Kinetics of photoinduced phase retardation in azo dye layer

ABSTRACT

Photoalignment of liquid crystals with azo dyes has a high potential for display and non-display applications. In this study, we report the existence of abnormal relaxation of photoinduced retardation in azo dye layers. Our results were obtained on the experimental setup, where the phase retardation of azo dye was measured by a photoelastic modulator. This phenomenon indicates that the role of the rotational diffusion coefficient must be carefully studied. Uniaxial Boltzmann–Smoluchowski model was used for theoretical analysis of the experimental results. With the model that includes the relative order parameter, we examined its kinetics during pumping and different relaxation processes. The proportionality between the photoinduced retardation and the relative order parameter has enabled us to study the kinetics of latter one under the hypothesis of temporal dependence of the rotational diffusion coefficient. A qualitative agreement between experimental measurements and model calculations adequately describes the photoinduced relaxation kinetics. The proposed methodology of computation of the relative order parameter is unbiased for all values of the material parameters.

GRAPHICAL ABSTRACT

KEYWORDS:

• Photoalignment
• azo dyes
• dark relaxation
• rotational diffusion model
• order parameter
• photoinduced anisotropy

Acknowledgements

This research was funded by the Russian Science Foundation, grant number 20-19-00201. Authors are also grateful for critical remarks to Prof. Victor Belyaev (Moscow Region State University).

Authorship contribution statement

V.C.: conceptualization, theory and formal analysis; V.K.: experiment; A.K.: theory, computations and manuscript preparation. The authors declare that they have no competing interest.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Russian Science Foundation [20-19-00201].