Fe(phen)2(NCS)2] is a prototype transition metal complex material, which undergoes a phase transition between low-spin (LS) and high-spin (HS) phases, induced by temperature, pressure or light. Vibrational modes play a key role for spin-state switching both in thermal and photo-induced cases, by contributing to vibrational entropy for thermal equilibrium transitions or driving the fast structural trapping of the photoinduced high spin state.Here we study the crystal phonon modes of [Fe(phen)2(NCS)2], by combining THz, IR, and Raman spectroscopies sensitive to modes in different frequency ranges and different symmetries. We compare the experimental results to DFT calculations performed in a periodic 3D crystal for understanding the phonon modes in the crystal, compared to molecular vibrations. Indeed, each vibrational mode of the isolated molecule combines into several modes of different symmetry and frequency in the crystal, as the unit cell contains four molecules. We focus our attention on the HS symmetric and anti-symmetric breathing modes in the crystal as well as on the N-CS stretching modes.

The fundamental understanding of water confined in porous coordination polymers (PCPs) is significantly important not only for their applications such as gas storage and separation, but also for exploring the confinement effects in the nanoscale spaces. Here, we report the observation of an exotic water in the well-designed hydrophilic nanopores of PCPs. Single-crystal X-ray diffraction found that nanoconfined water has an ordered structure that is characteristic in ices, but infrared spectroscopy revealed a significant number of broken hydrogen bonds that is characteristic in liquids. We found that their structural properties are quite similar to those of solidliquid supercritical water predicted in hydrophobic nanospace at extremely high pressure.Our results will open up not only new potential applications of exotic water in PCPs to control chemical reactions but also experimental systems to clarify the existence of solid-liquid critical points. Main Text:Porous coordination polymers (PCPs) or Metal-organic frameworks (MOFs) 1 have emerged as a new class of nanoporous materials constructed from organic ligands and metal ions. Compared with other porous materials, PCPs have an excellent ability to control pore structures, sizes, and surface properties, as a result of the wide variety of combinations of organic ligands and metal ions. This capability means that the nanopores of PCPs could be designed to realize an exotic state of adsorbed gas molecules not seen in the bulk phase using confinement effects 2 . Such state is interesting for molecular physics in nanospaces and also new applications to facilitate chemical reactions in nanopores of PCPs.Among gas molecules, it is known that water molecules are significantly affected by the size, geometry, and inner wall properties of the confined space. The previous studies show that confinement effects occur in spaces narrower than 100 nm scale and can be classified into two regimes. The first regime appears in spaces from 2 nm to a few tens of nanometers, where the confined water is conceptually divided into a water core with bulk liquid-like properties and a shell of water existing around the inner walls with properties

A fundamental understanding of the photoexcited carrier system in diamond is crucial to facilitate its application in photonic and electronic devices. Here, we studied the detailed balance between free carriers and excitons in pristine diamond by using a deep-ultraviolet (DUV) pump in combination with terahertz (THz) probe spectroscopy. We investigated the transformation of photoexcited carriers to excitons via an internal transition of excitons, which was newly found to occur at a frequency of approximately 15 THz. We determined the equilibrium constant in the Saha equation from the temperature dependence of the free-carrier density measured at chemical equilibrium. The derived exciton binding energy was larger than the conventional value, which indicated an energy shift due to the fine-structure splitting of the exciton states.

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