Facile preparation of gold nanoparticle with diarylethene polymers by disodium malate and its photoreversible optical properties

We have developed a synthetic procedure of gold nanoparticle covered with polystyrene (Au-poly(St)) using organic acid salts, followed by a ligand exchange reaction. First, various chain lengths of polystyrenes (poly(St)s) bearing thiol-end group were used as the covering agent of gold nanoparticle prepared by reduction using trisodium citrate. The resulting nanoparticles with ca. 13 nm diameter were dispersed in toluene when the molecular weight of the ligand poly(St) is larger than 1200. Larger sized Au-poly(St) could be obtained using disodium malate instead of the citrate. The colloidal gold nanoparticle with ca. 40 nm diameter was easily prepared only by changing the reducing agent. Finally, we have demonstrated to prepare larger sized gold nanoparticle covered with a photochromic diarylethene polymer (Au-poly(DE)) that shows large change in local surface plasmon resonance absorption according to the photochromic reaction even in a solution.