Study On The Properties Of Two-photon Isomerization And Iron Ion Sensor Based On Azobenzene Derivative

Azobenzene and its derivatives as a kind of photo-responsive material have attracted increasing attentions. Under the stimulus of UV light, they can undergo photoinduced trans–cis isomerization, associated with the change of colour, solubility, refractive index, polarity, etc. Based on their excellent optical response, azobenzene derivatives have been widely used in liquid crystal, nonlinear optics, holographic surface relief grating and optical data storage fields. In this thesis, we have studied the two-photon induced isomerization of a prepared azobenzene derivative, N-?3,4,5-octanoxyphenyl?-N'-4-[?4-hydroxyphenyl?azophenyl]1,3,4-oxadiazole?AOB-t8?. The selective recognition behavior and mechanism of AOB-t8 in sensing Fe³⁺ has been investigated as well.Specifically, the thesis consists of two parts as follows:In recent years, photoswitching azobenzene derivatives have attracted increasing attentions for their applications in biological and biomedical fields based on their photocontrolled reversible structure and function. However, most of the azobenzene-modified biomolecules require the UV light for isomerization, which limits their application in biological systems due to the UV light can be strongly scattered by cells or tissues and also can trigger apoptotic events or other unwanted responses. In order to address this challenge, considerable effort has been devoted by employing the longer wavelengths of light to induce isomerization. In the first part of this thesis, we investigated the two-photon induced isomerization and dynamical features of the prepared AOB-t8. The photoproduct of cis isomer was unambiguously identified by UV-visible absorption and fluorescence spectroscopy with the activation of two red photons. The two-photon absorption coefficient of AOB-t8 was obtained from nonlinear optical measurements. The rate constants of two-photon photochemical reaction were also obtained according to the integrated rate law.On the other hand, metal ion fluorescent sensors have attracted increasing interests in environmental, chemical and biological fields due to the inherent simplicity, highly sensitive and selective features. In recent years, a large number of works for the detection of Cu²⁺, Pb²⁺, Zn²⁺, and Hg²⁺ have been reported by monitoring the fluorescence properties of chemosensors. However, vanishingly few papers about azobenzene derivatives were reported in the application of fluorescent sensor for transition metals. In the second part of this thesis,we studied the recognition behavior and mechanism of AOB-t8 in sensing the metal ion Fe³⁺ The results demonstrate that the AOB-t8 can work as a highly selective fluorescent “turn-off” sensor in sensing Fe³⁺. The Fe³⁺ sensing of AOB-t8 is realized from the chelation of ferric ion with the azobenzene moiety, which was confirmed by FT-IR, Raman spectroscopy and Job's plot. The binding association constant of 6.07×10³ M^-1 was obtained from Stern-Volmer plot in ethanol. Interestingly, the photoisomerization property of AOB-t8 can be regulated by Fe³⁺. The chelation of Fe³⁺ accelerates the isomerization of AOB-t8 to UV irradiation. Moreover, the reversible sensing ability of AOB-t8 was successfully observed by releasing the iron ion in AOB-t8-Fe?III? with the addition of citric acid.In a word, the photoisomerization of AOB-t8 molecule induced by two-photon excitation have been studied, which will help to extend the potential applications of AOB-t8 acting as photoswitch in biomedical and biological fields. On the other hand, AOB-t8 has demonstrated a specifically selective response to Fe³⁺ ions, and the involved mechanism has been systematically investigated.