Concluding remarks: challenges and prospects in organic photonics and electronics.

The Faraday Discussion meeting on 'challenges and prospects in organic and photonics and electronics' was held in Osaka, Japan, after the COVID pandemic and during the subsequent global difficulties, in the traditional face-to-face and condensed style, with many discussions, both after the short presentations and in front of the poster presentations. I would like to take this opportunity to thank the organising members, particularly Youhei Takeda and local professors, for their efforts in organising this meeting.

Two States of Water Converge to One State below 215 K.

Anomalies of water have been explained by the two-state water model. In the model, water becomes one state upon supercooling. However, water crystallizes completely below 235 K ("no man's land"). The structural origin of the anomalous of the water is hidden in the "no man's land". To understand the properties of water, the spectroscopic experiment in "Norman's land" is inevitable. Hence, we proposed a new soft-confinement method for standard nuclear magnetic resonance spectroscopy to explore the "no man's land". We found the singularity temperature (215 K) at ambient pressure. Water exists in one state below 215 K. Above 215 K, the two states of water are supercritical states of the liquid-liquid critical point. The current study provides a perspective to determine the liquid-liquid critical point of water existing in a high-pressure condition.

Copolymer of Phenylene and Thiophene toward a Visible-Light-Driven Photocatalytic Oxygen Reduction to Hydrogen Peroxide.

π-Conjugated polymers including polythiophenes are emerging as promising electrode materials for (photo)electrochemical reactions, such as water reduction to H2 production and oxygen (O2) reduction to hydrogen peroxide (H2O2) production. In the current work, a copolymer of phenylene and thiophene is designed, where the phenylene ring lowers the highest occupied molecular orbital level of the polymer of visible-light-harvesting thiophene entities and works as a robust catalytic site for the O2 reduction to H2O2 production. The very high onset potential of the copolymer for O2 reduction (+1.53 V vs RHE, pH 12) allows a H2O2 production setup with a traditional water-oxidation catalyst, manganese oxide (MnO x ), as the anode. MnO x is deposited on one face of a conducting plate, and visible-light illumination of the copolymer layer formed on the other face aids steady O2 reduction to H2O2 with no bias assistance and a complete photocatalytic conversion rate of 14 000 mg (H2O2) gphotocat -1 h-1 or ≈0.2 mg (H2O2) cm-2 h-1.

Nonpolar Water Clusters: Proton Nuclear Magnetic Resonance Spectroscopic Evidence for Transformation from Polar Water to Nonpolar Water Clusters in Liquid State.

The hydrophilic/hydrophobic interactions of water are important in biological and chemical self-assembly phenomena. Water clusters in hydrophobic environments exhibit a unique morphology. Their process of formation and nonpolar properties have been extensively studied, but no direct experimental evidence has been available until now. This study provides spectroscopic evidence for the transformation of water to nonpolar configuration via clustering. Although individual water molecules form hydrogen bonds with the hydroxyl protons of n-hexanol when codissolved in a nonpolar solvent (toluene-d8), the water clusters are comprised solely of hydrogen bonds between water molecules and do not form hydrogen bonds with the hydroxyl protons of n-hexanol. This behavior indicates that the water clusters are nonpolar rather than polar. This study reports the first example of nonpolar water configuration produced via a liquid-state clustering. This property is a common and important interfacial phenomenon of water in chemistry, biology, materials science, geology, and meteorology.

Optimizing the Interdomain Spacing in Alicyclic Polythiourea toward High-Energy-Storable Dielectric Material.

Organic dielectric materials have been widely developed and investigated for energy storage capacitors. However, challenges remain in terms of the relatively low dielectric constant and energy density. Enhancing the dipolar polarization to increase the dielectric constant is considered to be an effective way to improve the energy density of polymer dielectrics. Herein, enlightened by the chain-packing structure that affects the dipolar relaxation behavior, a simple and low-cost approach is proposed to tailor the interdomain spacing in an alicyclic polythiourea (PTU) by changing quenching temperatures and further facilitate the dipolar polarization. It is found that the large interdomain spacing is beneficial to promote the localized motion of segmental chains in amorphous regions, but at the same time inevitably reduces the dipole density. Therefore, in order to achieve the highest dielectric constant in the PTU, there is an optimal value for the interdomain spacing. It is worth noting that the dielectric constant of PTU increases from 5.7 to 10, and thus the energy density increases by 53% to 16.3 J cm-3 . It proposes a simple and feasible strategy to further improve the energy density through optimizing the interdomain spacing toward high-energy-storable dielectric material.

Supercooled Low-Entropy Water Clusters.

The properties of low-entropy water clusters and small bulk water domains in a hydrophobic solvent over a wide temperature range (235-333 K), including supercooling temperatures, were investigated. 1H nuclear magnetic resonance spectroscopy showed singularity temperatures at ∼300, 250, 235, and 225 K. We proposed a model to understand these singularity temperatures in which the low-entropy water cluster is a locally favored tetrahedral structure (LFTS) and the small bulk water domain contains a mixture of disordered normal-liquid structure (DNLS) and LFTS. The model showed that the LFTS and DNLS populations change with applied temperature. Above ∼300 K, all local water structures become a DNLS. The population of LFTS increases with cooling and becomes dominant below ∼250 K. At ∼225 K, all local water structures converge to LFTS. The phase-transition rate of the low-entropy water clusters and small bulk water domains increases significantly at ∼235 K. The phase transition of the low-entropy water clusters showed primary ice nucleation. Low-entropy water clusters in a hydrophobic solvent are a unique water morphology and a probe material for water investigations.

Conducting Redox Polymer as a Robust Organic Electrode-Active Material in Acidic Aqueous Electrolyte towards Polymer-Air Secondary Batteries.

Organic materials receive increasing attention as environmentally benign and sustainable electrode-active materials. We present a conducting redox polymer (CRP) based on poly(3,4-ethylenedioxythiophene) with naphthoquinone pendant group, which is formed from a stable suspension of a trimeric precursor and an oxoammonium cation as oxidant. This suspension allows us to easily coat the polymer onto a current collector, opening up use of roll-to-roll processing or ink-jet printing for electrode preparation. The CRP showed a full capacity of 76 mAh g-1 even at a high C rate of 100 C in acidic aqueous electrolyte. These properties make the CRP a promising candidate as anode-active material; a polymer-air secondary battery was fabricated with the CRP as anode, a conventional Pt/C catalyst as cathode, and sulfuric acid aqueous solution as electrolyte. This battery yielded a discharge voltage of 0.50 V and showed good cycling stability with 97 % capacity retention after 100 cycles and high rate capabilities up to 20 C.

Poly(dihydroxybenzoquinone): its high-density and robust charge storage capability in rechargeable acidic polymer-air batteries.

A rechargeable acidic polymer-air battery was firstly fabricated with poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) as the anode, the conventional Pt/C cathode catalyst, and acidic aqueous electrolyte (pH 1). This battery yielded a high discharging capacity of 349 mA h gpolymer-1 with a long-lifetime of >500 cycles and high rate capabilities (up to 10C).

Vapor-Phase Formation of a Hole-Transporting Thiophene Polymer Layer for Evaporated Perovskite Solar Cells.

Homogeneous layer formation on textured silicon substrates is essential for the fabrication of highly efficient monolithic perovskite silicon tandem solar cells. From all well-known techniques for the fabrication of perovskite solar cells (PSCs), the evaporation method offers the highest degree of freedom for layer-by-layer deposition independent of the substrate's roughness or texturing. Hole-transporting polymers with high hole mobility and structural stability have been used as effective hole-transporting materials (HTMs) of PSCs. However, the strong intermolecular interactions of the polymers do not allow for a layer formation via the evaporation method, which is a big challenge for the perovskite community. Herein, we first applied a hole-transporting terthiophene polymer (PTTh) as an HTM for evaporated PSCs via an in situ vapor-phase polymerization using iodine (I2) as a sublimable oxidative agent. PTTh showed high hole mobility of 1.2 × 10-3 cm2/(V s) and appropriate energy levels as HTM in PSCs (EHOMO = -5.3 eV and ELUMO = -3.3 eV). The PSCs with the in situ vapor-phase polymerized PTTh hole-transporting layer and a co-evaporated perovskite layer exhibited a photovoltaic conversion efficiency of 5.9%, as a proof of concept, and high cell stability over time. Additionally, the polymer layer could fully cover the pyramidal structure of textured silicon substrates and was identified as an effective hole-transporting material for perovskite silicon tandem solar cells by optical simulation.

Ultrahigh oxygen-scavenging norbornene copolymers bearing imidazolyl iron complexes for fabricating active and sustainable packaging films.

A tough and transparent norbornene copolymer film affixing an imidazolyl iron-salen complex catalyst exhibited an ultra-high, humidity-independent, and monthly paced oxygen-scavenging capacity up to 300 mL (oxygen gas at STP)/g(film). The homogeneously dispersed and immobilized iron complex in the polymer matrix catalytically contributed to the exceptionally high-yield oxidative consumption of polymer allylic bonds.

Anti-Oxidizing Radical Polymer-Incorporated Perovskite Layers and their Photovoltaic Characteristics in Solar Cells.

A small amount of a radical-bearing redox-active polymer, poly(1-oxy-2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMA), incorporated into the photovoltaic organo-lead halide perovskite layer significantly enhanced durability of both the perovskite layer and its solar cell and even exposure to ambient air or oxygen. PTMA acted as an eliminating agent of the superoxide anion radical formed upon light irradiation on the layer, which can react with the perovskite compound and decompose it to lead halide. A cell fabricated with a PTMA-incorporated perovskite layer and a hole-transporting polytriarylamine layer gave a photovoltaic conversion efficiency of 18.8 % (18.2 % for the control without PTMA). The photovoltaic current was not reduced in the presence of PTMA in the perovskite layer probably owing to a carrier conductivity of PTMA. The incorporated PTMA also worked as a water-repelling coating for providing humidity-resistance to the organo-lead halide perovskite layer.

Fibrous Materials Made of Poly(ε-caprolactone)/Poly(ethylene oxide)-b-Poly(ε-caprolactone) Blends Support Neural Stem Cells Differentiation.

In this work, we design and produce micron-sized fiber mats by blending poly(ε-caprolactone) (PCL) with small amounts of block copolymers poly(ethylene oxide)m-block-poly(ε-caprolactone)n (PEOm-b-PCLn) using electrospinning. Three different PEOm-b-PCLn block copolymers, with different molecular weights of PEO and PCL, were synthesized by ring opening polymerization of ε-caprolactone using PEO as initiator and stannous octoate as catalyst. The polymer blends were prepared by homogenous solvent mixing using dichloromethane for further electrospinning procedures. After electrospinning, it was found that the addition to PCL of the different block copolymers produced micron-fibers with smaller width, equal or higher hydrophilicity, lower Young modulus, and rougher surfaces, as compared with micron-fibers obtained only with PCL. Neural stem progenitor cells (NSPC), isolated from rat brains and grown as neurospheres, were cultured on the fibrous materials. Immunofluorescence assays showed that the NSPC are able to survive and even differentiate into astrocytes and neurons on the synthetic fibrous materials without any growth factor and using the fibers as guidance. Disassembling of the cells from the NSPC and acquisition of cell specific molecular markers and morphology progressed faster in the presence of the block copolymers, which suggests the role of the hydrophilic character and porous topology of the fiber mats.

A New Methodology to Create Polymeric Nanocarriers Containing Hydrophilic Low Molecular-Weight Drugs: A Green Strategy Providing a Very High Drug Loading.

To date, a large number of active molecules are hydrophilic and aromatic low molecular-weight drugs (HALMD). Unfortunately, the low capacity of these molecules to interact with excipients and the fast release when a formulation containing them is exposed to biological media jeopardize the elaboration of drug delivery systems by using noncovalent interactions. In this work, a new, green, and highly efficient methodology to noncovalently attach HALMD to hydrophilic aromatic polymers to create nanocarriers is presented. The proposed method is simple and consists in mixing an aqueous solution containing HALMD (model drugs: imipramine, amitriptyline, or cyclobenzaprine) with another aqueous solution containing the aromatic polymer [model polymer: poly(sodium 4-styrenesulfonate) (PSS)]. NMR experiments demonstrate strong chemical shifting of HALMD aromatic rings when interacting with PSS, evidencing aromatic-aromatic interactions. Ion pair formation and aggregation produce the collapse of the system in the form of nanoparticles. The obtained nanocarriers are spheroidal, their size ranging between 120 and 170 nm, and possess low polydispersity (≤0.2) and negative zeta potential (from -60 to -80 mV); conversely, the absence of the aromatic group in the polymer does not allow the formation of nanostructures. Importantly, in addition to high drug association efficiencies (≥90%), the formed nanocarriers show drug loading values never evidenced for other systems comprising HALMD, reaching ≈50%. Diafiltration and stopped flow experiments evidenced kinetic drug entrapment governed by molecular rearrangements. Importantly, the nanocarriers are stable in suspension for at least 18 days and are also stable when exposed to different high ionic strength, pH, and temperature values. Finally, they are transformable to a reconstitutable dry powder without losing their original characteristics. Considering the large quantity of HALMD with importance in therapeutics and the simplicity of the presented strategy, we envisage these results as the basis to elaborate a number of drug delivery systems with applications in different pathologies.

Reversible Hydrogen Releasing and Fixing with Poly(Vinylfluorenol) through a Mild Ir-Catalyzed Dehydrogenation and Electrochemical Hydrogenation.

The radical polymerization of 2-vinylfluorenol, an alcohol derivative of vinylfluorene, gives poly(vinylfluorenol), which quantitatively releases hydrogen gas (≈110 mL per gram polymer at standard temperature and pressure) by simply warming at 100 °C with an iridium catalyst. A high population of fluorenol units in the polymer accomplishes a large formula-weight-based theoretical hydrogen density (1.0 wt%). The dehydrogenated ketone derivative, poly(vinylfluorenone), exhibits reversible negative-charge storage with a high density of 260 mAh g-1 . The electrolytically reduced poly(vinylfluorenone) is momentarily hydrogenated in the presence of an electrolyte with water as the hydrogen source to be converted to the original poly(vinylfluorenol). The formed poly(vinylfluorenol) almost quantitatively evolves hydrogen gas similar to the starting poly(vinylfluorenol). Both hydrogen and charge storage with the organic fluorenol/fluorenone polymer suggest a new type of energy-storage configuration.

Ultrathin and Stretchable Rechargeable Devices with Organic Polymer Nanosheets Conformable to Skin Surface.

Ultrathin flexible electronic devices have been attracting substantial attention for biomonitoring, display, wireless communication, and many other ubiquitous applications. In this article, organic robust redox-active polymer/carbon nanotube hybrid nanosheets with thickness of just 100 nm are reported as power sources for ultrathin devices conformable to skin. Regardless of the extreme thinness of the electrodes, a moderately large current density of 0.4 mA cm-2 is achieved due to the high output of the polymers (>10 A g-1 ). For the first time, the use of mechanically robust yet intrinsically soft electrodes and polymer nanosheet sealing leads to the fabrication of rechargeable devices with only 1-µm thickness and even with stretchable properties.

Long-lived water clusters in hydrophobic solvents investigated by standard NMR techniques.

Unusual physical characteristics of water can be easier explained and understood if properties of water clusters are revealed. Experimental investigation of water clusters has been reported by highly specialized equipment and/or harsh experimental conditions and has not determined the properties and the formation processes. In the current work, we used standard 1H-NMR as a versatile and facile tool to quantitatively investigate water clusters in the liquid phase under ambient conditions. This approach allows collection of data regarding the formation, long lifetime, stability, and physical properties of water clusters, as a cubic octamer in the liquid phase.