TY - JOUR A1 - Wolf, Thomas J. A. A1 - Holzmeier, Fabian A1 - Wagner, Isabella A1 - Berrah, Nora A1 - Bostedt, Christoph A1 - Bozek, John A1 - Bucksbaum, Phil A1 - Coffee, Ryan A1 - Cryan, James A1 - Farrell, Joe A1 - Feifel, Raimund A1 - Martinez, Todd J. A1 - McFarland, Brian A1 - Mucke, Melanie A1 - Nandi, Saikat A1 - Tarantelli, Francesco A1 - Fischer, Ingo A1 - Gühr, Markus T1 - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra JF - Applied sciences N2 - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymines neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes. KW - ultrafast dynamics KW - Auger electron spectroscopy KW - photofragmentation KW - photochemistry Y1 - 2017 U6 - https://doi.org/10.3390/app7070681 SN - 2076-3417 VL - 7 IS - 7 PB - MDPI CY - Basel ER - TY - JOUR A1 - Weis, Philipp A1 - Hess, Andreas A1 - Kircher, Gunnar A1 - Huang, Shilin A1 - Auernhammer, Günter K. A1 - Koynov, Kaloian A1 - Butt, Hans-Jürgen A1 - Wu, Si T1 - Effects of Spacers on Photoinduced Reversible Solid-to-Liquid Transitions of Azobenzene-Containing Polymers JF - Chemistry - a European journal N2 - Photoisomerization in some azobenzene-containing polymers (azopolymers) results in reversible solid-to-liquid transitions because trans- and cis-azopolymers have different glass transition temperatures. This property enables photoinduced healing and processing of azopolymers with high spatiotemporal resolution. However, a general lack of knowledge about the influence of the polymer structure on photoinduced reversible solid-to-liquid transitions hinders the design of such novel polymers. Herein, the synthesis and photoresponsive behavior of new azopolymers with different lengths of spacers between the polymer backbone and the azobenzene group on the side chain are reported. Azopolymers with no and 20 methylene spacers did not show photoinduced solid-to-liquid transitions. Azopolymers with 6 or 12 methylene spacers showed photoinduced solid-to-liquid transitions. This study demonstrates that spacers are essential for azopolymers with photoinduced reversible solid-to-liquid transitions, and thus, gives an insight into how to design azopolymers for photoinduced healing and processing. KW - azobenzenes KW - isomerization KW - photochemistry KW - polymers KW - self-healing Y1 - 2019 U6 - https://doi.org/10.1002/chem.201902273 SN - 0947-6539 SN - 1521-3765 VL - 25 IS - 46 SP - 10946 EP - 10953 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Prüfert, Chris A1 - Urban, Raphael David A1 - Fischer, Tillmann Georg A1 - Villatoro, José Andrés A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Belder, Detlev A1 - Zeitler, Kirsten A1 - Löhmannsröben, Hans-Gerd T1 - In situ monitoring of photocatalyzed isomerization reactions on a microchip flow reactor by IR-MALDI ion mobility spectrometry JF - Analytical and bioanalytical chemistry : a merger of Fresenius' journal of analytical chemistry, Analusis and Quimica analitica N2 - The visible-light photocatalyticE/Zisomerization of olefins can be mediated by a wide spectrum of triplet sensitizers (photocatalysts). However, the search for the most efficient photocatalysts through screenings in photo batch reactors is material and time consuming. Capillary and microchip flow reactors can accelerate this screening process. Combined with a fast analytical technique for isomer differentiation, these reactors can enable high-throughput analyses. Ion mobility (IM) spectrometry is a cost-effective technique that allows simple isomer separation and detection on the millisecond timescale. This work introduces a hyphenation method consisting of a microchip reactor and an infrared matrix-assisted laser desorption ionization (IR-MALDI) ion mobility spectrometer that has the potential for high-throughput analysis. The photocatalyzedE/Zisomerization of ethyl-3-(pyridine-3-yl)but-2-enoate (E-1) as a model substrate was chosen to demonstrate the capability of this device. Classic organic triplet sensitizers as well as Ru-, Ir-, and Cu-based complexes were tested as catalysts. The ionization efficiency of theZ-isomer is much higher at atmospheric pressure which is due to a higher proton affinity. In order to suppress proton transfer reactions by limiting the number of collisions, an IM spectrometer working at reduced pressure (max. 100 mbar) was employed. This design reduced charge transfer reactions and allowed the quantitative determination of the reaction yield in real time. Among 14 catalysts tested, four catalysts could be determined as efficient sensitizers for theE/Zisomerization of ethyl cinnamate derivativeE-1. Conversion rates of up to 80% were achieved in irradiation time sequences of 10 up to 180 s. With respect to current studies found in the literature, this reduces the acquisition times from several hours to only a few minutes per scan. KW - microchip KW - reaction monitoring KW - IR-MALDI KW - ion mobility spectrometry KW - photochemistry KW - photocatalysis KW - Olefin isomerization Y1 - 2020 U6 - https://doi.org/10.1007/s00216-020-02923-y SN - 1618-2642 SN - 1618-2650 VL - 412 IS - 28 SP - 7899 EP - 7911 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Matic, Aleksandar A1 - Schlaad, Helmut T1 - Thiol-ene photofunctionalization of 1,4-polymyrcene JF - Polymer international N2 - 1,4-Polymyrcene was synthesized by anionic polymerization of -myrcene and was subjected to photochemical functionalization with various thiols (i.e. methyl thioglycolate, methyl 3-mercaptopropionate, butyl 3-mercaptopropionate, ethyl 2-mercaptopropionate and 2-methyl-2-propanethiol) using benzophenone/UV light as the radical source. The yield of thiol addition to the trisubstituted double bonds of 1,4-polymyrcene decreased in the order 1 degrees thiol (ca 95%) > 2 degrees thiol (ca 80%) > 3 degrees thiol (<5%), due to the reversibility of the thiol-ene reaction. Remarkably, thiol addition to the side-chain double bonds was 8 - 10 times (1 degrees thiol) or 24 times (2 degrees thiol) faster than to the main-chain double bonds, which can be explained by the different accessibility of the double bonds and steric hindrance. Despite the use of a 10-fold excess of thiol with respect to myrcene units, the thiol-ene addition was accompanied by chain coupling reactions, which in the extreme case of 3 degrees thiol (or in the absence of thiol) resulted in the formation of insoluble crosslinked material. As an example, a methyl-thioglycolate-functionalized 1,4-polymyrcene was saponified/crosslinked to give submicron polyelectrolyte particles in dilute alkaline solution. (c) 2018 Society of Chemical Industry KW - polymyrcene KW - thiol-ene KW - photochemistry KW - regioselectivity Y1 - 2018 U6 - https://doi.org/10.1002/pi.5534 SN - 0959-8103 SN - 1097-0126 VL - 67 IS - 5 SP - 500 EP - 505 PB - Wiley CY - Hoboken 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 - Hardy, John G. A1 - Bertin, Annabelle A1 - Torres-Rendon, Jose Guillermo A1 - Leal-Egana, Aldo A1 - Humenik, Martin A1 - Bauer, Felix A1 - Walther, Andreas A1 - Cölfen, Helmut A1 - Schlaad, Helmut A1 - Scheibel, Thomas R. T1 - Facile photochemical modification of silk protein-based biomaterials JF - Macromolecular bioscience N2 - Silk protein-based materials show promise for application as biomaterials for tissue engineering. The simple and rapid photochemical modification of silk protein-based materials composed of either Bombyx mori silkworm silk or engineered spider silk proteins (eADF4(C16)) is reported. Radicals formed on the silk-based materials initiate the polymerization of monomers (acrylic acid, methacrylic acid, or allylamine) which functionalize the surface of the silk materials with poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(allylamine) (PAAm). To demonstrate potential applications of this type of modification, the polymer-modified silks are mineralized. The PAA- and PMAA-functionalized silks are mineralized with calcium carbonate, whereas the PAAm-functionalized silks are mineralized with silica, both of which provide a coating on the materials that may be useful for bone tissue engineering, which will be the subject of future investigations. KW - biomaterials KW - chemical modification KW - photochemistry KW - silkworm silk KW - spider silk Y1 - 2018 U6 - https://doi.org/10.1002/mabi.201800216 SN - 1616-5187 SN - 1616-5195 VL - 18 IS - 11 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Goebel, Ronald A1 - Hesemann, Peter A1 - Friedrich, Alwin A1 - Rothe, Regina A1 - Schlaad, Helmut A1 - Taubert, Andreas T1 - Modular thiol-ene chemistry approach towards mesoporous silica monoliths with organically modified pore walls JF - Chemistry - a European journal N2 - The surface modification of mesoporous silica monoliths through thiol-ene chemistry is reported. First, mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol-gel hydrolysis-poly-condensation reaction from tetramethyl orthosilicate (TMOS) and vinyltriethoxysilane, allyltriethoxysilane, and (3-mercaptopropyl) trimethoxysilane, respectively. By variation of the molar ratio of the comonomers TMOS and functional silane, mesoporous silica objects containing different amounts of vinyl, allyl, and thiol groups were obtained. These intermediates can subsequently be derivatized through radical photoaddition reactions either with a thiol or an olefin, depending on the initial pore wall functionality, to yield silica monoliths with different pore-wall chemistries. Nitrogen sorption, small-angle X-ray scattering, solid-state NMR spectroscopy, elemental analysis, thermogravimetric analysis, and redox titration demonstrate that the synthetic pathway influences the morphology and pore characteristics of the resulting monoliths and also plays a significant role in the efficiency of functionalization. Moreover, the different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore-wall functionalization. This report demonstrates that thiol-ene photoaddition reactions are a versatile platform for the generation of a large variety of organically modified silica monoliths with different pore surfaces. KW - mesoporous materials KW - photochemistry KW - sol-gel processes KW - surface chemistry Y1 - 2014 U6 - https://doi.org/10.1002/chem.201403982 SN - 0947-6539 SN - 1521-3765 VL - 20 IS - 52 SP - 17579 EP - 17589 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Füchsel, Gernot A1 - Tremblay, Jean Christophe A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Selective excitation of molecule-surface vibrations in H2 and D2 dissociatively adsorbed on Ru(0001) JF - Israel journal of chemistry N2 - In this contribution we report about the selective vibrational excitation of H2 and D2 on Ru(0001) as an example for nonadiabatic coupling of an open quantum system to a dissipative environment. We investigate the possibility of achieving state-selective vibrational excitations of H2 and D2 adsorbed on a Ru(0001) surface using picosecond infrared laser pulses. The systems behavior is explored using pulses that are rationally designed and others that are optimized using a time-local variant of Optimal Control Theory. The effects of dissipation on the laser-driven dynamics are studied using the reduced-density matrix formalism. The non-adiabatic couplings between adsorbate and surface are computed perturbatively, for which our recently introduced state-resolved anharmonic rate model is used. It is shown that mode- and state-selective excitation can be achieved in the absence of dissipation when using optimized laser pulses. The inclusion of dissipation in the model reduces the state selectivity and the population transfer yield to highly excited states. In this case, mode activation is most effectively realized by a rational pulse of carefully chosen duration rather than by a locally optimized pulse. KW - dissipative dynamics KW - photochemistry KW - quantum control KW - surface chemistry Y1 - 2012 U6 - https://doi.org/10.1002/ijch.201100097 SN - 0021-2148 VL - 52 IS - 5 SP - 438 EP - 451 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Fudickar, Werner A1 - Bauch, Marcel A1 - Ihmels, Heiko A1 - Linker, Torsten T1 - DNA-triggered enhancement of singlet oxygen production by pyridinium alkynylanthracenes JF - Chemistry - a European journal N2 - There is an ongoing interest in O-1(2) sensitizers, whose activity is selectively controlled by their interaction with DNA. To this end, we synthesized three isomeric pyridinium alkynylanthracenes 2 o-p and a water-soluble trapping reagent for O-1(2). In water and in the absence of DNA, these dyes show a poor efficiency to sensitize the photooxygenation of the trapping reagent as they decompose due to electron transfer processes. In contrast, in the presence of DNA O-1(2) is generated from the excited DNA-bound ligand. The interactions of 2 o-p with DNA were investigated by thermal DNA melting studies, UV/vis and fluorescence spectroscopy, and linear and circular dichroism spectroscopy. Our studies revealed an intercalative binding with an orientation of the long pyridyl-alkynyl axis parallel to the main axis of the DNA base pairs. In the presence of poly(dA : dT), all three isomers show an enhanced formation of singlet oxygen, as indicated by the reaction of the latter with the trapping reagent. With green light irradiation of isomer 2 o in poly(dA : dT), the conversion rate of the trapping reagent is enhanced by a factor >10. The formation of O-1(2) was confirmed by control experiments under anaerobic conditions, in deuterated solvents, or by addition of O-1(2) quenchers. When bound to poly(dG : dC), the opposite effect was observed only for isomers 2 o and 2 m, namely the trapping reagent reacted significantly slower. Overall, we showed that pyridinium alkynylanthracenes are very useful intercalators, that exhibit an enhanced photochemical O-1(2) generation in the DNA-bound state. KW - Anthracene KW - DNA KW - intercalations KW - photochemistry KW - singlet oxygen Y1 - 2021 U6 - https://doi.org/10.1002/chem.202101918 SN - 1521-3765 VL - 27 IS - 54 SP - 13591 EP - 13604 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Floss, Gereon A1 - Granucci, Giovanni A1 - Saalfrank, Peter T1 - Surface hopping dynamics of direct trans -> cis photoswitching of an azobenzene derivative in constrained adsorbate geometries JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - With ongoing miniaturization of electronic devices, the need for individually addressable, switchable molecules arises. An example are azobenzenes on surfaces which have been shown to be switchable between trans and cis forms. Here, we examine the "direct" (rather than substrate-mediated) channel of the trans -> cis photoisomerization after pi pi* excitation of tetra-tert-butyl-azobenzene physisorbed on surfaces mimicking Au(111) and Bi(111), respectively. In spirit of the direct channel, the electronic structure of the surface is neglected, the latter merely acting as a rigid platform which weakly interacts with the molecule via Van-der-Waals forces. Starting from thermal ensembles which represent the trans-form, sudden excitations promote the molecules to pi pi*-excited states which are non-adiabatically coupled among themselves and to a n pi*-excited and the ground state, respectively. After excitation, relaxation to the ground state by internal conversion takes place, possibly accompanied by isomerization. The process is described here by "on the fly" semiclassical surface hopping dynamics in conjunction with a semiempirical Hamiltonian (AM1) and configuration-interaction type methods. It is found that steric constraints imposed by the substrate lead to reduced but non-vanishing, trans -> cis reaction yields and longer internal conversion times than for the isolated molecule. Implications for recent experiments for azobenzenes on surfaces are discussed. KW - AM1 calculations KW - bismuth KW - configuration interactions KW - excited states KW - gold KW - isomerisation KW - organic compounds KW - photochemistry KW - van der Waals forces Y1 - 2012 U6 - https://doi.org/10.1063/1.4769087 SN - 0021-9606 VL - 137 IS - 23 PB - American Institute of Physics CY - Melville ER -