The normal modes of vibration of benzene from the trajectories of stress tensor eigenvector projection space

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The realization of technologically relevant functional systems from idealized photochromic compounds remains elusive due to the double requirement that such switches must possess both highly efficient photo-isomerization reactivity and extremely low fatigue over a large number of switching cycles. Nowadays, improvements of the switching properties in complex diarylethene structures are mainly attained on a "trial and error" basis through chemical substitutions aimed at tuning the chemical properties of the core of the diarylethene. Therefore, we present new guiding principles to analyze the first excited state reactivity of diarylethenes based on the quantum theory of atoms in molecules (QTAIM) including the stress tensor. This approach straightforwardly provides consistent theoretical justification to partner the already successful symmetric substitution patterns obtained from experiments. The guiding principles provided by QTAIM and stress tensor suggest more complex asymmetric patterns should be included for the systematic design of new technologically relevant functional compounds. The stress tensor trajectory T r (s) analysis is used to characterize the photochromism reaction as reusable and the fatigue reaction as irreversible and find candidate sites for alteration by future experiment. K E Y W O R D S diarylethenes, photochromism, QTAIM, stress tensor

Section: Introductionmentioning

confidence: 99%

Fatigue and photochromism S₁ excited state reactivity of diarylethenes from QTAIM and the stress tensor

Yang

Momen

et al. 2017

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“…Consistency is found with our recent publication with the stress tensor trajectories and these four IR active normal modes; we again find that for mode 0014 and mode 0028 the CC BCPs excess BPL distortions indicate an equal or at least significant contribution to the normal mode of vibration. Conventional normal mode analysis determines that both modes only involve the CH bonds and again we find this is clearly an over simplification as is apparent for the nonzero variation in the BPL for the CC BCPs with amplitude, see Figure B,D, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…bond stretching/compression, without a significant degree of bond‐path torsion resulting from the zero bond‐path curvature throughout the duration of the normal mode. The nonzero variations in the bond‐path curvature of mode 0021 were apparent from the molecular graphs of the maximum ± amplitudes of the normal modes of vibration of our earlier work, therefore, we provide these plots for reference in the Supporting Information S8.…”

Section: Resultsmentioning

confidence: 99%

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A vector‐based representation of the chemical bond for the normal modes of benzene

Huang

Azizi

et al. 2018

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We introduce a vector-based interpretation of the chemical bond within the quantum theory of atoms in molecules (QTAIM), the bond-path framework set B = {p, q, r}, to follow variations in the 3D morphology of all bonds for the four infrared active normal modes of benzene. The bond-path framework set B comprises three unique paths p, q, and r where r is the familiar QTAIM bond concept of bond-path (r) while the two new paths p and q are formulated from the least and most preferred directions of electron density accumulation, respectively. We find 3D distortions including bond stretching/compression, torsion, and curving. We introduce two fractional measures to quantify these variations away from linearity of the bond.benzene, infrared spectroscopy, normal mode, quantum theory of atoms in molecules 1 | INTRODUCTION Two different approaches are used for the interpretation of vibrational spectroscopies using Raman Infrared (IR) [1][2][3] and inelastic incoherent neutron scattering of molecular structures. The first is the use of group theory with mathematical models of the forms and frequencies of the molecular vibrations including using normal mode coordinate analysis and symmetry assignments. The second is the use of empirical characteristic frequencies for chemical functional groups. We shall briefly illustrate the disadvantages of the first approach with the useful prototype of water ice, because it contains a mix of weak and strong bonding types. Previously, one of the current authors correlated the symmetry assignments of the zone-center normal modes of the proton ordered ice VIII and the corresponding frequencies with Raman, infrared, and incoherent neutron scattering spectra. [3] The comparison of the calculated frequencies with the Raman experiment spectra for the ice VIII O H sigma bonds for the symmetric and antisymmetric stretching modes was reasonable with only a 2% error for both of these modes. In calculations on this prototype system the errors were much larger for the bending, rotational and translational modes: up to 15%, 27%, and 10%, respectively. Contributions to the high frequency normal modes of vibration are dominated by the stronger O H sigma bonds conversely; the lower frequency modes are dominated by the vibrations of the weaker hydrogen bonds and O O bonding interactions. A reason for the much greater accuracy of the O H sigma

“…We propose to do this with the scalar and vector‐based aspects of the quantum theory of atoms in molecules (QTAIM) and the stress tensor formalism. In particular, we will use the QTAIM and stress tensor trajectory T σ ( s ) formalisms in the stress tensor trajectory space U σ to understand the functioning of the switch, previously used for benzene to present a new characterization of normal modes …”

Section: Introductionmentioning

confidence: 99%

Quinone‐based switches for candidate building blocks of molecular junctions with QTAIM and the stress tensor

Wang

Yang

et al. 2018

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The current work investigates candidate building blocks based on molecular junctions from hydrogen transfer tautomerization in the benzoquinone-like core of an azophenine molecule with QTAIM and the recently introduced stress tensor trajectory analysis. We find that in particular the stress tensor trajectories are well suited to describe the mechanism of the switching process. The effects of an Fe-dopant atom coordinated to the quinone ring, as well as F and Cl substitution of different ring-hydrogens, are investigated and the new QTAIM and stress tensor analysis is used to draw conclusions on the effectiveness of such molecules as molecular switches in nanosized electronic circuits. We find that the coordinated Fe-dopant greatly improves the switching properties, both in terms of the tautomerization barrier that has to be crossed in the switching process and the expected conductance behavior, while the effects of hydrogen substitution are more subtle. The absence of the Fe-dopant atom led to impaired functioning of the switch "OFF" mechanism as well as coinciding with the formation of closedshell H-H bond critical points that indicated a strained or electron deficient environment. Our analysis demonstrates promise for future use in design of molecular electronic devices. K E Y W O R D SQTAIM, quinone-based switche, stress tensor, stress tensor trajectory