The efficient inscription of the surface relief gratings in novel polyimides with fluorine-substituted azobenzene

Combining polyimides, that exhibit heat resistivity with azo chromophores results in photosensitive materials with excellent properties for photonics and optoelectronics. The T-type structured polymer contain one or two azo chromophores per unit and different groups in polymer backbone. Due to photosensitivity of azo chromophores the molecules undergo trans-cis photomerization when the polymer is excited by light. This reaction enables the movement of material when the surface of the thin film sample is illuminated by two overlapping laser beams. As a result, surface relief grating (SRG) is created, and dynamic of its formation is studied by monitoring signal of diffraction. We will show that by proper choice of polymer backbone architecture it is possible to obtain grating depth of up to 300 nm, what corresponds to the diffraction efficiency of almost up to 18 % in the case of polymer with two azo chromophores per unit located between imide rings and amide groups. This is more than 7 times higher than the depth of SRG of the poorest performing polymer containing one azo group. Such results cannot be solely explained by the number of azo chromophores in the unit.