Enhanced photoswitching of bridged azobenzene studied by nonadiabatic ab initio simulation

Photoisomerization of a bridged azobenzene derivative (AB-C-2) is studied by nonadiabatic ab initio molecular dynamics simulation. The effect of the alkyl bridge linking the two phenyl rings on the Z -> E and E -> Z photoisomerization pathways and efficiencies is analyzed by detailed comparison to the unbridged parent compound. It is found that the bridge makes E -> Z photoisomerization considerably faster and increases its quantum yield, whereas Z -> E photoswitching is slightly hindered and has a significantly lower quantum yield although still being ultrafast. The simulations reveal that unsuccessful Z -> E photoisomerization attempts can interconvert two pro-enantiomeric forms of Z-AB-C-2 via pseudorotation in the excited electronic state. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733673]