Nanocluster superstructures or nanoparticles? The self-consuming scaffold decides

Abstract

We show that using the same reaction procedure, by hindering or allowing the formation of a reaction intermediate, the Ag⁺dodecanethiolate polymeric complex, it is possible to selectively obtain Ag dodecanethiolate nanoparticles or Ag dodecanethiolate nanoclusters in the size range 4–2 nm. Moreover, the Ag dodecanethiolate nanoclusters display a lamellar superstructure templated from the precursor Ag⁺dodecanethiolate polymeric complex. A plausible formation mechanism is illustrated where, starting from the precursor and scaffold lamellar Ag⁺ thiolate polymeric complex, first the nanocluster Ag_n⁰ core is formed by reduction of isoplanar Ag⁺ ions, followed by Ag⁺ thiolate units that build protection, the nanocluster shell, around the core. The nanoclusters are characterized by elemental analyses, XRD, ATR-FTIR, XPS, XAS, MALDI, ESI, UV-Vis and fluorescence measurements. The luminescent Ag₁₅(dodecanethiolate)₁₁·2H₂O nanocluster is achieved in good yield after 4 hours of reaction whereas after 2 hours, the luminescent Ag₃₅(dodecanethiolate)₁₆ is isolated. Both Ag nanoclusters present emission bands in the range 330–450 nm, the shifting depending on the excitation wavelength. This phenomenon is attributed to a possible dipolar state causing distribution in energies due to variability of dipole–dipole interactions. Moreover, both nanoclusters further present a NIR emission at about 700 nm independent from the excitation wavelength. Thanks to their optical and structural properties, the synthesized nanoclusters, perfect molecular/nanoparticle hybrids, have great potentiality for new applications in nanotechnologies.