Nanocomposites and nanomaterials

Difference in refractive nonlinear optical response between Sudan dyes with single and double -N=N- bridges under pulsed laser excitation
Komarenko D.O. 1, Ovdenko V.M. 1,2, Multian V.V. 1, Gayvoronsky V.Ya.1
1 Advanced Materials Nonlinear Optical Diagnostics Lab, Institute of Physics of the NAS of Ukraine. pr. Nauki, 46, Kyiv 03028, Ukraine.                                                E-mail: vlad@iop.kiev.ua
2 Chemical Department, Taras Shevchenko National University of Kyiv, 60 Volodymyrska St., Kyiv 01033, Ukraine.       E-mail: valeryovdenko@gmail.com

Organic dye/polymer systems are a promising base for design of the multicomponent polymer composites and polymers with the covalently bonded photoactive chromophores. Linear and nonlinear optical properties of such materials depend on the electron donor/acceptor properties of substituent groups and their structural isomerism. Sudan colorants represent an important class of azo dyes having a developed delocalized π-electron system and high thermal stability.
We have studied self-action effects manifestation under picosecond range pulsed laser excitation in PMMA thin films with incorporated set of Sudan dyes having single (Sudan I and 1-(2-Pyridylazo)-2-naphthol) and double (Sudan IV and Sudan III) photoactive -N=N- π-bridges. We utilized the fundamental radiation (1064 nm) and its second harmonic (532 nm) of Nd:YAG laser corresponding to two types of the dyes molecules excitation: (1) resonant excitation of n-π transition with visible light [1]; and (2) two-photon excitation of the same band with IR radiation. 
Variation of azo groups amount in the molecule and donor substituent embedding into benzene ring provide switching between opposite signs of refractive nonlinear optical response (self-focusing vs self-defocusing effects). Addition of donor substituents in Sudan IV about five times increases self-focusing efficiency against Sudan III film at 1064 nm. In visible range the studied films demonstrated efficient self-focusing response with Re(χ(3) ~ (10-8 – 10-9 ) esu amid photobleaching effect up to 30% for Sudan IV film.

[1] Ovdenko V., Multian V., Uklein A., Kulai I., Kolendo A., Gayvoronsky V. Novel efficient nonlinear optical azo- and azomethine polymers containing antipyrine fragment: synthesis and characterization // J. Mater. Chem.  -2020.-№8.- P. 9032-9045