Jun Matsui

Spatiotemporal photomodulation of ion (proton) transport is a key issue in creating functional ion‐based applications, ranging from energy systems to emerging neuromorphic devices. In this paper, we demonstrate reversible and stable photomodulation of proton transport. Proton‐conducting side‐chain liquid crystalline (SCLC) copolymers with varying sulfonic acid contents are synthesized via free‐radical copolymerization. The LC nature of the copolymers is investigated by polarized optical microscopy, differential scanning calorimetry, and X‐ray scattering (XRS) measurements. Ultraviolet (UV)–visible absorption spectroscopy and grazing‐incidence XRS measurements reveal that the SCLC copolymers form hetero‐lamellar structures formed by nanosegregation of hydrophobic liquid crystalline azobenzene (Az) side chains and hydrophilic sulfonic acid side chains along the polymer main chain. Moreover, we reveal that the sulfonic acid nanochannels serve as proton‐conducting pathways. Proton conductivity of the copolymer thin films is evaluated by impedance spectroscopy under controlled temperature and relative humidity conditions. These results demonstrate stable and reversible photoswitching of proton conductivity by approximately two orders of magnitude, attributed to the trans – cis photoisomerization of Az side chains under UV light irradiation. These findings open up opportunities for applications in ion (proton)‐based photofunctional neuromorphic devices.

Humidity annealing drives π-conjugated anion-containing P4VCxP+ to form ordered hexagonal ionic microstructures via self-assembly and intermolecular interactions.

In this study, an intrinsic ion–electron (hole) coequally conductive state is introduced, induced by de‐doping in self‐doped poly(3,4‐ethylenedioxythiophene) (S‐PEDOT) nanofilms, enhances the performance of in‐material physical reservoirs (PRs) through the cooperative utilization of both carriers. A chemical dedoping modulates the electrical characteristics of the S‐PEDOT PRs. Impedance spectroscopy under controlled relative humidity (RH) conditions reveals that the predominant conducting carriers of the S‐PEDOT nanofilms change systematically depending on the RH. Under low RH, the dominant carriers are holes. At a moderate RH (60–80%), the S‐PEDOT nanofilm exhibits a hole–proton mixed conducting state. A further increase in RH leads to predominantly proton carrier conduction. Moreover, the PR performance of the S‐PEDOT nanofilms is evaluated by wave generation and nonlinear autoregressive moving average (NARMA) tasks. The S‐PEDOT PRs display the best performance at RHs ranging from 60% to 80% (mixed conducting state). Therefore, it is concluded that this high PR performance is attributed to the complex dynamics originating from the cooperative hole–proton mixed conducting state of the S‐PEDOT nanofilms. The results obtain in the present study are the first report of PRs using intrinsically ion–electron mixed conducting states, paving the way for the development of high‐performance material‐based PRs.

To realize the formation and transfer of triplet excited states in hybrid organic-inorganic materials, material designs that facilitate efficient triplet sensitization and suppress molecular excited-state deactivation are imperative. In this study, we demonstrated the efficient formation of molecular triplet excited states via through-space triplet energy transfer (TET) in a perovskite nanocrystal (PNC)─pyrene (Py)─composite film. Uniform dispersion of Py as an organic acceptor within the PNC matrix facilitated effective TET, enabling room-temperature Py phosphorescence emission with an average lifetime of 60.7 ms. The TET process exhibited an efficiency of 22%, and the oxygen barrier properties of the PNC matrix suppressed oxygen quenching, allowing retention of Py phosphorescence even under ambient conditions. The proposed simple and effective material design strategy for extending the functionalities of organic acceptor molecules through controlled interface interactions can be applied in triplet-triplet annihilation upconversion and photocatalysis.

This study demonstrates that a simple statistical copolymer thin film readily forms a lamellar structure with sub-10 nm periodicity oriented perpendicular to the substrate by annealing in water.

In this study, π-conjugated anions were employed as counterions in poly(4-vinyl-N-alkylpyridinium) (P4VCxP⁺) polymers to construct highly ordered ionic microstructures. NMR, FT-IR, UV-vis spectroscopy, and differential scanning calorimetry were employed to characterize the resulting ion-pair polymers. Furthermore, thin films were fabricated and subjected to humidity annealing above the glass transition temperature. Grazing-incidence small-angle X-ray scattering (GI-SAXS) showed that humidity annealing promoted the formation of hexagonally packed cylindrical microdomains in P4VCxP⁺ with π-conjugated anion. The π-conjugated anions increased the effective hydrophilic volume and facilitated structural alignment via π–π and dipole–dipole interactions. Optical absorption analysis indicated that both the pyridinium and π-conjugated anions exhibited edge-on orientations and revealed the dynamic behavior of TCNQ·–, including dimerization and charge-transfer complex formation. Thus, π-conjugated ion pairs show significant promise for controlled self-assembly and functional optical properties in polymeric materials.

To realize the formation and transfer of triplet excited states in hybrid organic–inorganic materials, material designs that facilitate efficient triplet sensitization and suppress molecular excited state deactivation are imperative. In this study, we demonstrated the efficient formation of molecular triplet excited states via through-space triplet energy transfer (TET) in a perovskite nanocrystal (PNC)—pyrene (Py)—composite film. Uniform dispersion of Py as an organic acceptor within the PNC matrix facilitated effective TET, enabling room-temperature Py phosphorescence emission with an average lifetime (44.7 ms). The TET process exhibited an efficiency of 22%, and the oxygen barrier properties of the PNC matrix suppressed oxygen quenching, allowing retention of Py phosphorescence even under ambient conditions. The proposed simple and effective material design strategy for extending the functionalities of organic acceptor molecules through controlled interface interactions can be applied in triplet–triplet annihilation upconversion and photocatalysis.

Proton conductive polymers are one of the basic materials for polymer electrolyte membranes (PEMs) in polymer electrolyte fuel cells (PEFCs). Currently, perfluorosulfonic acid polymers (PFSAs), such as Nafion, are commonly used as PEMs due to their high proton conductivity. However, PFSA is a material with a high environmental impact. Cellulose nanofibers (CNFs) are a promising new membrane material for PEMs, with a much lower environmental impact compared to current PFSA-based PEMs. In this study, we fabricated a PEM with high proton conductivity using a phosphoric acid substituted CNF (P-CNF). P-CNFs with different amounts of phosphoric groups were synthesized by phosphorylation of hydroxy groups on CNFs and their membranes were prepared by the casting method. The SEM images showed that P-CNFs were closely packed and aligned their long axis parallel to the membrane plane. The P-CNF membrane demonstrated a maximum proton conductivity of 1.2 × 10⁻¹ S cm⁻¹ due to its high ion exchange capacity of 3.40 mmol g⁻¹ and the formation of a continuous proton conductive channel by the fiber surface inside the membrane. The high ion exchange capacity is achieved without sacrificing the mechanical strength of the membrane by modifying it with phosphoric acid, which is a moderate acid. The proton conductivity of the P-CNF membrane was equivalent to that of Nafion 212, measured at 20–80 °C and 95% RH. The results suggest that P-CNF membranes have high potential as environmentally sustainable alternative PFSA-based PEMs.

Spatiotemporal control of ion conductivity is a key issue for creating emerging fields of functional ion‐conducting nanomaterials. In the present paper, we demonstrate the formation of hetero‐smectic lamellar structures, which are formed by nanosegregation of hydrophobic liquid crystalline (LC) azobenzene side chains and hydrophilic acrylic acid side chains via polymer main chains in side‐chain LC (SCLC) copolymers, and the reversible photoswitching of the proton conductivity. Proton‐conducting SCLC copolymers with different acrylic acid contents are synthesized by free‐radical copolymerization. The LC nature of the synthesized polymers is investigated by polarized optical microscope observation, differential scanning calorimetry and X‐ray scattering measurements. Ultraviolet (UV)–visible absorption spectroscopy and grazing incidence X‐ray scattering measurements reveal the hetero‐smectic lamellar formation of SCLC copolymer thin films. Proton conductivity of the polymer thin films is evaluated by impedance spectroscopy measurements under different temperatures and relative humidity conditions with sequential UV light irradiation. These results indicate that stable and reversible photoswitching of the proton conductivity around one order of magnitude is attributed to the trans–cis photoisomerization of azobenzene side chains by UV light irradiation. These results offer the opportunity for applications of photo‐functional nanomaterials including emerging biomimetic ionic signal transduction devices and neuromorphic devices. © 2024 Society of Chemical Industry.