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 - 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 - 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 -