Synthesis and characterization of binaphthalene-2,2′-diamine-functionalized gold nanoparticles

Gold nanoparticles 1.7 and 54 nm in diameters have been synthesized and functionalized successfully with their surfaces engineered using two atropisomeric capping ligands, 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene (BINAP) and 1,1′-binaphthalene-2,2′-diamine (DABN), respectively. A systematic study to compare the two different gold nanoparticles is presented using multiple material characterization techniques. It was found that the two systems show different capping mechanism and hence differ in their intrinsic core and surface properties. The compound BINAP plays only surface capping agent and stabilizes the gold nanoparticles, resulting in small particle size and suppressed surface plasmon resonance absorption at 520 nm. The DABN capping ligand is different from BINAP and acts as both reducing and capping agent, causing the reduction of Au (III) to Au (0). The nucleation growth of the gold core occurs in accordance with the polymerization-passivation process by DABN, resulting in a big particle size of 20 nm. A strong surface plasmon resonance band shows a maximum peak at 564 nm, consistent with the Au core size. The simultaneous oxidative polymerization of DABN and the induced metal reduction process lead to the formation of gold nanoparticles encapsulated by a mixture of DABN oligomers or polymers.