No abstract

Gold nanorods (Au NRs) present unique optical and electronic properties that depend on their morphology. Their applications in sensing and therapeutics require easy syntheses with a precise control over their dimensions. Here, we report a method for the synthesis of highly pure and monodisperse Au NRs with fine-tuneable dimensions and longitudinal localised surface plasmon resonance by addition of Hofmeister salts into the growth medium. The control of Au NR formation relies on the double interaction between the salt-gold and salt-surfactant (cetyl trimethylammonium bromide, CTAB). With the addition of Hofmeister salts (i.e. NaNO3, NaBr, NaCl and NaHSO4) we can fine-tune the aspect ratio of Au NRs in the range of 3.3 to 4.8 with a precision of 0.1 and the longitudinal adsorption band from 777 to 960 nm. In addition, we have studied the physical changes of the CTAB micelles induced by the salts using rheology, microscopy and lightscattering techniques. We report for the first time electron microscopy imaging of the micelles under Au NR growth conditions. With the comprehensive characterization of CTAB micelle in the growth solution, this study provides a deeper understanding of the anisotropic growth of metallic crystals. have low affinity for gold, like nitrate, bisulphate and chloride, their addition yields longer aspect ratio rods. However, anions with high affinity for gold, like bromide, reduce the gold deposition, producing shorter aspect ratio rods. Interestingly, CTAB micelles are mainly sphere-shaped in all solutions. The addition of salt increases the overall micelle size by increasing the non-spherical micelle population, although spherical shape is still the predominant one. Hence, these results provide not just a new strategy for the precise tuning of the optical properties and morphology of Au NRs, but also a deeper understanding of the anisotropic growth mechanism of the nanoparticles.

The sigma (s)-hole effect has emerged as apromising tool to construct novel architectures endowed with new properties.Asimple yet effective strategy for the generation of monofluoromethyl radicals is acontinuing challenge within the synthetic community.F luoromethylphosphonium salts are easily available,air-and thermally stable,aswell as simple-tohandle.H erein, we report the ability of the s-hole effect to facilitate the visible-light-triggered photolysis of phosphonium iodide salts,acharge-transfer complex, selectively giving fluoromethyl radicals.T he usefulness and versatility of this new protocol are demonstrated through the mono-, di-, and trifluoromethylation of av ariety of alkenes.Scheme 1. The application of s-hole effect of pnictogen atom.