The Study Of The Z-to-E Isomerization Proecess Of Azobenzene Derivatives In Different Media

Azobenzene(AB)derivatives exhibit a reversible isomerizarion process between two geometric isomers,E and Z,respectively.The maximum absorption wavelength,geometry structure(end-to-end distance),and energy difference between Z and E isomers of AB derivatives will be changed when it is irradiated with different wavelengthes of light,suggesting its potential applications into molecular switches,molecular machines,energy storage devices.In this thesis,the reactive molecular dynamics(RMD)simulations and density functional theory(DFT)were employed to investigate the effects of different substituents,solvents and black phosphorus substrate on the Z-to-E isomerization process of AB derivatives.The UV-vis spectroscopy techniques were employed to test some of theortical predictions and provide information for designing new photoresponsive materials.Prospects of the applications of the AB derivatives in biomedical field were also discussed.The results are summarized as follows:1.The effects of different substituents on the electronic structures of azobenzene.The effects of para-or ortho-substitution on the electronic structure properties of AB derivatives are investigated by introducing electron push/pull or long alkyl group with different lengthes into the skeleton of azobenzene.Four classes of para-substituted AB derivatives(AB-OC4H8-R)with different terminal groups(AB-1:R=NMe3+I-;AB-2:R=NH2;AB-3:R=C6H13;and AB-4:R=SH)and two classes of AB derivatives with ortho-substitution(AB-5:ortho-Methyl Red;AB-6:Calcon)were selected.The para-substitution has no significant effect on the UV-vis absorption spectrum and the rate of thermal relaxation.The introduction of the ortho-substituent breaks the planarity of the molecule,hence leads to the red-shift of the maximum absorption peak,?max,of UV-vis absorption spectrum.By increasing the number of ortho-substituents,the position of?max in the UV-vis absorption spectrum is further red-shifted.By changing the type,number and position of the substituents,the precise regulation of the absorption peak and the rate of Z-to-E thermal relaxation can be achieved,which is crucial to broaden the applications of azobenzenes in the biological field.2.Solvent effects on spectra properties and Z/E isomerization process of azobenzene derivativesSolvent has significant effects on the process of Z-to-E isomerization of AB derivatives.The difference between the rates of the Z-to-E isomerization of the same AB in different solvents could be as large as 106.We carried out RMD simulations to study the Z-to-E isomerization behavior of para-and ortho-substituted AB derivatives in different solvents(water,dichloromethane and dimethyl sulfoxide).For the para-substituted AB derivatives,there is no significant difference in the isomerization rate of the AB systems with different terminal groups in dimethyl sulfoxide(DMSO)solvent.The experimental Z-to-E isomerization rate of AB derivatives with thiol group(AB-4)in nonpolar dichloromethane solution(9.4×10-6 s-1)is 3.4 times faster than that(2.8 × 10-6 s-1)in polar DMSO.For the ortho-substituted azobenzene system,the isomerization behavior is hindered to some extent due to the presence of intramolecular hydrogen bonding interaction.After reaching the equilibrium conformation,the torsion angle appears to fluctuate greatly,indicating that the geometric structure changes significantly in solutions.In the calcon molecule,the coexistence of dynamic bonding interactions,hydroxyl group and the azo chromophore causes the multi-stimuli responsiveness to external stimuli including temperature,pH-variation and light-irradiation.The intramolecular proton transfer between the ortho-substituted hydroxyl group and nitrogen atom in the azobenzene brige is barrierless,which is favourable to induce azo-hydrazone tautomerism at body temperature(311K).The intermolecular and intramolecular hydrogen bonding interactions promote the azo-hydrazone tautomerism between the aromatic azo structure and the quinoid hydrazone structure in different pH conditions.The hydrazone form with typical quinoid structure property will enhance the n??* transition by the smaller HOMO-LUMO gap and larger degree of electron delocalization than those in azo form.The strong absorption in the visible light region,multi-stimuli responsiveness and good biocompatibility of calcon broaden its application in the biological field and achieve the multi-stimuli responsiveness in a single molecule.3.The Z/E isomerization behavior of the complex of liquid phase exifolated black phosphorus and azobenzene derivatives and its biological application.The ability to modulate the Z/E isomerization of AB derivatives is crucial to the practical applications in biological and photofunctional systems.We have invstigated the Z-to-E isomerization behavior of AB derivatives on the black phosphorus by theoretical and experimental methods.For the black phosphorus system,the binding energy calculated by DFT shows four classes of AB derivatives with different terminal groups(AB-1:R=NMe3+I-;AB-2:R=NH2;AB-3:R=C6H13 and AB-4:R=SH)and black phosphorus substrates have strong binding interactions.The quaternary ammonium salt derivative(AB-1)with R=NMe3+I-terminal group shows the most significant charge transfer between the AB derivatives and the black phosphorus.Theoretical calculations predicted that activation energy of Z-to-E isomerization of the AB@BP system is reduced from 1.0 eV to 0.8 eV,which was supported by our experiments.In the temperature range of 293K-313K,UV-vis spectroscopy measurements show that the isomerization rate of the AB@BP is 3?13 times faster than that in the free standing AB.RMD simulations also show that the reverse isomerization time of the AB@BP is about three times faster than that of free-standing AB.In comparision with the black phosphorus nanomaterials alone,the AB and black phosphorus complexe(AB-2@BP)displayed the best anticancer activity aginst human cervical cancer cells(HeLa)and human lung cancer cells(A549),which caused the production of cellular reactive oxygen species and induced apoptosis in cancer cells.Proteomics profiling identifies the ribosome as the target of AB-2@BP in HeLa.The AB-2@BP complex exerts anticancer effects by affecting the function of ribosomes,providing guidance for further application of the AB@BP hybrids in the biological field.