Are azobenzenophanes rotation-restricted?

We simulated the photoisomerization dynamics of an azobenzenophane with a semiclassical surface hopping approach and a semiempirical reparametrized quantum mechanics/molecular mechanics Hamiltonian. Only one of the two azobenzene chromophores in the molecule is taken into account quantum mechanically: the other one is treated by molecular mechanics. Both n ->pi* and pi excitations are considered. Our results show that the photoisomerization reaction mainly involves the rotation around the N=N double bond. The excited state relaxation features are in qualitative agreement with experimental time-resolved fluorescence results. (c) 2005 American Institute of Physics.