Studies On The LCST Behavior Of The Supramolecular Macrocycles

Supramolecular chemistry has received extensive attention since its development,and has become the most popular research object in the field of advanced functional materials.In the field of advanced functional materials,stimuli-responsive supramolecular materials are a type of rapidly developing supramolecular adaptive materials which capture small changes in the external environment quickly.The dynamic and reversible non-covalent bonds in supramolecular assemblies are susceptible to temperature.Therefore,the thermo-responsive supramolecular materials are an important research object of current stimuli-responsive materials.In addition,supramolecular macrocycles are currently the main research objects of supramolecular systems which have unique cavity structures and electron-richness with different strengths.In this thesis,the LCST properties of the supramolecular macrocycles and the regulation methods of the LCST behavior are studied.In the first part,the LCST behavior of structurally modified benzo-21-crown-7(B21C7)monomer was studied.Different lengths of hydrophobic alkyl chains were introduced into the B21C7 monomer by using urea bond or carbamate bond as the linkages.From experiments,we found that the LCST behavior of the monomer was related to the length of hydrophobic alkyl chain.The longer the length of alkyl chain is,the lower the phase transition temperature becomes.At the same time,we also found that the type of the linkage has a significant effect on the thermo-sensitive properties of the monomer.Since amide groups are more hydrophilic compared with ester groups,it is reasonable that crown ethers with urea-based linkers show higher phase transition temperature.Therefore,it is crucial to realize the balance between hydrophobicity and water solubility,wherein concentration and hydrophobicity are two key factors to control LCST behavior.In the second part of the work,a pillar[5]arene equipped with ten benzo-21-crown-7(B21C7)units PC10 was developed,and the LCST behavior of this monomer has been studied.From experiments,we found that the higher the concentration is,the lower the phase transition temperature becomes.In addition,the thermo-responsiveness of the monomer is not only controlled by the B21C7-involved host-guest interactions,but further manipulated by the pillar[5]arene-based supramolecular complexation.The addition of the cations or guests effectively reduce the phase transition temperature of the system.