Study On The Light Controlled Reversible Self-assembly

Supramolecular chemistry is based on the non-covalent interaction between moleculars.Molecular self-assembly,which is the most important area in suprachemistry, means spontaneous building-up of complex structures via intermolecular interaction, from various building blocks including inorganic and organic molecules and macromolecules.Etc.The host-guest inclusion plays an important role among all kinds of driving forces leading to self-assembly.Cyclodextrins(CD) is one of the most important host molecules in supramolecular chemistry and have been fully researched.In recent years,our group has developed "block-copolymer-free" strategies to fabricate polymeric micelles using polymer pairs as building blocks.These novel approaches result in noncovalently connected micelles(NCCM),in which intermolecular specific interactions(hydrogen bonding and hydrophobic interaction etc.) rather than chemical bonding exist between the shell and core.Being a substantial progress in the studies on NCCMs,in this dissertation we prepared micelles utilizing inclusion complexation between CDs and azobenzene.The dissertation is consisted of following parts.Firstly,we synthesized a series of azobenzene containing hydrophobic small molecules via four-step organic synthesis.In the selected solvents,we successfully constracted micelles by adding the hydrophobic molecule solution toα-,β-CD ware solution at certain temperature.TEM,DLS,SEM studies were carried out to confirm bilayer vesicle structure of aggregates which has average diameter of 200nm.When the aggregates were irradiated by certain intensity of UV light,the morphology of aggregates changed.TEM images showed that the bilayer structure converted to irregular aggregates. Following DLS measurements unfolded the obvious change in both particle scale and PDI index.The research on the mechanism of self-assembly tells us that the conformation of azobenzene will shift from trans to cis being irradiated by UV,which will exclude from CD cavity results in disassembly of vesicle formed irregular aggregates.When employing Visible light to irradiate UV-irradiated aggregates,we found that the transformation of Azobenzene group from cis to trans make the morphology of the aggregates changed from irregular aggregates to bilayer vesicles,whose shell have the average thickness of 10nm.We succesfully constracted NCCM via inclusion complexation and realized reversible conversion between vesicles and irregular aggregates with light stimuli.The second part of my work is the extension of previous work.We synthesized dendrons with Azo head groups as hydrophobic building blocks.We have succefully synthesized three kinds of Azo-dendrons with different generations G1-Azo,G2-Azo,G3-Azo.Then we modifiedβ-CD at 6-position and obtained mono-substituted OTs-CD. We successfully prepared EDA-CD using Mono-OTs-CD and ethane-1,2-diamine as reactant,the product can further react with 2-chloropropanoyl chloride formβ-CD ATRP initiator.Theβ-CD ATRP initiator can initiate the ATRP polymerization with monomer NIPAM,and formedβ-CD-PNIPAM as hydrophilic part.We found that THF can dissloved bothβ-CD-PNIPAM and G1-Azo.While the combined mixture ofβ-CD-PNIPAM and G1-Azo in THF were injected into water,micelle formed immediately.DLS measurements were employed to investigate the micelle solution and found that the average diameter of aggregates is 150～200nm and both the particle scale and PDI value would change with the increase of the concentration of the mixture solution.AFM and TEM were carried out and confirmed the morphology of the aggregates should be bilayer vesicle.In our opinion,the noncovalent inclusion complexation is the driving force to impel the Azobenzene part of G1-Azo into the cavity ofβ-CD,and formed amphiphilic molecule by noncovalent interaction.The interaction between dendrons can self-assemble to form bilayer vesicle and the structure can be stabilized by the hydrophilic PNIPAM.Subsequently we used UV and Vis light to irradiate the micelle respectively and realized the reversible change between hollow sphere to solid aggregates.In short,we have successfully synthesized block copolymer with noncovalent interaction and achieved reversible conversion between vesicles to irregular aggregates by light stimuli.The third part of my work is mainly focus on the synthesis research on the dendrimer built by noncovalent interactions.In recent years,dendrimers became the research interest in organic,macromolecular and material chemistry.However the dendrimers built up by inclusion complexations have not been reported yet.In our work, we designed two kinds of monomer A and B as building blocks.The monomer A consisted of one azobenzene and twoβ-CD;while The monomer B consisted of one adamantane and twoα-CD.Adamantane can be included inβ-CD easily and azobenzene is prone to be enclosed in the cavity ofα-CD in water.The noncovalent alternate dendrimer molecule can be formed by adding A and B respectively in water.The UV and Vis light irradiation would make the dendrimer molecule reversibly disassembly and assembly.The organic synthesis work is still in progress.The fourth part of my work is search on the microwave assisted synthesis of di arylsulfones and Aryl-alkyl sulfones.The microwave assisted coupling reaction of electrondeficient aryl halides with sulfinic acid salts through SNAr-based addition reactions to form diarylsulfones and Aryl-alkyl sulfones.By screened conditions,we synthesized 17 derivatives with high yield and shorten the reaction time from 16 hours to 10 minutes compared to the direct heating method.In the reaction using sodium methanesulfinate and 2-fluorobenzonitrile as reactant,we had discovered new product, and put forward the mechanism.