Self‐assembly of Gold Nanoparticles into an Adjustable Plasmonic 3D Lattice using Janus‐type Forked Mesogenic Ligands

• Published in: Chemistry, an Asian journal an Asian journal, 2022-04, Vol.17 (8), p.e202200057-n/a
• Main Authors: Zhao, Yang‐yang, Cao, Yu, Siligardi, Giuliano, Mehl, Georg H., Liu, Feng, Ungar, Goran
• Format: Article
• Language: English
• Subjects: Azo compounds; Chemistry; Cholesterol; Dichroism; Gold; Gold - chemistry; Isomerization; Ligands; liquid crystal; Metal Nanoparticles - chemistry; Nanoparticles; photoisomerization; plasmonic resonance; Plasmonics; Superlattices; Three dimensional bodies
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202200057

We report the formation of a 3D body‐centred self‐assembled superlattice of gold nanoparticles whose interparticle gap, and hence its plasmonic properties, are adjustable exclusively in the xy‐plane. Thus, even though the particles are spherical, their anisotropic packing generates tailorable plasmonic dichroism. The gold nanoparticles are coated with forked ligands containing two mesogens: either two cholesterols (“twin”), one cholesterol and one azobenzene (“Janus”), or a mixture of the two. Beside the body‐centered arrangement of gold nanoparticles, the structure also contains unusual two‐dimensionally x‐y dual undulated (eggbox‐like) smectic‐like layers of mesogens. Moreover, the presence of azobenzene mesogens allows the superlattice to be melted through UV‐induced photo‐isomerization; the process is reversible displaying low fatigue on repeated cycling. Gold nanoparticles (NP) grafted with mixed‐mesogen forked ligands self‐assemble in a photoresponsive 3D superlattice with adjustable anisotropic plasmonic absorption. The gold NPs are arranged on a body‐centered tetragonal lattice intercalated by doubly‐modulated mesogens layers. Reducing graft density reduces the in‐layer NP distance enabling near‐field plasmonic enhancement. The attached azobenzene mesogen allows repeated photoinduced order‐disorder switching.