Influence of extrinsic and intrinsic parameters onto the formation of surface relief gratings in polar azo molecular glasses

Polar azo derivatives exhibiting stable glass-forming properties displayed efficient migration properties as thin films when subjected to interferential illumination, and formed time-stable and rewritable surface relief gratings as high as the initial film thickness. Intrinsic (film thickness, structure bulkiness) as well as extrinsic (laser fluence and polarization) parameters dramatically influenced the rate of the relief growth as well as the maximum relief amplitude. The superimposition of +45°/−45°-polarized beams unexpectedly conducted to a diffraction efficiency ten times as high as the combination of two p/p (parallel to the incident plane) polarized beams. The introduction of bulky anthryl Diels–Alder substituents showed net increase in the modulation amplitude due to the creation of large free volume around each azo unit, facilitating the azo migration within the less densely packed material.

► Surface relief gratings formed by illuminating polar azo molecular glasses are highly sensitive to free volume.
► Their modulation increases when the azo moieties are less densely packed.
► This was demonstrated through the introduction of bulky Diels–Alder substituents.
► Measurements provided low refractive indices in accord with a larger free volume induced around the migrating azo chromophores.