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.