Synthesis of size-controlled faceted pentagonal silver nanorods with tunable plasmonic properties and self-assembly of these nanorods.

Monodisperse size-controlled faceted pentagonal silver nanorods were synthesized by thermal regrowth of decahedral silver nanoparticle (AgNPs) in aqueous solution at 95 degrees C, using citrate as a reducing agent. The width of the silver nanorods was determined by the size of the starting decahedral particle, while the length was varied from 50 nm to 2 mum by the amount of new silver added to the growth solution. Controlled regrowth allowed us to produce monodisperse AgNPs with a shape of elongated pentagonal dipyramid (regular Johnson solid, J(16)). Faceted pentagonal particles exhibited remarkable optical properties with sharp plasmon resonances precisely tunable across visible and NIR. Due to the narrow size distribution, faceted pentagonal silver nanorods readily self-assembled into the 3-D arrays similar to smectic mesophases. Hexagonal arrangement in the array completely overrode five-fold symmetry of the nanorods. Overall, our findings highlight the importance of pentagonal symmetry in metal nanoparticles and offer a facile method of the preparation of monodisperse AgNPs with controlled dimensions and plasmonic properties that are promising for optical applications and functional self-assembly.