From luminescent π-conjugated macrocycles to bridged multi-cyclic π-conjugated polymers: cyclic topology, aggregation-induced emission, and explosive sensing

Abstract

Topology is a unique dimension for macromolecular engineering, which has continuously spurred the creativity in synthetic chemistry to explore the boundary of the possible topology and architecture adopted by polymers. The successful synthesis of these topological polymers with a complex macromolecular architecture further provided unconventional polymer materials with intriguing properties and functions. Herein, a series of bridged multicyclic conjugated polymers are synthesized by the Yamamoto polymerization with telechelic conjugated macrocycles as monomers, and their chemical identities are further confirmed by nuclear magnetic resonance spectroscopy and gel permeation chromatography. Additionally, the bridged multicyclic backbone directly visualized by scanning tunneling microscopy at the highly oriented pyrolytic graphite interface has unambuguously confirmed the topology of polymers with a discrete ring of the cyclic monomer as the comparison. Similar to their cyclic monomers, these multicyclic conjugated polymers all exhibit aggregation-induced emission properties with intense emission as nano-aggregates or solids due to the existence of the tetraphenylethene moiety in the multicyclic scaffold. The fluorescence of these multicyclic polymers can be efficiently quenched by picric acid in aqueous media which proceeded via the static quenching mechanism with the photo-induced electron transfer process involved.