Hydrophobic gold nanoparticles coupled with fluorescent dyes: A smart tool for optoelectronic applications

• Synthesis of hydrophobic AuNPs functionalized with fluorescent organic thiols. • Preparation of AuNPs/poly(phenylacetylene) (PPA) nanocomposite blends. • Tunable photoluminescence properties upon excitation by different wavelengths. • Band gap reduction up to 2.15 eV for AuNPs/PPA 90/10 % wt. • Electrical conductivity increases of about 2.5 times compared with pristine AuNPs. In this work, gold nanoparticles (AuNPs) are functionalized with two different rigid, conjugated thiol ligands: (i) 9,9-didodecyl-2,7-bis(acetylthio)fluorene (FL) and (ii) 2-(anthracen-9-ylmethyl)thio)ethane-1-thiol (2AET). Functionalized AuNPs synthesis is carried out via a two-phase wet chemical reduction method, using NaBH 4 as a reducing agent. During the synthesis procedure, ligands are used in 2AET/FL mixture exploring different molar ratios. On freshly prepared samples, UV–Vis and DLS studies demonstrate the reproducibility of the synthesis method over the molar ratios investigated, with the 2AET/FL 1:2 molar ratio giving the most stable colloids up to one year of aging. Infrared spectroscopies (FTIR, Far-IR) and SR-XPS allow a deep surface AuNPs characterization, which show tunable photoluminescence upon excitation by different wavelengths. To exploit potential optoelectronic applications, the π-conjugated polymer poly(phenylacetylene) (PPA) is used to prepare nanocomposites with different AuNPs/PPA weight ratios (from 10/90 to 90/10 %wt.). Morphological studies carried out with AFM and HR-TEM show 4 nm quasi-spherical shape AuNPs uniformly blended within the polymer. The electric response is assessed onto spin-coated thin films (thickness ca. 4 nm). At the highest AuNPs amount, the band gap is reduced up to 2.15 eV with an increase in the electrical conductivity of about 2.5 times compared with AuNPs and PPA.