Ultrafastcis-transphotoswitching: A model study

Susanne Hahn, Gerhard Stock
2002 Journal of Chemical Physics  
A quantum-mechanical model description of a molecular photoswitch is developed. It takes into account ͑i͒ the electronic curve crossing arising from the cis-trans twisting of a double bond, resulting in an ultrafast internal-conversion process of the system and ͑ii͒ the coupling of the initially excited chromophore ͑the "system"͒ to the remaining degrees of freedom ͑the "bath"͒, affecting a vibrational cooling of the hot photoproducts. The latter mechanism is responsible for the localization of
more » ... the molecule in the cis and trans configuration, respectively, thus determining the quantum yield of the photoreaction. Following a discussion of the validity and the numerical implementation of the Redfield formulation employed, detailed numerical studies of the time-dependent dissipative photoisomerization dynamics are presented. While the short-time dynamics (Շ1 ps͒ is dominated by the coherent wave-packet motion of the system, the time evolution at larger times mainly reflects the interaction between system and bath. The quantum yield of the cis-trans forward reaction (Y c→t ) and the trans-cis backward reaction (Y t→c ) is shown to depend on the energy storage of the photoreaction and, in particular, on the form of the system-bath coupling. On the other hand, it is found that Y t→c ϭ1ϪY c→t , that is the population probabilities of the cis and trans configuration at long times do not depend on the initial preparation of the system.
doi:10.1063/1.1428344 fatcat:bgk22xiknnbbdksb7zooiol2de