Environmental Sensitivity Of The Au(Ⅰ)-thiolate Lamellar Assemblies

Metal-organic coordination polymer(CP)is a new type of artificial supramolecular self-assembled material that has been developed in the past two decades.Due to its adjustable structure and easy synthesis,it has been widely used in many fields,such as drug release,gas adsorption,biological imaging and organic catalysis etc.Au(Ⅰ)-thiolate CP is a special kind of linear CP material.Similar to biological macromolecules,there are many kinds of weak interactions,such as coordination interaction,aurophilic interaction and inter-ligand interaction including hydrophobic interaction,H-bond,static interaction,Van der Waals’ force,and so on.Based on these interactions,they can further self-assemble into hierarchical double helixes or lamellae in aqueous or organic solutions,which represent a new type of bio-mimic material.The realization of the magical functions of biological macromolecules is closely related to their dynamic responsiveness to their microenvironment.it is a challenge to conveniently monitor the microscopic structural change of these biomolecules in different environments in real time.The commonly used structural resolution techniques such as single crystal X-ray diffraction,infrared,nuclear magnetic resonance are hard used for samples that is in colloidal states.in this context,Au(Ⅰ)-thiolate CPs can be used as a simple artificial model system for this aim because they have sensitive ligand to metal charge transfer(LMCT)and metal centered charge transfer(MCCT)absorptions in UV-vis absorption spectrum,and UV-vis spectroscopy can be applied as an efficient technique to monitoring the structural change in different environments.In this thesis,two types of Au(Ⅰ)-thiolate lamellae with different thicknesses and morphology as well as surface functional groups are used to study their spectral change upon external environment(such as temperature,solvent,etc.),and then to reveal the relationship between the assembly structure and the environmental change.We first investigated the temperature sensitivity of the Au(Ⅰ)-thiolate lamellar assemblies with UV-vis absorption spectroscopy.It’s found the LMCT and MCCT transition absorption in the UV-vis absorption spectra blue-shifts with the increasing temperature,and the blue-shifted of the LMCT transition absorption is not affected by its thickness,size and surface functional groups of the self-assemblies.In contrast,there is no significant temperature sensitivity of gold nanoparticles and some small organic molecules.So the temperature sensitivity has a close relationship to the weak interaction in the self-assemblies.In addition to the UV-vis absorption spectra,temperature-varying powder X-ray diffraction and atomic force microscopy were used to further reveal the structural change of dry assemblies with temperature,and these experiments did not show.At the same time,dynamic light scattering was used to monitor the changes of the assembly size at different temperatures,and there were also not any convincing changes in size.One reason is that their structure cannot change when they are separated from the original solvation environment and dried.The other reason is that the very small changes that cannot be detected with X-ray diffraction and atomic force microscopy can result in a huge change in UV-vis spectroscopy.This indicate that UV-vis spectroscopy is a powerful technique to reveal the tiny change in structure when other techniques failed in Au(Ⅰ)-thiolate system.Then we continue to use UV-vis absorption spectroscopy to monitor the solvent dependence of Au(Ⅰ)–thiolate lamellar assemblies.In different solvents,it is also found that the spectral changes of the assemblies are not directly related to the thickness and size of the assemblies.There is no obvious relationship between spectral change and the physical properties of solvent,such as polarity and protonic property,but the larger the organic solvent molecule is,the more shift of the spectra,So propose that the change of temperature and solvent affects the strength of the weak interaction of the selfassemblies which cause the slight expansion of the Au-S network backbones.In summary,UV-vis absorption spectroscopy is proved to be an effective method to monitor the environmental sensitive properties of Au(Ⅰ)–thiolate lamellar assemblies.The research provides a new way to monitor the structural changes of the sub-micron scale colloid materials.However,it is difficult to reveal the relationship between the self-assembly structure and the spectral change so far,some more theoretical calculation need to be research to assist our experiments.