Kinetic Monte Carlo simulations for birefringence relaxation of photo-switchable molecules on a surface

Tavarone, Raffaele; Stark, Holger

doi:10.1063/1.4943393

Cited by 6 publications

(13 citation statements)

References 67 publications

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“…They found that the dynamics slows down or accelerates depending on the probe's roughness, while the DHs increase in both cases, and concluded that probes can promote dynamic heterogeneities. In 2009, we found that dynamical defects created by probes isomerizing inside the medium can strongly promote DHs [16,17] while accelerating the dynamics, results that were confirmed by experiments and simulations [18][19][20][21][22]. Following these works, results on colloids [23][24][25][26][27], and theoretical findings [28][29][30], in order to test the hypothesis of a packing fluctuation origin of the DHs, we investigate in this paper the effect of small structural defects on the dynamics of a model supercooled liquid and on the strength of dynamic heterogeneity.…”

Section: Introductionmentioning

confidence: 53%

How do packing defects modify the cooperative motions in supercooled liquids?

et al. 2017

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We use molecular dynamic simulations to investigate the relation between the presence of packing defects in a glass-former and the spontaneous cooperative motions called dynamic heterogeneity. For that purpose we use a simple diatomic glass-former and add a small number of larger or smaller diatomic probes. The diluted probes modify locally the packing, inducing structural defects in the liquid, while we find that the number of defects is small enough not to disturb the average structure. We find that a small packing modification around a few molecules can deeply influence the dynamics of the whole liquid, when supercooled. When we use small probe molecules, the dynamics accelerates and the dynamic heterogeneity decreases. In contrast, for large probes the dynamics slows down and the dynamic heterogeneity increases. The induced heterogeneities and transport coefficient modification increase when the temperature decreases and disappear around the onset temperature of the cage dynamics.

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Section: Introductionmentioning

confidence: 53%

How do packing defects modify the cooperative motions in supercooled liquids?

et al. 2017

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“…There are relatively few simulations of photoresponse within a polymer or molecular glass. Recent exceptions have used lattice-based Monte-Carlo approaches to model glasses or tethered molecules . This gap is largely due to the difficulty of simultaneously modeling a large number of high-molecular weight molecules and the quantum-mechanical photoactivation process.…”

Section: Introductionmentioning

confidence: 99%

Vapor-Deposited Glasses Highlight the Role of Density in Photostability

et al. 2020

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Photoresponsive molecules can be integrated into glassy materials to probe the local environment and invoke responsive changes in polymer behavior. For example, recent experiments and simulations have studied increased stability in vapor-deposited glasses by examining the photoisomerization rate of a probe molecule. At the theoretical level, past work relied on coarse-grained simulations to explain the role of photoisomerization on glass behavior. In order to effectively exploit these molecular probes, an ability to quantify how the local environment influences the photoisomerization rate is needed. In this work, we present all-atom molecular-dynamics (MD) simulations of molecular glasses of photoresponsive azobenzene (AB) molecules. The stability of these in-silico samples is probed using photoisomerization, where AB molecules can undergo trans → cis transition upon light exposure. Vapor-deposited and bulk-cooled glasses of AB are simulated using a classical dihedral-switching potential developed by Bockmann et al. (J. Phys. Chem. A 2010, 114, 745−754) to model the photoisomerization process. The MD simulations include thousands of molecules and run for tens of nanoseconds. These size and time scales allow us to explore the broad distribution of photoisomerization wait times, which yields two results. First, the wait-time distributions for both physical vapor deposition and bulk-cooled glasses depend strongly on sample and local density, showing that density or local packing is a primary factor in glass stability against photoisomerization and the experimentally measured photoresponse. Second, the distribution follows a power-law with exponent b ≈ 1.25−1.3 that extends to longer times with increasing density. The power-law distribution suggests a connection with previous experiments that related barriers to photoisomerization with an effective photoisomerization temperature.

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“…Indeed, characteristics of the glass-transition physics like cooperative motions called dynamic heterogeneities were reported to be generated during the motion of various motors [38][39][40][41][42]. The photo-fluidization and softening of the host material, or transient liquid-like behaviors, were also reported by different groups experimentally and by simulations [38,[43][44][45][46] with particular motors.…”

Section: Introductionmentioning

confidence: 89%

“…Inside supercooled liquids and soft matter their motion is even more interesting as a source of information on the still unsolved physics of the glass-transition [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Indeed, characteristics of the glass-transition physics like cooperative motions called dynamic heterogeneities were reported to be generated during the motion of various motors [38][39][40][41][42]. The photo-fluidization and softening of the host material, or transient liquid-like behaviors, were also reported by different groups experimentally and by simulations [38,[43][44][45][46] with particular motors.…”

Section: Introductionmentioning

confidence: 99%

Folding time dependence of the motions of a molecular motor in an amorphous medium

et al. 2017

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We investigate the dependence of the displacements of a molecular motor embedded inside a glassy material on its folding characteristic time τ f . We observe two different time regimes. For slow foldings (regime I) the diffusion evolves very slowly with τ f , while for rapid foldings (regime II) the diffusion increases strongly with τ f ( D ≈ τ −2 f ) suggesting two different physical mechanisms. We find that in regime I the motor's displacement during the folding process is counteracted by a reverse displacement during the unfolding, while in regime II this counteraction is much weaker. We notice that regime I behavior is reminiscent of the scallop theorem that holds for larger motors in a continuous medium. We find that the difference in the efficiency of the motor's motion explains most of the observed difference between the two regimes. For fast foldings the motor trajectories differ significantly from the opposite trajectories induced by the following unfolding process, resulting in a more efficient global motion than for slow foldings. This result agrees with the fluctuation theorems expectation for time reversal mechanisms. In agreement with the fluctuation theorems we find that the motors are unexpectedly more efficient when they are generating more entropy, a result that can be used to increase dramatically the motor's motion.

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Kinetic Monte Carlo simulations for birefringence relaxation of photo-switchable molecules on a surface

Cited by 6 publications

References 67 publications

How do packing defects modify the cooperative motions in supercooled liquids?

How do packing defects modify the cooperative motions in supercooled liquids?

Vapor-Deposited Glasses Highlight the Role of Density in Photostability

Folding time dependence of the motions of a molecular motor in an amorphous medium

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