Preparation And Property Study Of Multidentate Thiol-containing Polymer-quantum Dots Composites

As novel fluorescent nanomaterials,quantum dots(QDs)have excellent fluorescent properties compared with traditional organic dyes,including wide excitation spectrum,narrow and symmetrical emission spectrum,high fluorescence quantum efficiency and so on.QDs have been extensively used in biosensing,fluorescence imaging,solar cells,display devices and etc.At present,there are two main routes for the synthesis of QDs: organic phase synthesis and aqueous phase synthesis.Although the preparation of QDs by organic route has been developed for a long time,many issues still exist,such as critical synthesis conditions,high cost,and high environmental pollution.In contrast,the QDs prepared by aqueous route have the advantages of simple synthesis,cheap reagents,and environmentfriendly solvent.However,the stability of aqueous phase QDs is not as good as organic phase QDs,which significantly influences their further application in biomedicine and optoelectrial devices.The weak stability of QDs mainly originates from the weak binding ability and limited binding sites of small thiol-containing molecules usually used as ligands during the synthesis of aqueous QDs.Hence,we design and synthesize of novel multidentate thiol-containing polymers and take the advantage of multidentate synergetic effects to enhance the stability of QDs and develop new surface modification techniques of aqueous QDs.This thesis focuses on the design and synthesis of novel multidentate thiol-containing polymer ligands to solve the stability issues of aqueous phase QDs.We designed and synthesized two novel polymers containing multiple thiols and developed novel surface modification techniques based on these polymers for the aqueous phase QDs.In the first part of this thesis,we designed and synthesized novel thiol-containing block-copolymer ligand P(AA-b-VBT)and used them to modify the surface of QDs.P(tBA-b-VBC)was synthesized by using reversible addition-fragmentation chain transfer polymerization(RAFT)and treated by certain protection and de-protection reactions to obtain the multidentate thiol-containing P(AA-bVBT).Then,this novel ligand was used to partially exchange the mercaptopropionic acid on the surface of aqueous phase CdTe/CdS QDs.The synergetic effects between thiols in P(AA-b-VBT),the hydrophobic interaction of the thiol groups block in the polymer,and the cross-linking between thiol groups can enhance the interactions of the polymer ligands with the QDs.The experimental results showed that the ultrafiltration stability and photostability of QDs after surface modification of P(AA-b-VBT)are significantly improved,which proves the effectiveness of using multidentate thiol-containing polymer ligands for the surface modification of aqueous phase QDs.In the second part of the thesis,we designed and synthesized a cationic type multidentate thiolcontaining polymer P(Sty-VBT-DMA),and prepared QDs-polymer membrane.First,a random copolymer P(Sty-VBC)was synthesized by using radical polymerization and was then converted to P(Sty-VBT-DMA)by quaternized reaction and thioacetic acid esterification.With the help of the electrostatic attraction from quaternary ammonium groups and the coordination interaction of thiol groups,QDs can be transferred from aqueous phase to organic phase and form polymer-QD complex,which was further used to prepare polymer-QD films.The experimental results showed that these films have better solvent stability and photostability than QDs modified by small molecule cationic surfactants.In this part of the work,we developed a surface modification method for aqueous phase QDs based on cationic type multidentate thiol-containing polymer,which provides a new method for the preparation of QDs-polymer films by using aqueous phase QDs.