Light-Controllable Surface Plasmon Resonance Absorption of Gold Nanoparticles Covered with Photochromic Diarylethene Polymers

Various sizes of gold nanoparticles covered with photochromic diarylethene polymers (Au-poly(DE)s) were prepared by Brust's method, citrate reduction, or a seeding growth method. The diarylethene polymers oil the particles exhibited reversible photochromism upon alternating irradiation with ultraviolet and visible light, both in solution and in the solid state. Au-poly(DE) of larger size, prepared by the seeding growth method, showed a significant shift in the local surface plasmon resonance (LSPR) band photoreversibly as a result of photochromic reaction of the diarylethene polymers around the gold nanoparticles. This change is due to a change in the refractive index of the photochromic chromophore and is remarkably enhanced in the solid state, However, the smaller sized Au-poly(DE) prepared by Brust's method hardly showed my such spectral shift. These results are qualitatively reproduced by a theoretical simulation, which indicates that the sensitivity of the LSPR band strongly depends on the particle size of the gold nanoparticle. The Au-poly(DE)s can be potentially used as new types of plasmonic materials with a light-controllable LSPR band.