Light-induced deformation of side-chain azo-polyacrylate: Insights from atomistic modeling

Abstract

Fully atomistic molecular dynamics simulations are used to investigate light-induced deformation in amorphous side-chain azo-polyacrylates with flexible spacers. Illumination is modeled via an effective orientation potential acting on azobenzene chromophores, allowing nanosecond time scales to be accessed without explicit photoisomerization. Polarized light induces rapid reorientation of azobenzene units perpendicular to the polarization direction, followed by a much slower response of the polymer backbone. Above the glass transition temperature, this separation of time scales results in an initial contraction and subsequent uniaxial elongation of the sample along the light polarization, driven by backbone alignment rather than backbone stretching.Below the glass transition, chromophore reorientation leads only to contraction, while backbone conformations remain frozen. Chain length is found to have little influence on the observed behavior for the non-entangled systems studied. Analysis of spacer conformations and complementary quantum-chemical calculations show that the flexible alkyloxy-ester spacer accommodates light-induced torque primarily through torsional rearrangements, weakening and delaying torque transfer to the backbone.