Synthesis of novel stable nanometer-sized metal (M = Pd, Au, Pt) colloids protected by a π-conjugated polymer

Novel pi-conjugated polymer-protected metal (M = Pd, Au, Pt) nanoparticles of narrow size distribution and high dispersity were prepared via reduction of the metal ions by a pi-conjugated poly(dithiafulvene) (PDF) having strong electron-donating properties. The oxidized polymer protected the metal nanoparticles as stable colloidal forms without any precipitation for more than a month at room temperature under air. Due to the effect of the positively charged PDF, the absorption spectrum of the protected gold nanoparticle assigned to the surface plasmon resonance was found to display a strong red shift. The absorption band of the oxidized PDF assigned to the pi-pi* transition also showed a strong red shift compared with that of the pure PDF due to the effective expansion of T-conjugation of the oxidized PDF by charge transfer. The influences of the reaction temperature and PDF concentration were investigated on the metal nanoparticle size with the Pt nanoparticle as an example. The protected metal nanoparticles were characterized using transmission electron microscopy, the UV-vis absorption spectrum, and X-ray diffraction. The redox behavior of the metal nanoparticle dispersed pi-conjugated PDF was elucidated with cyclic voltammetry measurement.