THE EFFECT OF SUBSTITUENTS ON THERMAL AND OPTICAL PROPERTIES OF AZOBENZENE-CHOLESTERYL DERIVATIVES

Rathinam Balamurugan ； Zheng-Yung Huang ； Bo-Tau Liu

《Journal of Innovative Technology》 1卷2期 (2019/09) Pp. 69-75

https://doi.org/10.29424/JIT.201909_1(2).0011

摘要

Structurally isomeric cholesteryl-appended azobenzene derivatives with various substituents, such as H/unsubstituted, ether and ester, at the terminal position of azobenzene units were designed, synthesized and characterized spectroscopically. The effect of substituents on the thermal and optical properties of all the derivatives were studied. The results from thermogravimetric analysis (TGA) revealed that all the derivatives were stable up to 283 °C and start to degrade thereafter. In addition, the ether derivatives exhibited lower thermal stability than the other derivatives. It is likely that the presence of ether linkage at the terminal position introduced greater flexibility to the azobenzene and, consequently, reduced thermal stability. The ether and ester derivatives underwent two-stage decomposition when heated up to 600 °C; the first stage between 320-350 °C due to the breaking of ether and ester linkages, and the second stage between 440-490 °C due to the breaking of carbonate linker which connect azobenzene to the cholesteryl unit. However, the unsubstituted (H-substituted) derivative underwent only one-stage degradation at 386 °C due to the cleavage of the carbonate linker. Results from the differential scanning calorimetry (DSC) revealed that the melting transition temperature (T_m) of the ester derivative was higher than the other two, supporting the above-said phenomena of thermal stability. The photolysis of all the derivatives exhibited trans-cis isomerization when irradiated with UV light. The rate of photolysis of ether was faster (2 min) than both ester and the unsubstituted derivatives (5 min). These results revealed that substituents at the terminal position of azobenzene are able to influence thermal and optical properties under given conditions.

關鍵字

Azobenzene ； Cholesteryl derivatives ； Thermal properties ； Optical properties ； Photoisomerization

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