Reversible constitutional switching between macrocycles and polymers induced by shape change in a dynamic covalent system

Abstract

We report here the development of morphological switches as a new tool that can be used in constitutional dynamic chemistry (CDC) to control the constitution of the whole dynamic system. Molecules that have well-defined but switchable shapes were designed and synthesized. Their restrained conformational states were characterized both in the solid and in solution. The addition of metal ions induces a shape change through coordination; the shape generated was also fully investigated both in the solid and in solution. Such molecules constitute morphological switches, meaning that they can explore various shape states as a result of controlled well-defined shape changes triggered by an effector. These morphological switches were then integrated into covalent dynamic systems through formation of reversible imine bonds. Thermodynamic and kinetic analyses were performed in order to quantify the covalent equilibrium and to investigate the labile character of the covalent reversible link. It was then demonstrated that the molecular shape state of the morphological switches induces a well-defined constitution through covalent self-assembly, and that the system can be steered, quantitatively and reversibly without significant fatigue, between two different constitutional states, respectively, polymeric and macrocyclic assemblies. The dynamic covalent polymeric assemblies were analysed by DOSY NMR and small angle neutrons scattering (SANS). Their dynamic behaviour as a function of the concentration and the temperature was demonstrated and characterized.