Computational Details. All molecules were optimized with density functional theory (DFT) in the ground state electronic configuration, with-out influence of the cavity. Formaldehyde, 35PPE, and H 2 utilized the B3LYP/6-311++G** while aminopropenal was calculated with ωB97XD/6-311++G**. The excited states were calculated with time-dependent DFT (TD-DFT) at the same level of theory. All DFT, TD-DFT, and natural transition orbital (NTOs) calculations were performed using the Gaussian 16 software package. The dipole matrix elements, real-space projected transition densities, and transition density matrices were computed using the Multiwfn v3.7 software package. For formaldehyde and aminopropenal, Eq. 4 was solved with 500 electronic states and 10 Fock states. For 35PPE, Eq. 4 was solved with 100 electronic states and 10 Fock states The H 2 molecule was solved in the basis of 3 electronic states and 5 Fock states.