Electrofluorochromic Hydrogels by Oligothiophene-Based Color-Tunable Fluorescent Dye Doping.

Soft electronic materials hold great promise for advancing flexible functional devices. Among the various soft materials available, hydrogels are particularly attractive for soft electronic device development due to their inherent properties, including transparency, shape adaptability through swelling/deswelling, and self-healing capabilities. Transparent hydrogels contribute to the creation of advanced smart devices such as sensors, smart windows, and anticounterfeiting technologies. Poly(vinyl alcohol) hydrogels are used as a platform for creating electrofluorochromic (EFC) devices in combination with oligothiophene-conjugated benzothiazole derivatives (OCBs) as fluorescent emitters. OCBs demonstrated excited-state intramolecular proton transfer (ESIPT) behavior with a large Stokes shift and emission changes responsive to solvent polarity and pH stimuli. Even in the solid state, OCBs exhibited strong fluorescence emission across a wide range of colors from blue to red, making them exceptionally well-suited for EFC device development. Their quantum yields in the powder state were obtained between 2.3% and 19.9%. Through the incorporation of OCBs into a PVA hydrogel (OCB@PVA), we achieved the successful fabrication of flexible EFC devices, including electronic paper and smart panels. When electric potentials (-2.4 and +2.4 V) were applied in OCB@PVA, fluorescence color changes were observed by an electrochemically induced pH change owing to electrohydrolysis of water. These devices demonstrated the potential of OCB@PVA hydrogels in the realm of flexible electronics. They could be used to create innovative and versatile devices with stimuli-responsive fluorescence properties.

Recognition of atomic-level difference in porphyrin dyads for self-sorted supramolecular polymer growth.

Porphyrin dyads (PDMs, where M = Zn and Cu) composed of diphenylporphyrin and tetraphenylporphyrin units, designated as DPDMs and TPDMs, respectively, exhibited remarkable differences in the molecular assemblies depending on the coordination metal ion. Furthermore, TPDMs showed self-sorting behavior during the formation of supramolecular assemblies through the recognition of atomic-level difference.

Retention of Intrinsic Photophysical Properties of Porphyrin Building Blocks in 3D Organic Frameworks through Magic Angle Alignment.

Construction of three-dimensional (3D) frameworks maintaining intrinsic photophysical properties of monomeric building blocks is difficult and challenging due to the existence of various molecular interactions, such as metal-organic and π-π interactions. A 3D hydrogen-bonded organic framework (YSH-1Zn) with permanent porosity was constructed using a porphyrin having six carboxylic acid groups (1Zn). Brunauer-Emmett-Teller surface area measurement indicated that YSH-1Zn has a porous structure with a surface area of 392 m2/g. Single-crystal X-ray diffraction analysis revealed that 1Zn creates a 5-fold interwoven 3D network structure adopting a monoclinic system with a space group of P21/c. Each 1Zn within a single crystal exhibits parallel alignment with a slip-stack angle of 54.6°, in good agreement with the magic angle. Although the center-to-center distance of the nearest zinc atoms in YSH-1Zn is only 5.181 Å, the UV/vis absorption and fluorescence emission of YSH-1Zn are not different from those of 1Zn, indicating the absence of an interaction between excitons. Due to the magic angle alignment of 1Zn, the fluorescence lifetime, decay profiles, and quantum yield remained uniform even in the solid state.

Graft onto approaches for nanocellulose-based advanced functional materials.

The resurgence of cellulose as nano-dimensional 'nanocellulose' has unlocked a sustainable bioeconomy for the development of advanced functional biomaterials. Bestowed with multifunctional attributes, such as renewability and abundance of its source, biodegradability, biocompatibility, superior mechanical, optical, and rheological properties, tunable self-assembly and surface chemistry, nanocellulose presents exclusive opportunities for a wide range of novel applications. However, to alleviate its intrinsic hydrophilicity-related constraints surface functionalization is inevitably needed to foster various targeted applications. The abundant surface hydroxyl groups on nanocellulose offer opportunities for grafting small molecules or macromolecular entities using either a 'graft onto' or 'graft from' approach, resulting in materials with distinctive functionalities. Most of the reviews published to date extensively discussed 'graft from' modification approaches, however 'graft onto' approaches are not well discussed. Hence, this review aims to provide a comprehensive summary of 'graft onto' approaches. Furthermore, insight into some of the recently emerging applications of this grafted nanocellulose including advanced nanocomposite formulation, stimuli-responsive materials, bioimaging, sensing, biomedicine, packaging, and wastewater treatment has also been reviewed.

Asymmetric gradient orbital interaction of hetero-diatomic active sites for promoting C - C coupling.

Diatomic-site catalysts (DACs) garner tremendous attention for selective CO2 photoreduction, especially in the thermodynamical and kinetical mechanism of CO2 to C2+ products. Herein, we first engineer a novel Zn-porphyrin/RuCu-pincer complex DAC (ZnPor-RuCuDAC). The heteronuclear ZnPor-RuCuDAC exhibits the best acetate selectivity (95.1%), while the homoatomic counterparts (ZnPor-Ru2DAC and ZnPor-Cu2DAC) present the best CO selectivity. In-situ spectroscopic measurements reveal that the heteronuclear Ru-Cu sites easily appear C1 intermediate coupling. The in-depth analyses confirm that due to the strong gradient orbital coupling of Ru4d-Cu3d resonance, two formed *CO intermediates of Ru-Cu heteroatom show a significantly weaker electrostatic repulsion for an asymmetric charge distribution, which result from a side-to-side absorption and narrow dihedral angle distortion. Moreover, the strongly overlapped Ru/Cu-d and CO molecular orbitals split into bonding and antibonding orbitals easily, resulting in decreasing energy splitting levels of C1 intermediates. These results collectively augment the collision probability of the two *CO intermediates on heteronuclear DACs. This work first provides a crucial perspective on the symmetry-forbidden coupling mechanism of C1 intermediates on diatomic sites.

Impact of peripheral alkyl chain length on mesocrystal assemblies of G2 dendrons.

Unique sphere-packing mesophases such as Frank-Kasper (FK) phases have emerged from the viable design of intermolecular interactions in supramolecular assemblies. Herein, a series of Cn-G2-CONH2 dendrons possessing an identical core wedge are investigated to elucidate the impact of peripheral alkyl chain lengths (Cn) on the formation of the close-packed structures. The C18 and C14 dendrons, of which the contour lengths of the periphery Lp are longer than the wedge length Lw, assemble into a uniform sphere-packing phase such as body-centred cubic (BCC), whereas the C8 dendron with short (Lp < Lw) corona environment forms the FK A15 phase. Particularly in the intermediate C12 and C10 dendrons (Lp ≈ Lw), cooling the samples from an isotropic state leads to cooling-rate-dependent phase behaviours. The C12 dendron produces two structures of hexagonal columnar and sphere-packing phases (BCC and A15), while the C10 dendron generates the A15 and σ phases by the fast- and slow-cooling processes, respectively. Our results show the impact of peripheral alkyl chain lengths on the formation of mesocrystal phases, where the energy landscape of the dendrons at Lp/Lw ≈ 1 must be more complex and delicate than those with either longer or shorter peripheral alkyl chains.

Porphyrin-based supramolecular polymers.

Porphyrin derivatives are ubiquitous in bio-organisms and are associated with proteins that play important biological roles, such as oxygen transport, photosynthesis, and catalysis. Porphyrins are very fascinating research objects for chemists, physicists, and biologists owing to their versatile chemical and physical properties. Porphyrin derivatives are actively used in various fields, such as molecular recognition, energy conversion, sensors, biomedicine, and catalysts. Porphyrin derivatives can be used as building blocks for supramolecular polymers because their primitive structures have C4 symmetry, which allows for the symmetrical introduction of self-assembling motifs. This review describes the fabrication of porphyrin-based supramolecular polymers and novel discoveries in supramolecular polymer growth. First, we summarise the (i) design concepts, (ii) growth mechanism and (iii) analytical methods of porphyrin-based supramolecular polymers. Then, the examples of porphyrin-based supramolecular polymers formed by (iv) hydrogen bonding, (v) metal coordination-based interaction, (vi) host-guest complex formation, and (vii) others are summarised. Finally, (viii) applications and perspectives are discussed. Although supramolecular polymers, in a broad sense, can include either two-dimensional (2D) networks or three-dimensional (3D) porous polymer structures; this review mainly focuses on one-dimensional (1D) fibrous supramolecular polymer structures.

Apex hydrogen bonds in dendron assemblies modulate close-packed mesocrystal structures.

The close-packed mesocrystal structures from soft-matter assemblies have recently received attention due to their structural similarity to atomic crystals, displaying various sphere-packing Frank-Kasper (FK) and quasicrystal structures. Herein, diverse mesocrystal structures are explored in second-generation dendrons (G2-X) designed with identical wedges, in which the terminal functionalities X = CONH2 and CH2NH2 represent two levels of the strong and weak hydrogen-bonding apexes, respectively. The cohesive interactions at the core apex, referred to as the core interactions, are effectively modulated by forming heterogeneous hydrogen bonds between these two functional units. For the dendron assemblies compositionally close to each pure component of G2-CONH2 and G2-CH2NH2, their own FK A15 and C14 phases dominate other phases, respectively. We show the existence of the wide-range FK σ including the dodecagonal quasicrystal (DDQC) phases from the dendron mixtures between G2-CONH2 and G2-CH2NH2, providing an experimental phase sequence of A15-σ-DDQC-C14 as the core interactions are alleviated. Intriguingly, the temperature dependence of particle sizes shows that the high plateau values of particle sizes are maintained equivalently until each threshold temperature (Tth), followed by a prompt decrease above the Tth. A decrease in Tth by alleviating the core interactions and its composition dependence suggest that the more size-dispersed particles, the more susceptibility to chain exchange with increasing temperature. Our results on the formation of supramolecular dendron assemblies provide a guide to understand the core-interaction-dependent mesocrystal structures toward the fundamental principle underlying the temperature dependence of their particle sizes.

Spontaneously sp2-Carbonized Fluorescent Polyamides as a Probe Material for Bioimaging.

Spontaneously sp2-carbonized polyamides (PA1, PA2) were prepared via Knoevenagel-type side reactions of malonyl moieties under mild conditions in the polycondensation of dicarbonyl chloride and diamine. Both polymers were soluble in water and emissive in the visible region, and the fluorescence (FL) intensity and the maximum wavelength were highly dependent on the excitation wavelength and the pH. Their chemical structures and FL origin were clarified by performing various spectroscopic analyses. π*-π transition was assumed to be allowed in an enol form based on the conjugated structure formed by the side reaction; this was responsible for its pH dependency and high FL quantum efficiency. In particular, PA2, which comprises the tertiary amide linkage, showed quick endocytosis, low cytotoxicity, excellent biocompatibility, and exclusively stained lysosomes with the lowest intracellular pH. These results will help in understanding the origin of the FL emission of carbonized nanomaterials and exploring more advanced functions in the field of bioimaging.

The discrete single-entity electrochemistry of Pickering emulsions.

Single-entity analysis is an important research topic in electrochemistry. To date, electrode collisions and subsequent electrode-particle interactions have been studied for many types of nano-objects, including metals, polymers, and micelles. Here we extend this nano-object electrochemistry analysis to Pickering emulsions for the first time. The electrochemistry of Pickering emulsions is important because the internal space of a Pickering emulsion can serve as a reactor or template; this leads to myriad possible applications, all the while maintaining mechanical stability far superior to what is exhibited by conventional emulsions. This work showed that Pickering emulsions exhibit similar hydrodynamic behavior to other nano-objects, despite the complex structure involving hard nanoparticle surfactants, and the electron-transport mechanism into the internal volume of Pickering emulsions was elucidated. The Pickering emulsion electrochemistry platform developed here can be applied to electrochemical nanomaterial synthesis, surmounting the challenges faced by conventional synthetic strategies involving normal emulsions.

Mesoscale Frank-Kasper Crystal Structures from Dendron Assembly by Controlling Core Apex Interactions.

Single-component polymeric materials open up a great potential for self-assembly into mesoscale complex crystal structures that are known as Frank-Kasper (FK) phases. Predicting the packing structures of the soft-matter spheres, however, remains a challenge even when the molecular design is precisely known. Here, we investigate the role of the molecules' enthalpic interaction in determining the low-symmetry crystal structures. To this end, we synthesize architecturally asymmetric dendrons by varying their apex functionalities and examine the packing structures of the second-generation (G2) dendritic wedges. Our work shows that weakening the hydrogen bonding of the dendron apex makes the particles softer and smaller, and leads to the formation of various FK structures at lower temperatures, including the new observation of a FK C14 phase in the cone-shaped dendron systems. As a consequence of the free energy balance between the particle's interfacial tension and the chain's stretching, various packing structures are mainly tuned by designing the hydrogen bonding interaction.

Bioinspired Applications of Porphyrin Derivatives.

Porphyrin derivatives are ubiquitous in nature and have important biological roles, such as in light harvesting, oxygen transport, and catalysis. Owing to their intrinsic π-conjugated structure, porphyrin derivatives exhibit characteristic photophysical and electrochemical properties. In biological systems, porphyrin derivatives are associated with various protein molecules through noncovalent interactions. For example, hemoglobin, which is responsible for oxygen transport in most vertebrates, consists of four subunits of a globular protein with an iron porphyrin derivative prosthetic group. Furthermore, noncovalently arranged porphyrin derivatives are the fundamental chromophores in light-harvesting systems for photosynthesis in plants and algae. These biologically important roles originate from the functional versatility of porphyrin derivatives. Specifically, porphyrins are excellent host compounds, forming coordination complexes with various metal ions that adds functionality to the porphyrin unit, such as redox activity and additional ligand binding at the central metal ion. In addition, porphyrins are useful building blocks for functional supramolecular assemblies because of their flat and symmetrical molecular architectures, and their excellent photophysical properties are typically utilized for the fabrication of bioactive functional materials. In this Account, we summarize our endeavors over the past decade to develop functional materials based on porphyrin derivatives using bioinspired approaches. In the first section, we discuss several synthetic receptors that act as artificial allosteric host systems and can be used for the selective detection of various chemicals, such as cyanide, chloride, and amino acids. In the second section, we introduce multiporphyrin arrays as mimics of natural light-harvesting complexes. The active control of energy transfer processes by additional guest binding and the fabrication of organic photovoltaic devices using porphyrin derivatives are also introduced. In the third section, we introduce several types of porphyrin-based supramolecular assemblies. Through noncovalent interactions such as metal-ligand interaction, hydrogen bonding, and π-π interaction, porphyrin derivatives were constructed as supramolecular polymers with formation of fiber or toroidal assembly. In the last section, the application of porphyrin derivatives for biomedical nanodevice fabrication is introduced. Even though porphyrins were good candidates as photosensitizers for photodynamic therapy, they have limitations for biomedical application owing to aggregation in aqueous media. We suggested ionic dendrimer porphyrins and they showed excellent photodynamic therapy (PDT) efficacy.

Silicon Tetrapyrazinoporphyrazine Derivatives-Incorporated Carbohydrate-Based Block Copolymer Micelles for Photodynamic Therapy.

Developing nonaggregated photosensitizers (PSs) for efficient photodynamic therapy (PDT) using polymeric micelles (PMs) has been challenging. In this study, axially substituted nonaggregated silicon tetrapyrazinoporphyrazine (SiTPyzPz) derivatives in carbohydrate-based block glycopolymer-based PMs were designed and used as PSs for PDT. To achieve the nonaggregated PSs, SiTPyzPz was axially substituted with trihexylsiloxy (THS) groups to form SiTPyzPz-THS, which exhibited highly monomeric behaviors in organic solvents. Moreover, three block copolymers were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Each copolymer comprised hydrophobic polystyrene blocks and loadable SiTPyzPz-THS, and one or two consisted of two possible hydrophilic blocks, polyethylene glycol or poly(glucosylethyl methacrylate). The self-assembly of SiTPyzPz-THS and the block copolymers in aqueous solvents induced the formation of spherical PMs with core-shell or core-shell-corona structures. The SiTPyzPz-THS in the PMs exhibited monomeric state, intense fluorescence emission, and outstanding singlet oxygen generation; moreover, it did not form aggregates. During the in vitro test, which was performed to investigate the PDT efficiency, the PMs, which consisted of poly(glucosylethyl methacrylate) shells, exhibited high photocytotoxicity and cellular internalization ability. Consequently, the PM systems of nonaggregated PSs and carbohydrate-based block copolymers could become very promising materials for PDT owing to their photophysicochemical properties and considerable selectivity against cancer cells.

Enhancement of Energy Transfer Efficiency with Structural Control of Multichromophore Light-Harvesting Assembly.

Multichromophore systems (MCSs) are envisioned as building blocks of molecular optoelectronic devices. While it is important to understand the characteristics of energy transfer in MCSs, the effect of multiple donors on energy transfer has not been understood completely, mainly due to the lack of a platform to investigate such an effect systematically. Here, a systematic study on how the number of donors (n D) and interchromophore distances affect the efficiency of energy transfer (η FRET) is presented. Specifically, η FRET is calculated for a series of model MCSs using simulations, a series of multiporphyrin dendrimers with systematic variation of n D and interdonor distances is synthesized, and η FRETs of those dendrimers using transient absorption spectroscopy are measured. The simulations predict η FRET in the multiporphyrin dendrimers well. In particular, it is found that η FRET is enhanced by donor-to-donor energy transfer only when structural heterogeneity exists in an MCS, and the relationships between the η FRET enhancement and the structural parameters of the MCS are revealed.

Cancer cell death using metabolic glycan labelling techniques.

Herein we describe a method for inducing cancer cell death, which relies on the use of a H2O2-responsive glycan metabolic precursor in conjunction with antibody-dependent cellular cytotoxicity (ADCC) or photodynamic therapy (PDT).

Strapped calix[4]pyrrole as a lithium salts selective receptor through separated ion-pair binding.

A triazole-bearing strapped calix[4]pyrrole (1) was synthesized as a lithium salt selective ion pair receptor. 1H NMR spectral studies and X-ray crystallography showed that the capture of LiCl by 1 occurs via separated ion pair binding. Furthermore, lithium salts extracted by 1 could be solidified in the form of Li2CO3 through CO2 or K2CO3 treatment.

Bacterial Lectin-Targeting Glycoconjugates for Selective Elimination of Pathogenic Bacteria.

Herein we report a strategy to eradicate pathogenic bacteria selectively, which utilizes bacterial lectin-targeting glycoconjugates that contain an epitope or a photosensitizer to promote antibody-dependent cellular cytotoxicity (ADCC) or photodynamic therapy (PDT), respectively. Our results show that death promoted by using the designed synthetic glycoconjugates coupled with ADCC or PDT takes place selectively in pathogenic bacteria expressing lectins on their surfaces.

Cyclodextrin-bearing telechelic poly(2-isopropyl-2-oxazoline): Extremely large shifts of phase transition temperature by photo-responsive guest inclusion.

As a dual-stimuli-responsive polymer, α-cyclodextrin-bearing telechelic poly(2-isopropyl-2-oxazoline) (CD-PiPrOx-CD) was prepared by living cationic ring opening polymerization followed by click reaction (copper-catalyzed alkyne-azide cycloaddition). The phase transition temperature (TCP) of CD-PiPrOx-CD (0.33 mM) in 10 mM PBS solution (150 mM NaCl, pH 7.4) was 42.9 °C, and dramatically changed to 8.5 °C upon addition of the azobenzene-bearing penta(ethylene glycol) (Az-5EG) (3.3 mM). A change in the TCP was again observed for the mixture solution of CD-PiPrOx-CD and Az-5EG upon ultra-violet (UV) irradiation at 365 nm. Under 365-nm UV irradiation for 30 min, the TCP of CD-PiPrOx-CD changed to 41.3 °C, indicating the release of Az-5EG from the host-guest complex. During alternate irradiation at 365 and 254 nm, the TCP changed in a fully reversible manner.

Metal-organic framework based on hinged cube tessellation as transformable mechanical metamaterial.

Mechanical metamaterials exhibit unusual properties, such as negative Poisson's ratio, which are difficult to achieve in conventional materials. Rational design of mechanical metamaterials at the microscale is becoming popular partly because of the advance in three-dimensional printing technologies. However, incorporating movable building blocks inside solids, thereby enabling us to manipulate mechanical movement at the molecular scale, has been a difficult task. Here, we report a metal-organic framework, self-assembled from a porphyrin linker and a new type of Zn-based secondary building unit, serving as a joint in a hinged cube tessellation. Detailed structural analysis and theoretical calculation show that this material is a mechanical metamaterial exhibiting auxetic behavior. This work demonstrates that the topology of the framework and flexible hinges inside the structure are intimately related to the mechanical properties of the material, providing a guideline for the rational design of mechanically responsive metal-organic frameworks.

Hierarchical Hybrid Nanostructures Constructed by Fullerene and Molecular Tweezer.

For the construction of well-defined hierarchical superstructures of pristine [60]fullerene (C60) arrays, pyrene-based molecular tweezers (PT) were used as host molecules for catching and arranging C60 guest molecules. The formation of host-guest complexes was systematically studied in solution as well as in the solid state. Two-dimensional proton nuclear magnetic resonance spectroscopic studies revealed that PT-host and C60-guest complexes were closely related to the molecular self-assembly of PT. Ultraviolet and fluorescence spectroscopic titrations indicated the formation of stable 1:1 and 2:1 (PT/C60) complexes. From the nonlinear curve-fitting analysis, equilibrium constants for the 1:1 (log K1) and 2:1 (log K2) complexes were estimated to be 4.96 and 5.01, respectively. X-ray diffraction results combined with transmission electron microscopy observations clearly exhibited the construction of well-defined layered superstructures of the PT-host and C60-guest complexes. From electron mobility measurements, it was demonstrated that the well-defined hierarchical hybrid nanostructure incorporating a C60 array exhibited a high electron mobility of 1.7 × 10-2 cm2 V-1 s-1. This study can provide a guideline for the hierarchical hybrid nanostructures of host-guest complex and its applications.