One pot hemimicellar synthesis of amphiphilic Janus gold nanoclusters for novel electronic attributes

A one-pot hemimicellar synthesis of oriented, amphiphilic, and fluorescent Janus gold clusters, establishing the Janus character in terms of ligand asymmetry and distribution, has been demonstrated. The method was based on the efficient Langmuir strategy, where the in situ two-dimensional (2D) reduction of Au(3+) in the sprayed micellar electrostatic complex, TOA(+)-AuCl(4)(-), was accomplished by subphase tryptophan that acted as the hydrophilic protecting ligand on one hemisphere of the spherical gold cluster. In contrast to the reported micelle-assisted Janus cluster formation, here the cluster growth occurred inside the surface pressure driven hemimicelles, which rapidly formed 2D cluster arrays without any interfacial reorientation. The Janus structure was validated using angle dependent polarized Fourier Transform Infrared Reflection-Absorption Spectroscopy (FT-IRRAS), where orientation dependent vibrational changes in the adsorbed ligand functionalities were detected. Electrochemical impedance measurements of the transferred Janus layers onto hydrophobized ITO revealed the heterogeneous electron transfer rate constant k(ET) to show a clear orientational odd-even parity effect with the odd layers showing much higher rates. Isobaric area relaxation investigations further evidenced toward a hemispherical instantaneous nucleation with edge growth mechanism of the nanoclusters formed at the tryptophan subphase. Surface pressure as a thermodynamic variable effectively controlled the interparticle separation; intercluster electron coupling exhibited insulator-metal transition in the Janus cluster monolayers through scanning electrochemical microscopy investigations.