Shinji Kajimoto

Picosecond and nanosecond photo-dynamics of a naphthopyran merocyanine

For the first time the photochemistry of the trans, trans (TT) to trans, cis (TC) isomerisation for merocyanines (MCs) of a chromene (CHR) compound has been investigated using steady-state nanosecond and time-resolved femtosecond irradiation. The dominant photo-transformation of the TT isomer by these irradiations is conversion to TC. The yield of the TT to TC photoreaction is inherently low in all solvents studied due to efficient ground state recovery in competition with inter-system crossing, but it is lowest of all in polar solvents. Several intermediate states have been identified in the first 6 ns of the reaction that we tentatively assigned, including a possible twisted MC T1 state. We assign other distinct states to TT S1, TT T1 and a further species to TC T1. The full photochemical conversion from TT to TC is a slower process than 6 ns. The presence of oxygen marginally increases the overall bleaching of the TT isomer and slightly enhances TC formation.

Explosive boiling of water after pulsed IR laser heating

By focussing 1 J of 1064 nm Nd ∶ YAG beam into 30 atmospheres of hydrogen we could Raman shift to produce a 10 ns, 300 mJ, 1.9 µm laser pulse. This pulse can directly heat water by more than 100 K (average), during the laser pulse, inducing vaporisation. Vaporisation was studied using time-resolved shadowgraphy and Raman spectroscopy to obtain macro and molecular level information. The O–H stretching Raman bands of water are sensitive to temperature allowing us to measure the average temperatures during the boiling process. After the T-jump, explosive boiling occurred within 100 ns during which time the bulk temperature decreased, indicating that the vaporising water molecules deprived heat from their surroundings. Shadowgraphs confirmed the timescale for this phenomenon visually. After 10 µs, vaporised gas molecules condensed and formed droplets, which were observed by a morphology-dependent resonance (MDR) Raman.

Additive-free size-controlled synthesis of gold square nanoplates using photochemical reaction in dynamic phase-separating media.

Ultrafast phase separation of water and 2-butoxyethanol mixture was induced by nanosecond IR laser pulse irradiation. After a certain delay time, a UV laser pulse was introduced to induce photoreduction of aurate ions, which led to the formation of gold nanoparticles in dynamic phase-separating media. The structure and size of the nanoparticles varied depending on the delay time between the IR and UV pulses. For a delay time of 5 and 6 μs, gold square plates having edge lengths of 150 and 100 nm were selectively obtained, respectively. With a delay time of 3 μs, on the other hand, the size of the square plates varied widely from 100 nm to a few micrometers. The size of the gold square plates was also varied by varying the total irradiation time of the IR and UV pulses. The size distribution of the square plates obtained under different conditions suggests that the growth process of the square plates was affected by the size of the nanophases during phase separation. Electron diffraction patterns of the synthesized square plates showed that the square plates were highly crystalline with a Au(100) surface. These results showed that the nanophases formed during laser-induced phase separation can provide detergent-free reaction fields for size-controlled nanomaterial synthesis.

Doping concentration dependence on VUV luminescence of Tm:CaF2

We are developing a new photon detector with gas amplification devices. We combined the CsI photocathode with GEM/uPIC for the first prototype which is aimed at the application to the large liquid Xe detectors. We assembled 10cm×10cm μPIC+GEMs and a 5cmφ MgF2 window with a transmissive CsI photocathode into a prototype detector. Using Ar+10%C2H6 gas, we achieved the gas gain of 105 which is enough to detect single photoelectron. We, then, irradiate UV photons with the Excimer Xe lamp to the prototype detector and we successfully detected the UV photons.

Surface Structuring Using Photo-Polymerization at the Interface between Vinyl-Modified Quartz and a Dynamic Phase Separating Solution

Spinodal phase separation was initiated using a nanosecond infrared laser temperature-jump at the interface between a modified quartz surface and a 2-butoxyethanol-water solution. The evolving phase domains formed spatial distributions of solvents and solutes at the interface. Radical photo-polymerization was induced in this solution using pulsed UV laser irradiation. Various polymer patterns formed at the quartz surface, depending on the UV pulse delay time after the initiation of phase separation, the fluence, and the number of pulses. Patterns which formed at earlier delay times were smaller and more spatially regular than those which formed later.

Observation of Unusual Molecular Diffusion Behaviour below the Lower Critical Solution Temperature of Water/2-Butoxyethanol Mixtures by using Fluorescence Correlation Spectroscopy

The effect of solute affinity on solute diffusion in binary liquids well below the lower critical solution temperature (LCST) was studied by using fluorescence correlation spectroscopy. We measured the hydrodynamic radii of a hydrophobic and an amphiphilic fluorescent dye under systematic variation of the relative molar fractions of water/2-butoxyethanol and, for comparison, of water/methanol mixtures, which do not show phase separation. We found that the apparent hydrodynamic radius of the hydrophobic dye almost doubled in water/2-butoxyethanol, whereas it remained largely unchanged for the amphiphilic dye and in water/methanol mixtures. Our results indicate that the translational diffusion of solutes is influenced by transient local solution structures, even at temperatures well below the LCST. We conclude that, even far below LCST, different solutes can experience different environments in binary liquid mixtures depending on both the solute and solvent properties, all of which impact their reactivity.

Dynamics of Volume Expansion of De-Mixing Liquids after Pulsed IR Heating

Triethylamine (TEA)–water mixtures have a critical-temperature (Tc). Below Tc the mixture exists as one phase and above Tc it exists in two phases. The de-mixed volume is different to the mixed volume. A nanosecond pulsed-laser heated a TEA–water mixture so that it de-mixed. The resulting dynamics of volume expansion were monitored using interferometry. For T-jumps within the one phase region the dynamics of volume change were limited by the speed of sound. However, T-jumps between the one and two phase regions also manifested a slower volume change associated with the de-mixing process. After 150 ns, the volume of the de-mixed TEA–water was consistent with the equilibrium volume change. This suggests that, within 150 ns, the system had split into phase-domains having equilibrium compositions of TEA and water. Subsequently the phase domains would simply merge and grow resulting in no further volume change to reduce surface tension between the phases.

Picosecond dynamics of hydrogen bond rearrangements during phase separation of a triethylamine and water mixture

The earliest stages of phase separation in a liquid triethylamine (TEA)-water mixture were observed using a picosecond IR laser pulse to produce a temperature jump and ultrafast Raman spectroscopy. Raman spectral changes in the water OH stretching region showed that the temperature rise induced by IR pulses equilibrated within a few tens of picoseconds. Amplitude changes in the TEA CH-stretching region of difference Raman spectra consisted of an initial faster and a subsequent slower process. The faster process within 100 ps is attributed to hydrogen bond weakening caused by the temperature rise. The slower process attributed to phase separation was observed for several nanoseconds, showing the number of hydrogen bond between TEA and water gradually decreased with time. The kinetics of hydrogen bond scission during phase separation indicated a linear growth of the phase-separated component, as observed previously on the nanosecond time scale, rather than the more usual exponential growth. A peak blueshift was observed in the difference Raman spectra during phase separation. This shift implies that hydrogen bond scission of TEA-water aggregates involving very few water molecules took place in the initial stage of phase separation (up to 2 ns), and then was followed by the breaking of TEA-water pairs surrounded by water molecules. This effect may be a result from spatial inhomogeneities associated with the phase separation process: aggregates or clusters existing naturally in solution even below the lower critical soluble temperature.

VUV Luminescence With Nd Doped KCaF

Radioluminescence properties of Nd doped KCaF3 single crystals were studied. X-ray excited luminescence spectra were measured in the vacuum ultraviolet (VUV) region by using a custom-made device filled with nitrogen atmosphere. As a result, VUV luminescence was observed at 190 nm. Radioluminescence intensity due to the core-valence luminescence (CVL) of KCaF3 decreased with increasing of Nd3+ concentration.

_{3}

We report direct observation of a spatial distribution of water molecules inside of a living cell using Raman images of the O-H stretching band of water. The O-H Raman intensity of the nucleus was higher than that of the cytoplasm, indicating that the water density is higher in the nucleus than that in the cytoplasm. The shape of the O-H stretching band of the nucleus differed from that of the cytoplasm but was similar to that of the balanced salt solution surrounding cells, indicating less crowded environments in the nucleus. The concentration of biomolecules having C-H bonds was also estimated to be lower in the nucleus than that in the cytoplasm. These results indicate that the nucleus is less crowded with biomolecules than the cytoplasm.