Photo-Switching dynamics of azo-phenylcarbazoles in polycarbonate around β transition temperature

Second order non-linear optical features of azophenylcarbazole based derivative 9-(2,3-epoxy)propyl-2-(2,3-epoxy)propoxy-3-(4-nitrophenyl)azo-9H-carbazole in polycarbonate investigated at temperature 240 K, which is close to β transition for polycarbonate, are presented. Using all-optical poling technique writing and reading kinetics of second order susceptibility gratings in the azophenylcarbazole derivative were measured. Theoretical modelling of the experimental results indicates two cis-trans thermoisomerization rates in the range of k₁ = (2.5-3.3)×10^-3 s^-1, k₂ = (6.3-7.14)×10^-4 s^-1 depending on writing laser beam intensities (I_ω= 0.75-1.43 J/cm², I_2ω= 0.5-0.96 mJ/cm²); with slightly lower rates for the lower writing beam fluence. The orientational diffusion rate 1.43·10^-5 s^-1 does not depend on the writing conditions. The result indicates that the range of writing conditions used has very minor or even no influence over the intermolecular interaction observed during the all-optical poling process.