Synthesis And Photoisomerization Behavior Of Azobenzene Derivatives

Azobenzene derivatives are one of typical photochromic materials, and its photoisomerization properties have been widely used in many areas. In this thesis, five azobenzene derivatives with different structures are designed and synthesized. The effects of its structure on the spectral properties are investigated in details. The obtained five azobenzene compounds are exploited for the modifications of inorganic quantum dots and graphene.Firstly, five azobenzene derivates are synthesized by the diazo coupling method. These compounds contain strong electron-withdrawing groups, electron donating groups and compounds containing different number of azo group. The methods such as oxidation of the amino, amino protection and reduction of nitro are also related during the synthesis. Their structures were characterized by FTIR and UV-Vis absorption spectra.Secondly, photoisomerization properties of azobenzene compounds have a relationship with the nature of the substituents on the molecular structure. Photoisomerization dynamics behavior of these derivates containing electron-withdrawing group -NO2, electron donating group -NH2, and different number of azo groups were compared and investigated. The results showed that the isomerization performances of the azobenzene compounds are related to their substituents. The isomerization process is inhibited by the electron-withdrawing group while the role of multiple azo groups is more complicated. In addition, the polarity and acidity of solvent have also a certain impact upon the UV-Vis absorption spectra of azobenzene compounds. The polar solvents affected the transition energies of electrons, resulting in displacement of λmax. The H+ in acidic medium causes protonating of the chromophore molecule, resulting in acidichromism.Thirdly, in order to modify inorganic quantum dots (QDs),4-aminoazobenzene which has excellent photoisomerization performance is combined with mercaptopropionic acid (MPA) by a condensation reaction of amidation. A novel azobenzene derivative (MPAA) is therefore synthesized, and its structure is characterized by 1HNMR, FTIR and UV-Vis spectrum. This compound and MPA are used as ligands to prepare CdSe-MPAA QDs. Compared with the CdSe QDs using MPA as a ligand, the novel QDs have photoisomerization properties in UV-Vis absorption spectrum, while the joined azobenzene molecules play fluorescence quenching effect to the CdSe QDs in fluorescence spectrum.Finally, with regard to the functional graphene oxide (GO), there are a large number of polar hydrophilic groups (-COOH) on the GO surface and they are combined with 4,4’-aminoazobenzene by amidation condensation reaction. The azobenzene molecules are grafted onto the surface of GO and hybrid material of GO-Azo is synthesized. This material has not only a basic structure of a monolithic layer of GO but also a photoisomerization behavior of azobenzene chromophore. The electrical conductivity of the GO-Azo is significantly increased, compared to the GO. It’s decreased gradually under UV irradiation and can be exploited for photoswitch of electrical conductivity.