Freezing out all-optical poling dynamics of azophenylcarbazole molecules in polycarbonate

Abstract

In this work we have extended the application of a theoretical model describing the processes of all-optical poling of isomerizable molecules while taking into consideration the thermoisomerization related findings presented in the literature. A model describing all-optical poling transients using a three relaxation rate approach was contrasted with the experimental results of azophenylcarbazole doped polycarbonate measured in a wide range of temperatures from 150 to 300 K, thus covering the β transition for the host. By means of a long timescale and low temperature, we were able to better resolve the thermoisomerization and orientational diffusion processes. The cis→trans thermoisomerization relaxation rates k1 and k2 were obtained in the range 10(-5) to 10(-2) s(-1) and the relaxation rate k3 of the orientational diffusion of the trans isomer in the range 10(-6) to 10(-4) s(-1). The rates exhibited diverse temperature dependent behaviors: the two lowest (k2,k3) manifested Arrhenius type dependencies (Ek2 = 157 meV), whereas, the highest (k1) showed a temperature dependence that is non-Arrhenius, or undistinguished for our experimental conditions. The latter was interpreted using the geometrical "adjustment" model. By investigating chromophore-polymer systems at temperatures far below Tg, we were able to uncover the situation when the cis→trans transition is switched-off and the orientational randomization is suppressed. Thus, we could consider the chromophores as "frozen".

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

“…Fig. 2) according to equation (1) in [7]. I ω = 0.75 J/cm 2 I 2ω = 0.5 mJ/cm 2 9 2.5×10 -3 6.3×10 -4 Regardless the writing conditions, poling proceeds in a quite similar way and reaches saturation after ~10 min for both temperatures.…”

“…The time domain during which much slower decay rates are observed mainly corresponds to the loss of induced polar order by thermally induced orientational diffusion. A theoretical model was developed to fit the experimental results for azophenylcarbazole doped polycarbonate [7]. The best fit simulations of the decay transients validated that the thermal cis-trans isomerization process comprises a composition of two different isomerization reaction rates: a fixed relaxation rate k 1 corresponding to a lifetime of τ c1 = 300 s, which does not show any dependence on temperature, and a temperature dependent relaxation rate k 2 .…”

“…Investigation of optical poling transients as a function of azo-dye donor embranchment has demonstrated relatively higher poling efficiencies for larger molecules. By means of experiment and simulation we have shown how temperature reduces the cis-trans reverse isomerization and reorientation of the chromophores using the example of two azophenylcarbazole samples consisting of different donor arrangements [7]. In this work, we present and analyse the all-optical poling kinetics of an azophenylcarbazole based derivative as a function of intensity of the second order nonlinear susceptibility grating writing beams at low temperatures, far below T g .…”

From cis-Lobeline to trans-Lobeline: Study on the Pharmacodynamics and Isomerization Factors

“…However, as described in the introduction section, thermoisomerization is one of the types of transformation of cis-trans isomers. Isomerization due to temperature changes is a very common phenomenon [ 22 , 23 ]. As shown in Figure 3 , after being treated by different temperatures, there are significant differences in the excitatory effects of lobeline solutions with different degrees of isomerization on respiration.…”