Next, for the reactive trajectories, it is interesting to analyze which monomer undergoes isomerization. We note that, for the reactive trajectories, usually only one of the four monomers switches to the cis form (only three trajectories exhibit additional isomerizations caused by repopulation of excited states from the ground state). For tetramer 3.5 Å, out of 11 reactive trajectories, we find that 4, 1, 0, and 6 correspond to isomerization of monomers 1, 2, 3, and 4, respectively (see Fig. for numbering of the monomers). Thus, for tetramer 3.5 Å there is a preference for isomerization of end molecules (1 and 4). For tetramer 5.5 Å, out of 12 reactive trajectories, 3, 3, 3, and 3 show isomerization of monomers 1, 2, 3, and 4, respectively. In this case, we find a uniform "distribution". However, the overall quantum yields of tetramers 3.5 and 5.5 Å are very similar (both ∼8%). Thus, despite the fact that every QM molecule can isomerize in tetramer 5.5 Å, it turns out that azobenzene isomerization ability is affected at a = 5.5 Å. For SAM 5.5 Å, out of 10 reactive trajectories, we find 4, 3, 2, and 1 trajectories with switching of monomer 1, 2, 3, and 4, respectively. In this case the "distribution" is asymmetric which can originate from too few members of the sample.