Ultrafast cis-trans photoswitching: A model study

摘要

A quantum-mechanical model description of a molecular photoswitch is developed. It take into account (i) 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 (ii) 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 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 dynamis (t)) and the trans-cis backward reaction (Y_(t-c)) isshown to depend on the energy storage of thephotoreaction and, in particular, on the form of hte system-bath coupling. On the other hand, it is found that Y_(t<-c)=1-Y_(c->t), that is the population probabilities of the cis and trans configuration at long times to not depend on the initial preparation of the system.