Liquid-Crystalline Organic-Inorganic Hybrid Superlattice: Development of Light-Controllable Metamaterials

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Nanoparticle (NP)-based periodic structure formation has attracted a considerable attention as metamaterials. Among organic soft materials, liquid-crystalline (LC) organic dendron is one of the most representatives to form spherical dendrimer-like structures by the self-assembling property. Thus, we focused our attention on introduction of such self-organization ability into inorganic NPs. As dendrons, we synthesized phenetyl ether-type dendrons G1-G3 with an amino-group at the apex. G1-G3 themselves show thermotropic LC phases. The dendrons are attached as the outer corona, through amidation, to the carboxylic groups at the surface of the inner aliphatic corona encapsulating the NP. Purpose-designed CO_2H-modified monodisperse gold NPs A1-A3 were synthesized uisng 12-dodecanethiol (DT) and 16-mercaptohexadecanoic acid (MHA). SAXS measurement revealed that G2-modified A2 showed an LC hexagonal columnar phase at 130 ℃ and formed a simple cubic (SC) LC phase at 150 ℃. The dendron-modified gold NPs G/A can be regarded as organic-inorganic hybrid dendrimers with thermotropic LC behaviour. The technique also applied to CdS NPs., and emission-quenching behavior by control of the self-organized structure was observed. Such behavior can be applicable for the development of NP-based novel-type of metamaterials.