PORPHYRIN NANO-ASSEMBLIES ONTO GOLD NANORODS

Gold nanoparticles (AuNPs) have attracted large interest due to their relatively easy syntheses and their peculiar shape and size dependent optical properties, which make them interesting nanomaterials for a variety of applications. In particular, gold nanorods (AuNRs) have been extensively explored in several fields, such as in catalysis, sensing, optoelectronics and biomedicine. Ordered assemblies in which electronic, magnetic and optical properties could be tailored through coupling among neighboring nanorods have been investigated in order to improve the properties of these nanomaterials. Self-assembling can be accomplished via supramolecular approach by functionalization with organic or inorganic components as well as biomolecules. The facile fabrication of linear chains of AuNRs and bifurcated junctions of nanorods/nanospheres has been achieved through crosslinking of AuNPs with a water soluble anionic porphyrin. Here, we report the interaction between tetrakis-(4 sulphonatophenyl) porphyrin (TPPS) and AuNRs in aqueous solution. This porphyrin shows the peculiar ability to self-aggregate forming extended J-type nano-assemblies which exhibit interesting nonlinear optical and optoelectronic properties mainly related to their structure.4,5,6 At rather mild acidic conditions nanohybrid assemblies composed of TPPS porphyrin J-aggregates and AuNRs has been obtained. Kinetics for the growth of AuNRs assemblies evidence dependence on porphyrin concentration. In particular, at high porphyrin load a fast process, i.e. a more pronounced shift of the longitudinal plasmonic absorption band of AuNRs, have been observed. A detailed spectroscopic investigation has been carried out using a combination of UV/Vis absorption, resonance light scattering and fluorescence emission techniques.