Thiol stabilized extremely small gold cluster complexes with high photoluminescence

Abstract

Extremely small gold cluster complexes were synthesized by slowly reducing Au(III) to Au(I) in 1/1 mixed ethanol and toluene solvents in the presence of three times excess strong binging thiol ligand. The synthesized gold cluster compounds were fully characterized using different analysis techniques (mass spectrometer (MS), IR, UV–vis, PL, thermogravimetric analysis (TGA), elemental analysis (EA) and X-ray photoelectron spectroscopy (XPS)). The investigated compounds, (C4H9SAu)n, with the 1-butanethiol ligand (1), (C6H13OSAu)n with the 6-mercapto-1-hexanol ligand (2), (C12H25SAu)n with the 1-dodecanethiol ligand (3) and (C6H5SAu)n with the benzenethiol ligand (4), were characterized based on elemental and thermogravimetric analyses. Only tiny dimer and trimer of Au2 and Au3 can be detected from Mass Spectroscopy (MALDI-TOF) indicating n = 2 or 3. The isolated light yellow solid samples of 1–4 all show high luminescence under UV light. PL emission is limited to the 550 to 700 nm range in solution but the full emission between 550 and 850 nm is detected for the solids using different instrument. PL property dependence was seen for the capping thiol ligands, such that PL was red-shifted with increasing carbon chain length or with a conjugated aromatic ring. DFT calculations for the model structures demonstrate that these tiny gold-thiol clusters in either terminated or bridged thiol bonding modes are stable structures.