Synthesis And Properties Study Of Functionalized Platinum-acetylied Dendrimers

Highly branched and regularly repeating dendrimers have emerged to become a key element in the research efforts of scientists worldwide.Due to the advantages of highly branched,highly controllable structure and easy functionalization,dendrimers have been widely used in homogeneous and heterogeneous catalysis,drug drug-delivery,light energy harvesting,sensors and nanomedicine.Due to the unique photophysical and electrochemical properties of transition metals,metallodendrimers have potential applications in the fields of photophysics,photochemistry,electrochemistry,biology,and catalysis.Based on our previous study on platinum-acetylide chemistry,dithienylethene and organometallic rotaxane,we designed and synthesized a series of functionalized platinum-acetylide dendrimers.Firstly,a method for efficiently constructing dithienylethene dendrimers was developed,and the basic properties of photochromism and photochromic kinetics were studied.Secondly,the fluorophores such as porphyrin and tetraphenylethylene were modified at the core or periphery of the dendrimer to study the regulation of fluorescence by ultraviolet light and visible light.Finally,the organometallic rotaxanes were modified to the periphery of the platinum-acetylide dendrimers.The high-generation type II-A rotaxane dendrimers were designed and synthesized,and their optical properties were studied.In Chapter One,the development process of dendrimers were introduced.Then the application of metallodendrimers in the fields of organo-metallic catalysis,organic light emitting diodes,light-harvesting and medical drugs was reviewed.In Chapter Two,dithienylethene platinum-acetylide dendrimers were synthesized by using triethnylbenzene as the core and dithienylethene platinum-acetylide complex as the branch.The third generation dendrimers contain 21 dithienylethene units,which are the single molecules with the largest number of dithienylethene units so far.The dendrimers were well characterized with 1H NMR,31 P NMR and MALDI-TOF-MS.Upon irradiation with ultraviolet light(365 nm)and visible light(> 530 nm),the DTE platinum-acetylide dendrimers could be repeatedly transformed between the ring-open and ring-closed forms.Steady-state absorption spectroscopy and transient absorption spectroscopy kinetic studies indicated that each photochromic unit of the dendrimers was independently switched.Theoretical calculations indicated that the benzene core preventing effective energy transfer between the photochromes due to the twists between the phenyl rings and platinum-acetylide units.This result provides a new idea for the research of information storage materials.In Chapter Three,the porphyrin dithienylethene dendrimers were synthesized by using zinc porphyrin as the core and dithienylethene platinum complex as the growth unit.The porphyrin DTE dendrimers could be repeatedly transformed between the sky blue color and light yellow color by alternate UV(365 nm)and visible-light(>530 nm)irradiation,accompanied by red fluorescence quenching and regeneration.As the generation of dendrimers increased,the rate constants of both cyclization reaction and cycloreversion reaction increased,indicating that photochromic and fluorescence regulation properties were enhanced.The introduction of the zinc porphyrin units imparts fluorescence regulation properties of metallodendrimers.In Chapter Four,tetraphenylene dithienylethene dendrimers were synthesized by using tetraphenylene as the core and dithienylethene platinum complex as the growth unit.The dendrimer exhibits AIE luminescence in a mixed solvent of dichloromethane and methanol.Under the illumination of ultraviolet light(365 nm)and visible light(> 530 nm),AIE luminescence was quenched and regenerated.The introduction of the TPE units imparts fluorescence regulation properties of metallodendrimers.In Chapter Five,tetraphenylene dithienylethene dendrimers were synthesized by using triethnylbenzene as the core and dithienylethene ethylene platinum complex as the growth unit.Upon irradiation with ultraviolet light(365 nm)and visible light(> 530 nm),AIE luminescence was quenched and regenerated.Comparison with the dendrimer of the tetraphenylene core further demonstrated the superiority of the multi-substituted dithienylethene dendrimers.In Chapter Six,the type II-A rotaxane dendrimers were synthesized with triethnylbenzene as the core,platinum complex as the growth unit and organometallic [2]rotaxane as the periphery.To the best of our knowledge,this is the first example of high-generation(more than two generations)type II-A rotaxane dendrimer.The structures were well characterized by 1H NMR,31 P NMR and MALDI-TOF-MS.The studies on AFM,TEM,DLS,and UV-visible spectroscopy indicated that the particle size and the absorption coefficient increased with the growth of dendrimer generations.