Further, we computed quantum yields Φ for the trans→cis isomerization (see Table ). For the monomer, we find the quantum yield of about 15 %, in good agreement with the available literature values. For models with a = 5.5 Å, the quantum yield is reduced to Φ ≈ 5 %, for both free tetramer and SAM. Any of the four QM molecules can be switched for a = 5.5 Å. For tetramer 3.5 Å, Φ ≈ 4.6 %. In this case, for reactive trajectories, only end molecules (1 and 4) show isomerization. For SAM 3.5 Å no switching was observed, Φ = 0. We note that for the quantum yield calculations we used only those trajectories that reached the ground state (S 0 ) within 10 ps.