of physical chemistry letters}, volume = {6}, journal = {The journal of physical chemistry letters}, number = {3}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz502477m}, pages = {505 -- 509}, year = {2015}, abstract = {Incorporating photochromic molecules into organic/inorganic hybrid materials may lead to photoresponsive systems. In such systems, the second-order nonlinear properties can be controlled via external stimulation with light at an appropriate wavelength. By creating photochromic molecular switches containing self-assembled monolayers on Si(111), we can demonstrate efficient reversible switching, which is accompanied by a pronounced modulation of the nonlinear optical (NLO) response of the system. The concept of utilizing functionalized photoswitchable Si surfaces could be a way for the generation of two-dimensional NLO switching materials, which are promising for applications in photonic and optoelectronic devices.}, language = {en} } @article{SchulzeUtechtMoldtetal.2015, author = {Schulze, Michael and Utecht, Manuel Martin and Moldt, Thomas and Przyrembel, Daniel and Gahl, Cornelius and Weinelt, Martin and Saalfrank, Peter and Tegeder, Petra}, title = {Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers}, series = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, volume = {27}, journal = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, number = {17}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c5cp03093e}, pages = {18079 -- 18086}, year = {2015}, abstract = {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.}, language = {en} } @article{UtechtPanKlamrothetal.2014, author = {Utecht, Manuel Martin and Pan, Tianluo and Klamroth, Tillmann and Palmer, Richard E.}, title = {Quantum chemical cluster models for chemi- and physisorption of chlorobenzene on Si(111)-7x7}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {118}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {33}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/jp504208d}, pages = {6699 -- 6704}, year = {2014}, abstract = {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.}, language = {en} } @article{KnieUtechtZhaoetal.2014, author = {Knie, Christopher and Utecht, Manuel Martin and Zhao, Fangli and Kulla, Hannes and Kovalenko, Sergey and Brouwer, Albert M. and Saalfrank, Peter and Hecht, Stefan and Bleger, David}, title = {ortho-Fluoroazobenzenes: visible light switches with very long-lived Z isomers}, series = {Chemistry - a European journal}, volume = {20}, journal = {Chemistry - a European journal}, number = {50}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201404649}, pages = {16492 -- 16501}, year = {2014}, abstract = {Improving the photochemical properties of molecular photoswitches is crucial for the development of light-responsive systems in materials and life sciences. ortho-Fluoroazobenzenes are a new class of rationally designed photochromic azo compounds with optimized properties, such as the ability to isomerize with visible light only, high photoconversions, and unprecedented robust bistable character. Introducing sigma-electron-withdrawing F atoms ortho to the N=N unit leads to both an effective separation of the n -> pi* bands of the E and Z isomers, thus offering the possibility of using these two transitions for selectively inducing E/Z iso-merizations, and greatly enhanced thermal stability of the Z isomers. Additional para-electron-withdrawing groups (EWGs) work in concert with ortho-F atoms, giving rise to enhanced separation of the n -> pi* transitions. A comprehensive study of the effect of substitution on the key photochemical properties of ortho-fluoroazobenzenes is reported herein. In particular, the position, number, and nature of the EWGs have been varied, and the visible light photoconversions, quantum yields of isomerization, and thermal stabilities have been measured and rationalized by DFT calculations.}, language = {en} } @article{HerderUtechtManickeetal.2013, author = {Herder, Martin and Utecht, Manuel Martin and Manicke, Nicole and Grubert, Lutz and P{\"a}tzel, Michael and Saalfrank, Peter and Hecht, Stefan}, title = {Switching with orthogonal stimuli electrochemical ring-closure and photochemical ring-opening of bis(thiazolyl) maleimides}, series = {Chemical science}, volume = {4}, journal = {Chemical science}, number = {3}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2041-6520}, doi = {10.1039/c2sc21681g}, pages = {1028 -- 1040}, year = {2013}, abstract = {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.}, language = {en} }