The SAM 5.5 Å model is shown in Fig. . All other studied models may be obtained from this model by changing lattice parameters and, in the case of the free tetramers, by removing the perimeter molecules. The lattice parameters are a = 5.50 Å and b = 9.43 Å for SAM 5.5 Å, and a = 3.50 Å and b = 6.00 Å for SAM 3.5 Å (the a/b ratio is the same in both cases, a/b ≈ 0.583). The SAM models are described using a quantum mechanics/molecular mechanics (QM/MM) approach: the central tetramer (thick molecules in Fig. ) is the QM part and the perimeter (thin) molecules form the MM part. Further visualizations of the studied systems are provided in ref. 47 (see Fig. and Fig. there). We also note that these models represent an extension of our earlier models based on a QM dimer. To model nonadiabatic dynamics induced by visible light (nπ * ) excitation we use the approach applied in ref. 47 to study relaxation after UV (ππ * ) excitation. In this approach, the electronic structure of the QM tetramer is modeled with configuration interaction singles (CIS) based on molecular orbitals (MO) obtained from a self-consistent field calculation with floating occupation (FO) numbers 59 using the Austin Model 1 (AM1) that was reparameterized (r) for azobenzene. The method is abbreviated as rAM1/FOMO-CIS in what follows. For the CIS calculations, a restricted active space of eight highest occupied (HO) and four lowest unoccupied (LU) (also referred to as virtual) MOs was used. This active space includes orbitals originating from HOMO-1 (π), HOMO (n), and LUMO (π * ) of a monomer (the orbitals are shown in Fig. of ref. 47). In total, 65 Slater determinants are used to construct electronic wave functions.