Janus-Type Gold/Polythiophene Composites Formed via Redox Reaction at the Ionic Liquid|Water Interface

Janus-type Au/polythiophene (PT) composites have been prepared by utilizing the liquid/liquid interface between water (W) and a hydrophobic ionic liquid (IL) as the redox reaction site. AuCl₄^- is reductively deposited, and terthiophene is oxidatively polymerized spacio-selectively at the IL|W interface, leading to the formation of the Au/PT composites. The composites are Janus-type Au-attached PT plates with two surface morphologies, flat surface and flowerlike surface at the W and IL sides of the plates at the IL|W interface, respectively. Not only surface morphologies but also attached Au structures are different at the two surfaces; Au microurchins on the flat surface and dendritic Au nanofibers on the flowerlike surface. Optical and scanning electron microscopic observations have revealed that nanofibers and microurchins are formed at the early and later stage of the reaction, respectively. Electrochemistry at the IL|W interface has illustrated that electron transfer across the IL|W interface during the formation of the Janus-type Au/PT composites is coupled with ion transfer of AuCl₄^- to compensate for the charge unbalance in the two liquid phases. AuCl₄^- transferred into IL is found to be the source of the dendritic Au nanofibers formed at the IL side of the PT plates.