To gain further insights into DESC, we studied various azoarene/PS combinations as noncovalent heterodimers using quantum chemical simulations. We consistently found that the lowest-energy triplet state (T1) within these heterodimers is localized on the PS and the second-lowest triplet state (T2) is localized on the azoarene, indicating that the PS→azoarene TET is an endothermic process (e.g., see Fig. for the energy diagram of 1⋅ps1). These results led us to hypothesize that the experimentally observed TET might be facilitated by thermal fluctuations of molecules, as suggested previously for other triplet donor-acceptor pairs . Therefore, we studied the variation of the 1⋅ps1 excited state energies on the C-N=N-C dihedral angle (Φ) in azobenzene 1 (which is significantly more flexible than ps1). Figure shows a relaxed scan for the 1⋅ps1 heterodimer, demonstrating that an 18º twist in Φ is sufficient to invert the energetic order of T1 and T2, making TET energetically favorable. We separately studied the dynamics of the (1⋅ps1)⊂C heterodimer by multiscale MD simulations (Supplementary Movie 1); these simulations reveal that thermal fluctuations readily allow 1 to adapt conformations with ΔΦ ≥ 18º at room temperature. 430 (absorbance at 430 nm immediately after photoexcitation) and ΔAbs ∞ 430 (steady-state absorbance). All the TAS results presented here were collected under ambient (non-deoxygenated) conditions. d, The energies of the S1, T1, and T2 states in the E-1⋅ps1 heterodimer (the T1 and T2 states are localized on ps1 and E-1, respectively). e, Ground-state relaxed scan along the C-N=N-C dihedral angle Φ in 1 within the 1⋅ps1 heterodimer. The black, red, and blue lines denote the ground state, the bright singlet state, and the two lowest triplet states, respectively. The green and gray markers correspond to the localization of the excited state on the donor (ps1) and acceptor (1), respectively. f, Ground-state relaxed scan of Φ in 1 within the (1⋅ps1)⊂C heterodimer (orange trace). The blue trace shows the energies corresponding to the same configurations of 1 and ps1 after removing the cage and its interactions. The scan was performed at the QM/QM2 hybrid scheme. g, Optimized geometries of (1⋅ps1)⊂C for the three ΔΦ values indicated in panel f (left: side views; right: top views). The distances between the indicated equatorial Pd nodes describe the degree of cage deformation; the larger the difference between the two Pd-Pd distances, the greater the transition of C from a tube-like conformation into a bowl-like conformation. The heterodimer structures (e-g) were optimized using B3LYP-D3/Def2-SVP, the excitation energies (d, e) were calculated at the SCS-ADC(2)//B3LYP-D3/Def2-SVP level of theory, and the cage and nitrate counterions (f, g) were treated using the semiempirical XTB1 method.