Next-generation quantum theory of atoms in molecules was applied to analyze, along an entire bond path, intramolecular interactions known to influence the photoisomerization dynamics of a light-driven rotary molecular motor. The 3D bondpath framework set B 0,1 constructed from the least and most preferred directions of electronic motion, provided new insights into the bonding leading to different S 1 state lifetimes including the first quantification of covalent character of a closed-shell intramolecular bond path. We undertook the first use of the stress tensor trajectory T σ (s) analysis on selected nonadiabatic molecular dynamics trajectories with the electron densities obtained using the ensemble density functional theory method.The stress tensor T σ (s) analysis was found to be well suited to follow the dynamics trajectories that included the S 0 and S 1 electronic states through the conical intersection and also provided to a new measure to assess the degree of purity of the axial bond rotation for the design of rotary molecular motors.light-driven molecular rotary motor, next-generation QTAIM, dynamics trajectories, conical intersection, stress tensor 1 | INTRODUCTION Previously, it was argued that replacing the torsion-pyramidalization conical intersections (CI) by chemical modification of the molecular skeleton would lead to molecular motors that would undergo pure axial rotation of its blades and thus possessing greater quantum efficiency than their overcrowded alkene analogues [1] ; these hypotheses later were confirmed by nonadiabatic molecular dynamics (NAMD) simulations. [2] These modified motors underwent pure axial rotations and the photochemical steps of the rotary motor cycle could access the S 1 /S 0 intersection very rapidly. This provided a purely chemical method for the control of the photoisomerization dynamics because previously this outcome was possible only for thermal relaxation of molecular motors.Previously, a quantum theory of atoms in molecules (QTAIM) [3] and stress tensor analysis were applied to analyze intramolecular interactions influencing the photoisomerization dynamics of a light-driven rotary molecular motor [4] obtained from the ensemble density functional theory method. The definition of the stress tensor is ambiguous due to the nature of the kinetic energy density. [5][6][7][8][9][10] The NAMD simulations of chemically modified molecular motors of the 3-[(2S)-2-fluoro-2-methyl-1-indanylidene]-1-methyl-2-methylindole (F-NAIBP) molecular rotary motor demonstrated the presence of fast (F) and slow (S) categories of dynamics trajectory [2] (Scheme S1 of Supplementary Materials S1). The fast (F) and slow (S)