Helically deployed Au nanoparticles using block copolymer templates as chiral plasmonic monoliths

Abstract

This work aims to fabricate polymeric thin films with helically deployed gold (Au) nanoparticles by using self-assembled chiral block copolymers (BCPs*) with controlled helicity as templates, giving polymeric monolith with unique optical properties as chiral plasmonic thin film. Enantiomeric polylactide-based BCPs*, polystyrene-block-poly(L-lactide) (PS-b-PLLA) and poly-styrene-block-poly(D-lactide) (PS-b-PDLA) with disulfide junction are designed and synthesized, denoted as PS-ss-PLLA and PS-ss-PDLA, respectively. The helically deployed chemical junctions of the PS-ss-PLLA and PS-ss-PDLA thin films from the self-assembly of helix-forming BCPs* can give thiol end groups preferentially arranged in a one-handed helical fashion at the inner wall of nanoporous PS after hydrolysis of polylactide followed by reducing the disulfide into thiol. Au nanoparticles (Au NPs) with a size of 2-5 nm, resulting from reduction, can associate with the thiol end groups in the nanoporous PS, forming a helical disposition of Au NPs with specific handedness. As a result, circular dichroism (CD) signals of localized surface plasmonic resonance (LSPR) originating from the helical Au NP arrays with preferred chirality can be acquired from the polymeric monolith fabricated, giving appealing applications as chiroptical devices.