The effect of dye-polymer interactions on the kinetics of the isomerization of 4-dimethylaminoazobenzene and mercury dithizonate

Abstract

Neste trabalho as isomerizações térmica e fotoquímica do 4-dimetilaminoazobenzeno e do ditizonato de mercúrio foram estudadas tanto em solventes quanto em matrizes poliméricas. A cinética destas reações foi estudada usando-se funções exponenciais para o cálculo das constantes aparentes de velocidade. Observou-se que o comportamento cinético em soluções pode ser descrito por uma função mono-exponencial, enquanto que em sistemas poliméricos têm-se que empregar funções bi-exponenciais. As constantes de velocidades são fortemente influenciadas pelas interações soluto/solvente (ou polímero) além de, também, serem influenciadas pelos processos de tratamento térmico dos filmes poliméricos. Observou-se que, em geral, as reações são mais rápidas em meios mais polares (solventes e polímeros) devido a estabilização de diferentes tautômeros.Thermal and photo-isomerization reactions of mercury dithizonate and 4-dimethylaminoazobenzene were studied in solutions and in polymer matrices. We used exponential functions to calculate the rate constants for both processes. The kinetic behavior was well described by monoexponential functions for these dyes dissolved in solvents, although bi-exponential functions are required when these dyes are dissolved in polymers. The rate constants are strongly influenced by dye/solvent and dye/polymer interactions, as well as by the aging processes of the polymer matrix. In general, the reaction is faster in more polar mediums, solvents or polymer matrices, since stabilization of different tautomers takes place. We also showed that larger molecules isomerize slowly and slower isomerization has also been observed for annealed samples. Both results are attributed to the importance of free-volumes in polymeric matrices.Keywords: 4-dimethylaminoazobenzene, mercury dithizonate, polystyrene, poly(methyl methacrylate), thermoisomerization IntroductionAzo-dyes are one of the most important and versatile classes of synthetic organic compounds, with an enormous variety of applications. [1][2][3][4] Technological applications of these dyes result from the combination of the properties of the azo-group and several types of aromatic-substituted ligands that confer to them intense color over the whole visible range, thermal and photochemical stability, noncomplex synthetic methodologies and low costs of production. More recently, some of these dyes have been studied as materials for non-linear optical applications when they contain substituents on the aromatic rings with push-pull electron ability. 1,2,5,6 This confers to the dye a very large permanent electrical dipole moment improving the non-linear optical properties. Non-linear optical properties of several types of azodyes make them very useful for photonic devices, surface gratings, [8][9][10][11][12] photo-alignment in liquid crystalline polymers, 13 storage information among other applications.14 One requirement for second order non-linear susceptibility is to produce materials without centrosymmetry order of the dye arrangement.7 Thus, to avoid the p...

Responsive behavior of 4-(N-maleimido)azobenzene in polymers with aromatic main chain and side chain linked units

“…The insoluble maleamic acid was separated by filtration, washed with acetone and then added to a solution of sodium acetate in acetic anhydride (30 mL, 0.025 mol) in order to cyclize to the corresponding maleimide. The reaction was conducted under nitrogen at 80 o C for 4 h. The mixture was poured into a saturated aqueous solution of NaHCO 3 …”

“…Their potential use in optics or optoelectronics, such as for information storage, optical switching devices, surface relief gratings, nonlinear optics, etc has been motive the attention of the researchers and end users. [1][2][3][4][5][6][7][8][9][10] Large area of applications of azobenzene compounds is possible due to both its photoinduced properties and wide variety of the systems that it contained. Azobenzene chromophore has unique optical and photochemical properties.…”

“…Several approaches were used to insert azobenzene chromophores into polymer matrices: randomly incorporation (guest-host structures), binding to main or side chains, or formation of thin-layer structures like Langmuir-Blodgett films. [2][3][4][5][13][14][15] Azobenzene-containing polymers have been investigated with regard to different phenomena associated with the photochromic nature of the azobenzene moiety. Their conformational modifications induced by photo-or thermal isomerization of the azobenzene chromophore give the possibility to control some physical and chemical properties of the materials including viscosity, solubility, pH, refractive index, conductivity, dielectric permittivity, mechanical properties, etc.…”

“…Their conformational modifications induced by photo-or thermal isomerization of the azobenzene chromophore give the possibility to control some physical and chemical properties of the materials including viscosity, solubility, pH, refractive index, conductivity, dielectric permittivity, mechanical properties, etc. [1][2][3]12,16 Doping azobenzene compounds into polymer matrices is a convenient inclusion technique. Besides opportunity to use a presynthetized polymer the development of doped azobenzene systems become interesting for studying the behavior of chromophore and owing to the actual tendency to obtain composites with very small content of active component.…”

“…On the other hand, deviations from the first-order kinetics were found for the thermal relaxation of azobenzene moities in polymer matrices in glassy state. In this case the thermal back process has been described by two or three exponentials 3,12,17,18 or by the Kohlrausch-Williams-Watt stretched exponential model. 19 In the fundamental and applied chemistry maleimide derivatives are placed on an important place.…”