Stimuli Thresholds for Isomerization-induced Molecular Motions in Azobenzene Containing Materials

TL;DR

This study uses molecular dynamics simulations to identify thresholds in azobenzene molecule isomerization that significantly enhance molecular mobility in host materials, confirming theoretical mechanisms.

Contribution

It demonstrates the existence of mobility thresholds related to isomerization amplitude, supporting the cage-breaking and gradient pressure mechanisms.

Findings

Mobility increases linearly with isomerization amplitude above thresholds.

Thresholds in diffusion are predicted by existing theories.

Simulation results confirm the role of shape modification in molecular motion.

Abstract

We use large scale molecular dynamics simulations of the isomerizations of azobenzene molecules diluted inside a simple molecular material, to investigate the effect of a modification of the cis isomer shape on the induced diffusion mechanism. To this end we simulate incomplete isomerizations, modifying the amplitude of the trans to cis isomerization. We find thresholds in the evolution of the host molecules mobility with the isomerization amplitude, a result predicted by the cage- breaking mechanism hypothesis (Teboul, V.; Saiddine, M.; Nunzi, J.M.; Accary, J.B. J. Chem. Phys. 2011, 134, 114517) and by the gradient pressure mechanism theory (Barrett, C.J.; Rochon, P.L.; Natansohn, A.L. J. Chem. Phys. 1998, 109, 1505-1516. ). Above the threshold the diffusion then increases linearly with the variation of the chromophore size induced by the isomerization.