We have investigated the microwave response at 44.5 GHz with respect to temperature T and external magnetic field H in $\lambda -(\mathrm{BEDT}-\mathrm{TSF}{)}_2{\mathrm{FeCl}}_4$ forming a quasi two-dimensional electronic system with $\pi -d$ correlations. At 8.3 K $[{=T}_{\mathrm{MI}},$ the metal-insulator (MI) transition temperature] $<T<\mathrm{}70\mathrm{}\mathrm{K}$ ${(=T}_{\mathrm{FM}}),$ the microwave dielectric constant along the c axis, ${\epsilon }_1^c,$ takes positive large values amounting to 1000–2000. Furthermore, the microwave conductivity ${\sigma }_1^c$ starts to deviate resistively from the dc conductivity ${\sigma }_{\mathrm{dc}}^c,$ and the difference between ${\sigma }_1^c$ and ${\sigma }_{\mathrm{dc}}^c$ reaches about two orders of magnitude just above $T_{\mathrm{MI}}.$ The present results are consistent with the previous results at 16.3 GHz, and consequently the appearance of the anomalous metallic state is confirmed. An anomalous microwave response has also been observed in the $a^{*}$ and $b^{*}$ directions, and there exist large anisotropies depending sensitively on the orientations. The broad maximum of ${\epsilon }_1^c$ around 30 K is reminiscent not of a usual ferroelectric transition, but of relaxor ferroelectric behaviors. It is expected that dielectric domains or stripes with less metallic conductions emerge inhomogeneously in the $\pi$ electronic systems. Above $T_{\mathrm{FM}},$ where microwave anomalies are not present, the interplane and intraplane microwave conductivities hold anisotropies ${\sigma }_1^c/{\sigma }_1^{b^{*}}\approx {10}^3$ and ${\sigma }_1^c/{\sigma }_1^{a^{*}}\approx 10.$ In the antiferromagnetic insulating state, ${\sigma }_1^c$ becomes much conductive in comparison with ${\sigma }_{\mathrm{dc}}^c.$ Together with low frequency data, ${\epsilon }_1^c$ is found to exhibit a large frequency dispersion. The microwave response is not attributed to single particle excitations, but to some collective mode excitations associated with charge degrees of freedom. The $H-T$ phase diagram of the MI transition determined by the present microwave measurements is independent of the orientations of H, and coincides well with the phase diagram obtained by the dc magnetoresistivity and magnetization. Spin waves for the hard axis are observed as an absorption peak in the width change for the microwave magnetic field applied parallel to both H and $a^{*}.$

Collagen films with proton conduction are a candidate of next generation of fuel-cell electrolyte. To clarify a relation between proton conductivity and formation of water networks in the collagen film originating from a tilapia’s scale, we systematically measured the ac conductivity, infrared absorption spectrum, and weight change as a function of relative humidity (RH) at room temperature. The integrated absorbance concerning an O–H stretching mode of water molecules increases above 60% RH in accordance with the weight change. The dc conductivity varies in the vicinity of 60 and 83% RH. From those results, we have determined the dc conductivity vs. hydration number (N) per unit (Gly-X-Y). The proton conduction is negligible in the collagen molecule itself, but dominated by the hydration shell, the development of which is characterized with three regions. For 0 < N < 2, the conductivity is extremely small, because the water molecule in the primary hydration shell has a little hydrogen bonded with each other. For 2 < N < 4, a quasi-one-dimensional proton conduction occurs through intra-water bridges in the helix. For 4 < N, the water molecule fills the helix, and inter-water bridges are formed in between the adjacent helices, so that a proton-conducting network is extended three dimensional.

Infrared spectra at room temperature under relative humidity (RH) of 0% and 90% have been measured on dry salmon-sperm DNA incorporating various metallic ions ($M\text{-DNA}$, $M=\text{Li}$, Na, Mg, Ca, Mn, Fe, and Zn); the effects of which are examined from the molecular-vibrational points of view. Among many absorption bands, the antisymmetric and symmetric stretching modes of the phosphate group $\left({\text{PO}}_2^{-}\right)$ are found to show distinct spectral change depending on $M$. At $\text{RH}=90\%$, the band shifts appear for both modes, reflecting that the magnitude of the electric dipole of ${\text{PO}}_2^{-}$ is affected by $M$. At $\text{RH}=0\%$, a band splitting induced by the spatial anisotropy around ${\text{PO}}_2^{-}$ is detected in the antisymmetric stretching mode for Mg-DNA, Ca-DNA, Mn-DNA, Zn-DNA with divalent counterions, and Fe-DNA with trivalent counterions. The configurational change in $M$ leads to these shifts and splittings; the divalent or trivalent ions do not connect to ${\text{PO}}_2^{-}$ but are incorporated into the base-pair sequence as already pointed out by the previous measurements of NMR, ESR, and fluorescence. In $M\text{-DNA}$ with $M=\text{Mg}$, Ca, Mn, Fe, and Zn, a kink appears around $3100{\text{cm}}^{-1}$ corresponding to the NH stretching, and additionally a slight minimum disappears around $310{\text{cm}}^{-1}$. These phenomena are caused by a generation of $\text{N-}M$ stretching vibrations due to the replacement of proton in the imino group to $M$.

We studied the relationship between proton conductivity and the terahertz-regime vibrations of two-dimensional MOFs. The results of spectroscopy studies clarified the essential role played by the collective motions in the terahertz region in 2D layers for efficient H⁺ conduction. Ab initio calculations suggested the collective motion to be predominantly determined by the valence electronic structure, depending on the identity of the metal ion.

In phases III and IV of Cs₃H(SeO₄)₂, the vibrational state and intrabond transfer of the proton in the dimeric selenates are systematically studied with a wide range of absorbance spectra, a spin–lattice relaxation rate of ¹H-NMR ($T_1^{-1}$ ), and DFT calculations. The OH stretching vibrations have extremely broad absorption at around 2350 (B band) and 3050 cm⁻¹ (A band), which originate from the 0–1 and 0–2 transitions in the asymmetric double minimum potential, respectively. The anharmonic-coupling calculation makes clear that the A band couples not only to the libration but also to the OH bending band. The vibrational state (nano-second order) is observed as the response of the proton basically localized in either of the two equivalent sites. The intrabond transfer between those sites (pico-second order) yields the protonic fluctuation reflected in $T_1^{-1}$ . Together with the anomalous absorption [ν_p2 phonon, libration, tetrahedral deformation (δ₄₄₀), and 610-cm⁻¹ band], we have demonstrated that the intrabond transfer above 70 K is dominated by the thermal hopping that is collectively excited at 610 cm⁻¹ and the phonon-assisted proton tunneling (PAPT) relevant to the tetrahedral deformation [PAPT(def)]. Below 70 K, $T_1^{-1}$ is largely enhanced toward the antiferroelectric ordering and the distinct splitting emerges in the libration, which dynamically modulates the O(2)–O′(2) distance of the dimer. The PAPT(lib) associated with the libration is confirmed to be a driving force of the AF ordering.