Gold nanoparticles with unsaturated heteroatom ligands

Gold nanoparticles (AuNPs) have been of great interest over the last decades due to their widespread applications in organic synthesis as catalysts and biomedical areas for imaging and drug delivery systems. This project proposal describes the fabrication, characterization and evaluation of potential applications of gold nanoparticles grafted with pi-conjugated molecules. These stabilizers should have a significant impact on the surface plasmon resonance, which is one of the most important optical parameters of AuNPs. The band gap and the orbital overlap of the ligands with the AuNPs will be crucial for potential applications of these materials as photo-responsive devices with significant conductance along the overall pi-systems which are linked by AuNPs. On the one hand, lowering the band gap of these pi-materials will be achieved by selective replacement of carbon atoms with heavier elements. For this purpose phosphorus atoms will be chosen as the dopant in the backbone of the pi-systems. In view of the close diagonal relationship of carbon and phosphorus - as outlined in the book "Phosphorus, the carbon copy" - in some aspects similar (chemical-) reactivity will be expected, while the pi-orbital of the P=C has a tremendous influence on the HOMO-LUMO separation. Furthermore the introduced phosphorus atom will also serve as the anchoring group - coordination site - on the AuNP surface. Owing to fact that the coordinating P-lone pair directly interacts with the adjacent conjugated pi-system a significantly enhanced charge transport along the AuNP-ligand junction is expected. Combining both aspects should lead to novel nano-materials with unprecedented opto-electronic properties. A special attention during this project will be devoted to physico- chemical studies of the targeted coated nanoparticles. Characterization of size and shape of the AuNPs by means of microscopy (e.g. SEM) will be complemented by conductivity measurements of the attached ligands i.e. by means of trapping AuNPs through dielectrophoresis in a nanogap and subsequent acquisition of current-voltage (I-V) curves. Different computational methods (HF, DFT, MD) will be chosen to get a deeper understanding on the nature of the free ligand (conjugation along the pi-system(s), optical properties, NMR chemical shifts) in comparison with the coordinated phosphanes (orbital overlap at the ligand:AuNP junction, charge separation, live times of excited states and changes in the fluorescence behavior). A successful integration of pi-conjugated phosphorus doped ligands on the surface of AuNPs might reveal fascinating opto-electronic properties, opening avenues for novel uses of gold nanoparticles in imaging and opto-electronic sensor applications.