Topology-controlled dynamic conjugated oligomers from tetra-arylsubstituted alkene building blocks.

Abstract

Topology plays an important role in polymeric materials. Herein, we present an iterative, modular approach for creating tetra-arylsubstituted alkene (TAA)-based dynamic conjugated oligomers with diverse topologies, using boronate-protected Suzuki-Miyaura coupling chemistry. The TAA building blocks involving spontaneous alkene isomerization are found to induce conformational dynamics in the conjugated backbones, exhibiting steric-controlled transitions. These transitions occur from a twisted backbone rich in cis-alkenes in the linear PL9 oligomer, to a stretched backbone with a trans-alkene center and multiple cis-alkene end in the three-armed planar PY12 oligomer and the four-armed 3D PX16 oligomer. Consequently, these topological oligomers exhibit distinct photoluminescence and photochemical properties depending on their physical state. Experimental characterization and molecular dynamics simulations (MD) reveal a topology-dependent adaptive self-assembly of helices: linear PL9 forms long flexible helical fibers with a pitch of 28 nm; planar Y-type PY12 oligomers often occur in neural-like networks, connected by nanofibers and cell-like central aggregates; and stereo X-type PX16 adopts short helical rod-like morphology with a mesoscopic pitch of 86 nm in crystalline phases. This work may inspire concepts and the practical construction of helical and neural-like fiber materials by altering unit topology in dynamic conjugated oligomers.