Ryohei Yasukuni

Photoswitchable interactions between photochromic organic diarylethene and surface plasmon resonance of gold nanoparticles in hybrid thin films

Hybrid materials combining gold nanoparticles (GNP) of variable diameter and an organic thin layer of photochromic diarylethenes were achieved. Solid-state photoswitching based on ring-closure/ring-opening reaction was carried out under alternate UV and visible irradiations. In addition to the spectral changes due to the photochromism itself, the surface plasmon resonance related to the GNP is significantly modified, influenced by a photoinduced change in the refractive index of its environment. These two contributions were sorted out, showing the possibility of probing a photochromic switch by following the plasmon band. The shape change of the plasmon band was consistently compared to calculations based on the Mie theory. Additionally, with one given diarylethene compound, both UV-visible spectroscopy and surface enhanced Raman scattering (SERS) spectroscopy showed an acceleration of the ring-opening photochromic reaction in the presence of GNP.

Size-Dependent Optical Properties of Dendronized Perylenediimide Nanoparticle Prepared by Laser Ablation in Water

Fluorescent nanoparticles of dendronized perylenediimide (DPDI) were fabricated by laser ablation in water. We succeeded in the preparation of colloidal nanoparticles of different sizes (150–400 nm) and examined their size-dependent optical absorption and fluorescence properties. The size-dependent extinction spectra can be explained by the effect of light scattering loss, and it was confirmed that their absorption spectrum is similar to that of molecules in solution. The very weak interchromophoric interaction is also confirmed by fluorescence spectral measurement. On the other hand, we found that the fluorescence quantum yield decreases with decreasing of the particle size, and we propose a new mechanism for the size-dependent reduction of emission intensity in organic nanoparticles. On the basis of the size dependent-fluorescence quantum yield and solvent polarity dependence of DPDI fluorescence in organic solvents, we considered that, while the interchromophoric interactions are weak in the nanoparticle, the excited singlet state migrates in a nanoparticle owing to energy hopping and is quenched at the surface, leading to the observed size-dependent fluorescence quantum yield (Φf) and a smaller value of Φf for nanoparticles than for the molecules in nonpolar solvents.

Pulsed-laser-activated impulse response encoder: Sensitive detection of surface elastic waves on biomimetic microsized gel spheres

A femtosecond-laser-induced impulsive force was applied to microsized calcium alginate (CaAlg) gel spheres as an external force to excite elastic waves. To evaluate elasticity, atomic force microscopy (AFM) was applied to detect vibration propagation. The sphere size dependence of the vibration was well reproduced by finite element method (FEM) simulation for pressure waves and surface acoustic waves. The obtained results indicate that the pulsed-laser-activated impulse response encoder (PLAIRE) enables the sensitive detection of elasticities, not only on inside but also on the surface.