In this work, using first-principles calculations, we study how conformational disorder caused by nuclear motion affects the exciton states of a model azobenzene aggregate composed of four molecules (Fig. ). To this aim, we (i) perform ground-state Born-Oppenheimer molecular dynamics (BOMD) simulations employing dispersion-corrected density functional theory (DFT), (ii) calculate electronic spectra for selected MD snapshots using linear response, long-range corrected time-dependent DFT (TD-DFT), and (iii) reveal the nature of the exciton states by means of a transition density matrix (TDM) analysis. Specifically, in step (i) we perform B3LYP +D3(BJ) constant-temperature, groundstate dynamics at ∼300 K, † for 10 ps. After that, 100 snapshots are selected from the BOMD trajectory (with a time interval of 100 fs) and subjected to TD-DFT calculations using the ωB97X-D functional 22 (step ii). We use a long-range corrected functional in TD-DFT calculations to avoid a spurious charge transfer problem, which has been observed for azobenzene dimers when using standard hybrid functionals like B3LYP. All calculations are performed with the def2-SV(P) basis set 26 using Gaussian 16. Further details about the model and the methods are provided in SI1. † In general, for a nonlinear polyatomic molecule with N atoms, temperature is related to the kinetic energy as E kin = (3N -6) 2 kT . However, in our models the four lowest hydrogen atoms are fixed, and thus E kin = (3N -12 -1) 2 k T (here, 12 corresponds to frozen coordinates of four fixed atoms and 1 accounts for the rigid-body rotation around the axis going through the fixed atoms). Therefore, T = 3N -6 3N -13 T , which results in T ≈ 307.6 K for T = 300 K (N = 96).