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

Abstract

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

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

“…There is a strong contrast in the form of the trajectories T σ ( s ) of the H13–N10/N10H13 BCP and H13–N11/N11H13 BCP for the forward “OFF” switch position between the undoped and Fe‐doped quinone switches, see Figure A,B, respectively. The linear trajectories T σ ( s ) of the forward “OFF” switching in the undoped switch resembles the form of the trajectories T σ ( s ) for fatigue reaction recently examined, see Figure A whereas the validity of Hammond's postulate is again apparent for the Fe‐doped switch, see Figure B.…”

“…If the magnitude, that is, scalar length, of the BCP shift dr '( s ) and the direction of dr '( s ) are constant, then L σ = 0. Earlier, we used Equation to compare the values of the stress tensor trajectory length L σ between the photochromism and fatigue path‐ways BCP s of interest . The corresponding real space lengths l ( s ) of the T σ ( s ) are calculated as the sum: …”

Next‐generation QTAIM for scoring molecular wires in E‐fields for molecular electronic devices

“…[26] This directional approach can be used in a variety of circumstances where conventional QTAIM, [27] that only provides scalar measures such as bond ellipticity ε, is not useful. Examples that highlight the utility of this directional approach of next-generation QTAIM include understanding the consequences of application of external forces, for example, normal modes [26] excited states, torsions, [14,28,29] and stereochemistry. [30] Theory and methods…”

Fatigue and fatigue resistance in S1 excited state diarylethenes in electric fields

“…Earlier, some of the current authors considered the first excited state (S 1 ) reactivity of DTEs with developments of (QTAIM) [10] that we refer to as next generation QTAIM (NG‐QTAIM) [11] In the previous investigation of DTE, doped and sulfur doped, we mapped out the photochromism and fatigue mechanisms for the passage along internal reaction coordinate pathways in terms of the associated bonds (bond critical points) in a stress tensor space to gain insights into the characteristic behaviors. In particular, we found unfavorable fatigue switch characteristics such as discontinuous and nonreversible behaviors for the undoped DTE fatigue bond but not for the sulfur doped DTE switch fatigue bond.…”