Considering isomerization of azobenzene and PSB4, we chose the following criterion to distinguish between the cis and trans photoproducts. If the dihedral angle falls within the range from -30 to 30 degrees between 175 and 200 fs, the product is of cis-structure. If the dihedral angle falls within the range of 150 to 210 degrees, the product is of trans-structure. Specifically, the dihedrals C3-N1-N2-C1 and C4-C5-C6-C7 were chosen for azobenzene and PSB4, respectively (cf. Ref. ).