Förster energy transfer phenomena were observed in the system of anthracene (AN) - tetracene (TE) and anthracene (AN) - perylene (PE) doped in poly-N-isopropylacrylamide (PNIPA) gel, which exhibits volume-phase transfer phenomena. In the shrunken state, the energy transfer occurred slightly. By contrast, in the swollen state, we observed that energy transfer occurred efficiently from AN to TE or PE. In general, the energy transfer process depends on the concentration and distance between the energy donor and acceptor. The actual concentration and distances between probe molecules were estimated using equations for the Förster energy transfer. The average distance changes were ca. 1 nm during swollen–shrunken processes. We were able to use Förster energy transfer phenomena for quantitative elucidation at the molecular level.

Research on aggregation-induced emission (AIE) has gained significant attention owing to its application in various fields, including bioscience. However, achieving reversible luminescence and efficient quenching in practical applications is challenging. This study aims to address these challenges by developing a material based on a poly-N-isopropylacrylamide (PNIPA) gel, a biocompatible material, incorporating tetraphenylethylene, an AIE-active molecule. The photoluminescence (PL) intensity of the gel decreased to less than 30

The production of graphite often requires temperatures as high as 3000 K and is, therefore, energy-intensive. Reducing this energy demand while maintaining material quality is essential for sustainable graphite production. Previously, we reported that energy consumption was previously reduced by ∼10% by applying a magnetic field to a part of the graphite preparation process. In this process, carbon crystallites—the building blocks of the graphite precursors—were effectively oriented during the initial stage, which enhanced crystallite interconnection during graphite formation above 1000 K. This behavior suggested that the amount of energy required for graphite preparation decreased. Herein, we aimed to accelerate the orientation of carbon crystallites under a magnetic field. During the carbonization of coal tar pitch, low-molecular-weight hydrocarbons (LMwHCs) melt, and the carbon crystallites aggregate into spherical domains behaving as single units. Magnetic alignment of spherical domains occurred readily in the liquid phase, and its solidification afforded a highly oriented graphite precursor. By optimizing the amounts of carbon crystallites and LMwHCs in the coal tar pitch during carbonization at 600–800 K, we increased the sphere size, thereby enhancing the orientation of carbon crystallites under the influence of a magnetic field. The increased size enhanced the magnetic torque exerted on these domains, making them more responsive to the applied magnetic field and easier to align. Carbonization upon thermal treatment at up to 1523 K achieved using the highly oriented precursor reduced the energy consumption by >25%, which illustrated the possibility of graphite preparation at even lower energies.

Polycyclic aromatic hydrocarbons (PAHs) form aggregates and exhibit excimer fluorescence when they are incorporated into poly-N-isopropylacrylamide (PNIPA) gel and placed in an aqueous environment. This aggregation dissipates rapidly owing to dehydration, causing a switch to monomer fluorescence. This reversible "phasing chromism" phenomenon ceases when the solubility of PAHs in water becomes very low; this is because PAHs undergo diffusion-controlled aggregation in PNIPA gel, resulting in rapid solid precipitation, as indicated by the numerous green light-emitting dendrites observed in the gel. Herein, phasing chromism in gels incorporated with tetracene (TE) was investigated using a mixture of water and tetrahydrofuran (THF) as a dispersant. Phasing chromism occurred when 20 % THF was added to the water in the gel. Controlling the solubility of PAHs is crucial for the appearance of phasing chromism. Based on the two-step nucleation theory, it can be inferred that the phasing chromism is attributable to changes in the Gibbs energy of the monomer in the swollen and contracted states. In addition, the selection of molecules for the phasing chromism can be enhanced by adjusting the Gibbs energy of the aggregated state based on the solubility of PAHs. These findings can promote the development of efficient and versatile light-emitting diodes.

The structure of carbon materials can be controlled using a magnetic field, enhancing their functional properties. Most of the magnetic-field effects on carbon material growth were found to originate from the magnetic-field orientation. However, we observed that the magnetic-field orientation did not affect the growth of single-walled carbon nanotubes (SWCNTs); instead, under a magnetic field of 10 T, the preferential growth of metallic SWCNTs (1-nm diameter) was observed using chemical vapor deposition and liquid decomposition, suggesting chirality selectivity. Raman and X-ray photoelectron spectra showed that the defect structure and oxygen content of SWCNTs increased with increasing magnetic-field intensity. Therefore, thin metallic nanotubes can be selectively grown by applying a high magnetic field in environments where nanotubes are relatively difficult to form.

For poly-N-isopropylacrylamide (PNIPA) gels with lower critical solution temperatures (LCSTs), a slight temperature shift dramatically changes the water content inside the gel. Unless bonded chemically, hydrophobic molecules—such as polycyclic aromatic hydrocarbons (PAHs)—added to the PNIPA gel aggregate to form a separate phase when the gel is in the swollen state and diffuse into the gel in the dehydrated state. This phenomenon can be leveraged by incorporating PAHs with energy transfer capabilities, such as anthracene (AN) and tetracene (TE), within a PNIPA gel and using the hydration state of the gel to modulate the distance between these molecules. Using this strategy, we were able to promote energy transfer in the aggregated state and suppress it in the dehydrated state of the gel. The emission from the energy-acceptor TE was dominant under accelerated energy transfer conditions, whereas when energy transfer was suppressed, emission from the AN excited species was also observed. The reversible transfer of energy, controlled by water absorption and dehydration, resulted in unprecedented luminescence chromism.

The magnetic moments of a magnetic ionic liquid, emim FeCl4, confined in the micropores and mesopores of SBA-15 with two different fractional pore fillings were measured over the temperature range of 1.8-300 K. The slightly negative Weiss temperature of the bulk decreased to 67 K above the high-temperature region more than 120 K in the system both micropores and mesopores filled. X-ray scattering profiles of the confined emim FeCl4 revealed that the magnetic anions confined in mesopores are loosely bounded to the pore walls, thus have unique magnetic properties.

Several fluorescence patterns derived from the excimer states of perylene have been reported, but most of these have been obtained from rigid forms such as crystals or for perylene embedded in hard polymers. We observed perylene excimer emission on absorption of water by a poly-N-isopropylacrylamide gel containing perylene molecules, which were not fixed to the gel framework by chemical bonding. We propose that this emission arises because the hydrophobic perylene molecules cannot dissolve in water and form aggregates. The perylene aggregation was quickly lost on dehydration of the gel, and the luminescence reverted to that of the monomer. In a dehydrated environment, perylene was rapidly dispersed in the gel network. In other words, solid-liquid phase separation of perylene was induced by uptake of water into the gel, and perylene dissolved in the gel on dehydration. Because the outside of the gel is always in an aqueous environment, perylene will remain semipermanently in the gel. Therefore, monomer emission and excimer emission can be switched reversibly and repeatedly.

Traditional carbon materials such as graphite are currently extremely useful and have recently been applied to cutting-edge materials. However, it is a concern that as production will increase much more in the future, the impact on the environment during preparation will become a problem. Recently, we have succeeded in obtaining an extremely high orientation structure using a carbonization process in a strong magnetic field [“Magnetic orientation of hexagonal carbon layers at high temperature” Chem. Lett. 41, 1576 (2012)]. Because graphite has a two-dimensional structure in which graphene sheets are laminated, we expect that graphitization should be easily performed by using a precursor that originally has an oriented structure. When two types of precursors prepared in the absence and presence of a magnetic field of 6 T were graphitized under the same conditions, graphitization was promoted by 50 to 100 K for the precursor to which a strong magnetic field was applied. If we fabricate products with the same degree of graphitization, it is calculated that the graphitization energy can be suppressed by as much as 10% by using a magnetic field. Applying this technology to the preparation of graphite in industry is proposed to result in substantial energy savings.

Magnetic ionic liquids (MIL) are a new type of ionic liquids that show paramagnetic response to magnetic fields. Here, we elucidate a plausible 3D liquid structure of the 1-ethyl-3-methyl-imidazolium tetrachloroferate (Emim [FeCl4]) and 1-butyl-3-methyl-imidazolium tetrachloroferate (Bmim[FeCl4]) MILs by X-ray scattering-aided hybrid reverse Monte Carlo simulations. Bmim[FeCl4] showed anomalously continuous structural changes over a wide temperature range (90-523 K) without crystallization, while Emim[FeCl4] displayed a melting point at 291 K with no glass transition. Conventional electron radial distribution function (ERDF) analysis provides misleading information about the structures of these MILs due to the mutual cancelation of the partial anion-anion and anion-cation ERDFs. Subsequent hybrid reverse Monte Carlo (HRMC) analysis revealed the precise coordination structures of both ionic liquids, and the alternating periodic arrangement of the anions and cations was visualized based on the HRMC simulation results. The results clearly revealed that the 1st coordination structure of the FeCl4 anion around the Bmim cation was widespread compared to that of the Emim cation, resulting in the absence of crystallization. In addition, we obtained new insights into the antiferromagnetic interaction between the FeCl4- ions of Bmim [FeCl4] even in the absence of the crystallization at low temperatures. Our results shed new light on the development of MILs not only for practical applications but also for the advancing the basic science of pure liquids with a high magnetic response. (C) 2020 Elsevier B.V. All rights reserved.

An ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA TFSI), was transformed from a liquid phase to another fluidic phase by application of the threshold magnetic field at constant temperature (T). The magnetic-field-induced (MFI) phase transformation was detected by the electric potential generated between two Pt electrodes set to the bottom and upper parts in a TMPA TFSI liquid during sweep of the magnetic field (B). The magnetic susceptibility and Verdet constant of TMPA TFSI also were slightly changed over 3 T. The MFI phase formation was almost completed within 3 h after TMPA TFSI liquid was exposed to a 6 T magnetic field, as demonstrated by the melting behavior of TMPA TFSI solid frozen instantaneously under 6 T. Multivariate analysis of the Raman spectra suggested that the MFI transformation should be associated with the conformational change of the transoid-to-cisoidlike species of TFSI ions. A B-T phase diagram of TMPA TFSI is proposed.

Pyrene (Py) contained in poly(N-isopropylacrylamide) gel (NIPA gel) that is swollen by water emits excimer-like derived fluorescence. However, as dehydration proceeded with increasing temperature, the luminescence changed to the monomer-derived one. Changes of it occurred continuously and reversibly around the lower critical solution temperature of NIPA gel. Because the gel interior becomes a hydrophobic environment in the shrunken state, the Py molecules can diffuse. However, it gathers like an oil droplet in the swollen gel by water. Reversible change of fluorescence wavelength with phase separation of Py according to hydration of NIPA gel represents an unprecedented type of chromism.

Carbon microcrystallites can become oriented in the carbonization process of coal tar pitch, which occurs with the characteristic where a mesophase is obtained, by using a magnetic field. An oriented film that has the ability to transmit visible light from 450 to 800nm can be obtained by sandwiching an appropriate amount of coal pitch between two glass plates and heating in an inert atmosphere at 793K under a magnetic field. This film can be used to obtain the same linearly polarized light as a commercially available polarizing element. The degree of orientation of the film prepared in a magnetic field of 3T is not sufficient to use as a polarizer, but a magnetic field of 6T is able to sufficiently suppress the passage of crossed polarized light. The electrical conductivity of the carbon film prepared at 793K is improved by 10 times by the application of a magnetic field of 10T. The electrical conductivity is sensitive to the magnetic field, and there is a possibility that it can be further improved by applying 10T or more. Coal tar pitch is the residue after obtaining coke from coal, and the optical and electrical advantage of a material prepared in the magnetic field derived from such natural products is clarified.

The influence of an applied magnetic field on the formation of carbon materials from coal tar pitch is investigated. Under an applied magnetic field, crystallites in a mesophase resembling liquid crystals are magnetically oriented during the carbonization process. Compared with that under a nonmagnetic field, carbonized coal tar pitch under a strong magnetic field of 10 T, generated by a superconducting magnet, has a highly oriented structure of carbon crystallites. The orientation of samples prepared under 2 T, which can easily be supplied by an electromagnet, was insufficient. Activation by potassium hydroxide is effective for affording a precursor for activated carbon. The activated carbon obtained under a strong magnetic field has a unique adsorption ability, which arises from its increase in relative surface area and total pore volume compared with those of an activated carbon sample prepared from a precursor produced under zero magnetic field. The precursor carbonized under a magnetic field of 10 T contains a larger number of crystallites than that carbonized under a 0-T magnetic field, which leads to high-performance activated carbon.

Understanding the polymorph phenomenon for organic crystals is essential for the development of organic solid materials. Here, the fluorescence study of the evaporative crystallization of 1,3-dipyrrol-2-yl-1,3-propanedione boron difluoride complex (1), which has three polymorphs showing different emission profiles, is reported. The droplet of 1 in 1,2-dichloroethane showed blue emission just after dropping. Solids with bluish-green emission were observed. As time elapsed, a solid with red or orange emission was observed around the droplet. Time evolution of the fluorescence spectra, observed for the first time, implied that the molten state of 1 was observed by emission of an intermediate, even at ambient temperature. These findings suggested that the liquid-like cluster incidentally forms an ordered array as the crystallites nucleate. The liquid-like cluster can be considered as the "crucible" in the nucleation of polymorphs.

Microspaces can simultaneously capture "immiscible" molecules such as cyclohexane and water due to fluid-surface interactions. We investigated the mesoscopic structure of cyclohexane and water co-adsorbed in carbon micropores using contrast variation small-angle neutron scattering (CV-SANS). The results show that cyclohexane tends to adsorb near the carbon surface and that both molecules form relatively small domains (<1 nm).