Synthesis, Characterization And Fluoresence Properties Of A Hyperbranched Supramolecular Polymer Controlled By Acid-base Reaction

In recent years, people combined supramolecular chemistry with polymer chemistry to build light-emitting polymer materials, photovoltaic polymers, biomedical polymers, polymer sensors which are based on the weak interactions between molecules, such as hydrogen bonding, electrostatic interaction, π-π stacking interaction, hydrophobic effect, and van der Waals force. This field is a hot spot in the research of polymers. Supramolecular polymers which are structured by these noncovalent interactions not only have the nature of the traditional polymers together with novel structures and properties. Due to the noncovalent forces that are dynamic, and these supramolecular polymers can respond to the changes of external conditions, such as temperature, pH, mechanical forces, illumination etc. Therefore, the supramolecular polymer materials have a wide range of potential applications in drug transport, chemical sensing, and shape memory materials. However, rare example was demonstrated using polymers grafted with both host and guest groups. Here, we report the fabrication of a supramolecular cross-linked polymeric network through a monomer bearing both dibenzo-24-crown-8(DB24C8) and dibenzylamine groups at the same time.We designed and synthesized a large π-conjugated molecular skeleton with four branches, and then symmetrically connected two dibenzo-24-crown-8 rings and two dibenzylamine groups on it to form an A2B2-type monomer that can be used to construct a cross-linked supramolecular polymer. After adding excessive hexafluorophosphoric acid(HFA) into the solution of the monomer, the dibenzylamine groups can be protonated under this acid condition to form dibenzylammonium(DBA) centers, which can be threaded into the rings of dibenzo-24-crown-8 through [N+-H···O] and [C-H···O] hydrogen bonds and π-π stacking interactions. Monomers become closer to each other in the process of host-guest recognition and gradually form a large supramolecular network. As we continue supplying the system with P1-t-Bu, the deprotonation has taken place on dibenzylamine groups. It destroyed the host-guest recognition, and then the supramolecular polymer network disassembles into monomers. During the transiting process of the supramolecular polymer network and monomer molecules, we can see the change of fluorescence intensities. It promotes the potential application value of supramolecular polymers in the materials.