A Visible-light-induced Dynamic Mechanical Bond As New Linkage For Strcutural Dynamic Materials

The introduction of dynamic bonds such as the dynamic covalent or coordination bonds into the polymeric networks can produce structural dynamic materials with properties such as self-healing,recyclability,tunable stiffness and shape memory etc.Since the nature of the dynamic bonds has great impact on determining the properties of the dynamic materials,the exploration of new dynamic bonds becomes one of the core research areas in the field of dynamic materials.Besides chemical bonds,the mechanical bond（MB）,as a physical bond,has provided another accessible means in constructing molecular entities including rotaxanes and catenanes.However,the current research on mechanical bonds mainly focuses on the dynamics of the mechanical interlocking molecular structure itself,as well as the resulting properties and functions,but little attention is paid to the dynamics of the mechanical bonds themselves（which can be reversibly formed and broken）.In this dissertation,the concept of dynamic mechanical bond（DMB）is initially proposed,based on which a visible light induced DMB is designed and constructed,and further applied as new linkage for structural dynamic materials.Firstly,a[2]rotaxane consisting of the dumbbell-shaped axis with1,5-dioxophthalene（DNP）unit as recognition site interlocked by a electron-deficient tetravalent macrocycle(CBPQT⁴⁺)was designed and synthesized.Visible light induced photoisomerizable ortho-fluoroazobenzene unit was introduced at the end of the axis to play the role of stoppering group.Upon alternatively irradiating by visible lights,the reversible Z/E photoisomerization of the azobenzene unit can be triggered,thereby regulating the shuttle energy barrier of the CBPQT⁴⁺ring by changing the the steric hindrance of the stoppering group.This enables the DMB to exhibit unique visible light induced dynamic de-/reformation of mechanical bonds.The visible light induced dynamic bonding behavior of this DMB was systematically investigated,after which the application of such DMB as a new type of dynamic linkage was further explored by fabricating a DMB-crosslinked supramolecular polymer gel.It was found that the obtained DMB-incorporated gel was capable of exhibiting unique visible light-induced dynamic properties.In light of that the working mechanism of this light-induced DMB is distinguished from the currently available dynamic chemical bonds,the establish of such DMB can not only provide a new strategy for the construction of new dynamic bonds,but also develops a new dynamic bonding method for the preparation of dynamic materials such as self-healing polymers,vitrimers,dynamic interfaces,and so on.