Next‐generation quantum theory of atoms in molecules for the photochemical ring‐opening reactions of oxirane

Int J of Quantum Chemistry

et al. 2022

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We investigate the presence of helical character and chirality using a vector‐based charge density perspective instead of energetic or structural measures. The vector‐based perspective of the chemical bonding, constructed using the most preferred direction of charge density accumulation, finds the presence of induced symmetry‐breaking for α,ω‐disubstituted [4]cumulenes as the end groups are torsioned. The stress tensor trajectories Tσ(s) are used to provide the additional symmetry‐breaking required to quantify the degree and nature of the chirality and helical character. The S‐1,5‐dimethyl‐[4]cumulene contains a very low degree of chiral character but significant axiality(helicity) resulting in a weakly helical morphology of the corresponding Tσ(s). The (‐)S(‐), (+)S(‐) and (+)S(+) conformations of S‐1,5‐diamino‐[4]cumulene contain very significant degrees of both chirality and helical character resulting in helical morphology of the corresponding Tσ(s). We discuss the consequences for the Tσ(s) in locating chiral character in these molecules in future experiment investigations.

Section: Theory and Methodsmentioning

confidence: 99%

Chirality–helicity of cumulenes: A non‐scalar charge density derived perspective

Xing

Int J of Quantum Chemistry

et al. 2022

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“…The p and q are the 3-D paths that are constructed from the values of the least (e 1 ) and most (e 2 ) preferred directions of electronic charge density accumulation along the bond-path, referred to as r . For further discussions on the construction of bond-path framework set B{p ,q ,r } [31][32][33][34][35][36][37][38][39][40][41] , see the Supplementary Materials S2 .…”

Section: Theory and Methodsmentioning

confidence: 99%

Chirality-Helicity of Cumulenes: A Non-Scalar Charge Density Derived Perspective

Xing

et al. 2021

Preprint

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We investigate the presence of helical character and chirality using a vector-based charge density perspective instead of energetic or structural measures. The vector-based perspective of the chemical bonding, constructed using the most preferred direction of charge density accumulation, finds the presence of induced symmetry-breaking for α,ω-disubstituted [4]cumulenes as the end groups are torsioned. The stress tensor trajectories Tσ(s) are used to provide the additional symmetry-breaking required to quantify the degree and nature of the chirality and helical character. We find an absence of chirality for [4]cumulene but a very significant degree of axiality as demonstrated by the purely axial form of the Tσ(s) indicating a lack of helical character. The S-1,5-dimethyl-[4]cumulene contains a very low degree of chiral character but significant axiality(helicity) resulting in a weakly helical morphology of the corresponding Tσ(s). The (-)S(-), (+)S(-) and (+)S(+) conformations of S-1,5-diamino-[4]cumulene contain very significant degrees of both chirality and helical character resulting in helical morphology of the corresponding Tσ(s). The chirality assignments are in agreement with the Cahn–Ingold–Prelog (CIP) classifications for the (-)S(-), (+)S(-) and (+)S(+) conformations of S-1,5-diamino-[4]cumulene. We discuss the consequences for the Tσ(s) in locating chiral character in these molecules in future experiment investigations.

“…The QTAIM nonminimal 3D interpretation of the chemical bond used previously for excited state phenomena corresponds only to MEPs, and this work will be the first use of the bond‐path framework set B 0,1 to dynamics trajectories . In this investigation, we will present two selected dynamics trajectories fast ( F ) (hop time = 352 fs) and slow ( S ) (hop time = 574 fs) up to their respective CIs and analyze the directional BCP and bond‐path properties to gain insight into the different dynamics.…”

Section: Introductionmentioning

confidence: 99%

Next‐generation quantum theory of atoms in molecules for the S₁/S₀ conical intersections in dynamics trajectories of a light‐driven rotary molecular motor

Wang

Int J of Quantum Chemistry

et al. 2019

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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)