Precise Stepwise Synthesis of Donor-Acceptor Conjugated Polymer Brushes Grafted from Surfaces

Abstract

Donor-acceptor (D-A) conjugated polymers are promising materials in optoelectronic applications, especially those forming ordered thin films. The processability of such conjugated macromolecules is typically enhanced by introducing bulky side chains, but it may affect their ordering and/or photophysical properties of the films. We show here the synthesis of surface-grafted D-A polymer brushes using alternating attachment of tailored monomers serving as electron donors (D) and acceptors (A) via coupling reactions. In such a stepwise procedure, alternating copolymer brushes consisting of thiophene and benzothiadiazole-based moieties with precisely tailored thickness and no bulky substituents were formed. The utilization of Sonogashira coupling was shown to produce densely packed molecular wires of tailored thickness, while Stille coupling and Huisgen cycloaddition were less efficient, likely because of the higher flexibility of D-A bridging groups. The D-A brushes exhibit reduced bandgaps, semiconducting properties and can form aggregates, which can be adjusted by changing the grafting density of the chains.