Strongly luminescent films fabricated by thermolysis of gold-thiolate complexes in a polymer matrix

We present a simple method for the fabrication of highly luminescent gold-containing films by thermal decomposition of gold(I) dodecylthiolate synthesized by treating an ethanol solution of gold tetrachloroauric acid with an ethanol solution of 1-dodecanethiol. During the heat treatment of gold(I) dodecylthiolate complexes homogeneously distributed in the polystyrene matrix, extinction spectra of the films change from the well resolved spectrum of a gold(I) thiolate complex peaked at 390 nm to the broad Plasmon peak of metallic gold centered around 600 nm. All samples, both before and after heat treatment, show a strong red emission, with a maximum in the spectral range of 620-640 nm. The room temperature emission quantum yield strongly increases from the nonheated films to the briefly heated films reaching a value of ~8%, and decreases for the samples where larger gold particles are formed after prolonged heating. Transmission electron microscopy shows the occurrence of monodisperse gold nanoparticles with 1.8 nm mean diameter in the polymer matrix. Extended heat treatment leads to the partial coalescence of these nanoparticles into larger particles of irregular shapes, with a size in the range of 10-200 nm. We explain these findings by the formation from the original luminescent Au(I)-thiolate complexes of an emissive species with even stronger luminescence. This species is consumed in the growth of larger Au particles upon further heating. From the spectroscopic data, the strongly luminescent species could be few-atom thiolated Au clusters or polynuclear Au(I)-thiolate complexes with strong aurophilic interactions.