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  - 
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  -