DNA-Enabled Chiral Gold Nanoparticle-Chromophore Hybrid Structure with Resonant Plasmon-Exciton Coupling Gives Unusual and Strong Circular Dichroism.
Xiang Lan, Xu Zhou, Lauren A McCarthy, Alexander O Govorov, Yan Liu, Stephan Link
Author Information
Xiang Lan: Department of Chemistry , Rice University , 6100 Main Street, MS 60 , Houston , Texas 77005 , United States.
Lauren A McCarthy: Department of Chemistry , Rice University , 6100 Main Street, MS 60 , Houston , Texas 77005 , United States.
Alexander O Govorov: Institute of Fundamental and Frontier Sciences , University of Electronic Science and Technology of China , Chengdu 610054 , China. ORCID
Stephan Link: Department of Chemistry , Rice University , 6100 Main Street, MS 60 , Houston , Texas 77005 , United States. ORCID
Circular dichroism (CD) from hybrid complexes of plasmonic nanostructures and chiral molecules has recently attracted significant interest. However, the hierarchical chiral self-assembly of molecules on surfaces of metal nanostructures has remained challenging. As a result, a deep understanding of plasmon-exciton coupling between surface plasmons and chiral collective molecular excitations has not been achieved. In particular, the critical impact of resonant plasmon-exciton coupling within the hybrid is unclear. Here, we employed DNA-templated strategies to control the chiral self-assembly of achiral chromophores with rationally tuned exciton transitions on gold nanosphere (AuNP) or gold nanorod (AuNR) surfaces. Unlike many previous chiral plasmonic hybrids utilizing chiral biomolecules with CD signals in the UV range, we designed structures with the chiral excitonic resonances at visible wavelengths. The constructed hybrid complexes displayed strong chiroptical activity that depends on the spectral overlap between the chiral collective molecular excitations and the plasmon resonances. We find that when spectral overlap is optimized, the molecular CD signal originating from the chiral self-assemblies of chromophores was strongly enhanced (maximum enhancement of nearly an order of magnitude) and a plasmonic CD signal was induced. Surprisingly, the sign of the molecular CD was reversed despite different self-assembly mechanisms of the Au nanoparticle-chromophore hybrids. Our results provide new insight into plasmonic CD enhancements and will inspire further studies on chiral light-matter interactions in strongly coupled plasmonic-excitonic systems.
