Fumitaka Ishiwari

• Professor (Associate) at Osaka University

The development of a new molecular building block for the construction of elaborated molecular assemblies extends the chemical space for materials exploration. While representative organic components for the design of chiral porous materials adopt C1- and C2-symmetries, the use of more symmetric components has been underexplored due to syn-thetic l...

The design of well‐defined assemblies of chiral molecules is a prerequisite for numerous applications, such as chirality‐induced spin selectivity (CISS). In this context, tripodal molecular films bear the advantage of better control of molecular orientation and alignment than analogous monopodal systems. To this end, we report on the synthesis and...

Tin-based halide perovskite solar cells (Sn PSCs) have unacceptably low open-circuit voltages owing to the severe carrier traps induced by the facile oxidation of Sn²⁺. To prevent oxidation, Sn powder is often added to the precursor solutions; however, the optimal process conditions and the detailed underlying mechanism remain elusive. Here, the PS...

Liquid crystalline poly(substituted methylene)s (PMs) with side-on mesogens exhibit reversible birefringence (Δn) inversion during liquid crystal (LC)-to-LC phase transitions as the temperature increases. The low-temperature LC phase exhibits a positive...

The quadrupole moment of a non-fullerene acceptor (NFA) generated by the constituent electron donor (D) and acceptor (A) units is a significant factor that affects the charge separation (CS) and charge recombination (CR) processes in organic photovoltaics (OPVs). However, its impact on p-type polymer domains remains unclear. In this study, we synth...

A nonporous [Pb(tadt)]n (tadt = 1,3,4‐thiadiazole‐2,5‐dithiolate) coordination polymer, KGF‐9, with a 2D infinite (−Pb−S−)n structure has been previously reported as a precious‐metal‐free photocatalyst for selective CO2‐to‐formate conversion under visible light. In the present work, a microwave (MW)‐assisted solvothermal reaction is used to synthes...

Electronic molecules with a BN‐heterocyclic and carbon‐based aromatic hybrid ring system (h‐CBN) are interesting in that they potentially exhibit synergistic properties arising from the two different π‐systems. Here we report the synthesis and properties of a h‐CBN‐type molecule (1) having a bicyclic B4N4‐heteropentalene core fused with extended ar...

Halide anion migration in organic–inorganic metal halide perovskites significantly influences the power conversion efficiency (PCE) and hysteresis of perovskite solar cells (PSCs). These materials are sensitive to various external stimuli such as light, heat, and electrical bias, highlighting the need for novel post‐manufacturing treatment methods...

Figure-eight-shaped nonplanar π-systems adopt distinctive chiral D2-symmetric structures, which are ideal for realizing efficient circularly polarized luminescence (CPL). However, the short-step and enantioselective synthesis of figure-eight π-systems represents a considerable challenge for the conventional bottom-up synthetic strategy. Herein, we...

Novel optically active π-conjugated polymers having a chiral bifacial indacenodithiophene backbone were synthesized by Suzuki-Miyaura cross coupling polymerization with benzothiadiazole comonomer. The obtained C 2 -chiral polymers form amorphous thin films on...

The widespread use of tin dioxide (SnO2) thin films as electron transport layer (ETL) of perovskite solar cells (PSCs) has been facilitated by commercial SnO2 nanocolloid dispersion. Nevertheless, challenges such as nanoparticle agglomeration have emerged, impacting film quality and interface properties critical for PSC performance. Herein, the eff...

Controlling the rotation of carbon–carbon bonds, which is ubiquitous in organic molecules, to create functionality has been a subject of interest for a long time. In this context, it would be interesting to explore whether cooperative and collective rotation could occur if dipolar molecular rotors were aligned close together while leaving adequate...

Triptycene, a rigid propeller-shaped molecule, was first synthesized in the early 1940s. More recently, many triptycene-containing polymers and molecular assemblies have been developed for a wide range of applications, including guest recognition, material transport, separation, catalysis, and as device components. The advantages of triptycenes lie...

Cyclic anthraquinodimethane (AQD) dimer with a highly constrained structure was synthesized by using the Au-templated method. X-ray diffraction analysis and UV-Vis spectroscopy revealed that the AQD skeleton adopts a deeply folded structure and exhibits red-shifted absorptions in the dimer compared to those in non-cyclized monomeric AQD. Due to the...

The development of a highly active photocatalyst for visible‐light water splitting requires a high‐quality semiconductor material and a cocatalyst, which promote both the migration of photogenerated charge carriers and surface redox reactions. In this work, a cocatalyst was loaded onto an oxyfluoride photocatalyst, Pb2Ti2O5.4F1.2, to improve the wa...

The molecular conformation, crystalline morphology, and properties of photochromic organic crystals can be controlled through photoirradiation, making them promising candidates for functional organic materials. However, photochromic porous molecular crystals with a networked framework structure are rare due to the difficulty in maintaining space th...

Contemporary synthetic strategies in organic chemistry rely heavily on the stepwise formation of bonds between fragments of the target compound (‘bottom-up’ approach). Figure-eight aromatic macrocycles represent a considerable challenge for the bottom-up approach, and the lack of versatile synthetic routes to such macrocycles prevents the use of th...

Controlling the rotation of carbon-carbon bonds, which is ubiquitous in organic molecules, to create functionality has been a subject of interest for a long time. In this context, it would be interesting to explore whether cooperative and collective rotation could occur if dipolar molecular rotors were aligned close together while leaving adequate...

The molecular conformation, crystalline morphology, and properties of photochromic organic crystals can be controlled through photoirradiation, making them promising candidates for functional organic materials. However, photochromic porous molecular crystals with a networked framework structure are rare due to the difficulty in maintaining space th...

Significant effort has been devoted to creating new molecules that show circularly polarized luminescence (CPL) and can be used in devices from both experimental and theoretical approaches. Here we show a new design strategy to achieve a large dissymmetric factor (g value) for CPL based on the symmetry-forbidden transition of π-conjugated molecules...

Correction for ‘Water-dispersible donor–acceptor–donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change’ by Tomoya Enjou et al. , Chem. Commun. , 2024, https://doi.org/10.1039/d3cc05749f.

Novel water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles, having dibenzophenazine as the acceptor and heteroatom-bridged amphiphilic diarylamines as the donors, have been developed. The materials displayed distinct photoluminescence color change in response to...

Considerable efforts have been devoted to the development of new organic‐inorganic hybrid perovskites as well as their passivation‐layer materials to improve the performance of solution‐processable thin‐film solar cells for practical applications. For this purpose, monocations, such as monoammonium ions, have been studied extensively as organic bui...

Development of two-dimensional materials and exploration of their functionalities are significant challenges due to their potential. In this study, we successfully fabricated a supramolecular nanosheet composed of amphiphilic Rose Bengal...

We designed new C 2 - and C 3 -symmetric molecules for passivating lead halide perovskite solar cells (PSCs). These unique bifacial molecules enable efficient hole transfer, defect passivation, and improved efficiency and stability.

The Pb–S‐based coordination polymer (CP), named KGF‐9, [Pb(tadt)]n (tadt = 1,3,4‐thiadiazole‐2,5‐dithiolate), can selectively convert CO2 into HCOO⁻ (>99%) under visible light, with an apparent quantum yield (AQY) of 2.6% at 400 nm, without a cocatalyst. However, KGF‐9 is an intrinsically nonporous CP, and its small specific surface area (<1 m² g⁻¹...

Solution-processed inorganic solar cells with less toxic and earth-abundant elements are emerging as viable alternatives to high-performance lead-halide perovskite solar cells. However, the wide range of elements and process parameters impede the rapid exploration of vast chemical spaces. Here, we developed an automated robot-embedded measurement s...

1,1’,10,10’‐Biphenothiazine and its S,S,S’,S’‐tetroxide are diaza[5]helicenes with N−N linkages. Kinetic experiments on racemization together with DFT calculations revealed that they undergo inversion through the N−N bond breaking pathway rather than the general conformational pathway. In these diaza[5]helicenes with this inversion mechanism, the r...

Expanded carbohelicenes with structures fused to 15- and 17-benzene were successfully synthesized. Establishing a new synthetic strategy is crucial to realize the development of longer expanded [2,1][n]helicenes with a kekulene-like projection drawing structure. This article describes the sequential integration of the π-elongating Wittig reaction o...

The bulk heterojunction structures of organic photovoltaics (OPVs) have been overlooked in their machine learning (ML) approach despite their presumably significant impact on power conversion efficiency (PCE). In this study, we examined the use of atomic force microscopy (AFM) images to construct an ML model for predicting the PCE of polymer : non-...

The elegant architectures of nonplanar π-systems, such as fullerene and corannulene, exhibit distinctive functionalities that have played a significant role in advancing science and technology. The current approach to synthesizing nonplanar π-systems heavily relies on the stepwise formation of bonds between their constituent fragments, which is kno...

Surface passivation is key to the power conversion efficiency (PCE) of organic-inorganic lead halide perovskite solar cells (PSCs). Herein, we report a novel molecular concept of a C2-symmetric syn-type bifacial donor-π-donor (D-π-D) passivation molecule (a racemic mixture of enantiomers) with hydrophobic phenyls and hydrophilic tetraethylene glyco...

We newly synthesized a series of homo‐ and hetero‐tetracene (Tc) oligomers to propose a molecular design strategy for the efficient exciton transport in linear oligomers by promoting correlated triplet pair (TT) dissociation and controlling sequential exciton trapping process of individual doubled triplet excitons (T+T) by intramolecular singlet fi...

The monomolecular assembly of 1,8,13-tricarboxytriptycene (Trip-CA) on a test oxide substrate, represented by indium tin oxide (ITO), was studied. For this purpose, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, contact angle goniometry, and work function measurements were used. The quality and the paramet...

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal...

Due to its unique physical and chemical properties, polydimethylsiloxane (PDMS) is widely used in many applications, in which covalent cross-linking is commonly used to cure the fluidic polymer. The formation...

Expanded carbohelicenes with structures fused to 15- and 17-benzene were successfully synthesized. Establishing a new synthetic strategy is crucial to realize the development of longer expanded [2,1][n]helicenes with a kekulene-like projection drawing structure. This article describes the sequential integration of the π-elongating Wittig reaction o...

We newly synthesized a series of homo‐ and hetero‐tetracene (Tc) oligomers to propose a molecular design strategy for the efficient exciton transport in linear oligomers by promoting correlated triplet pair (TT) dissociation and controlling sequential exciton trapping process of individual doubled triplet excitons (T+T) by intramolecular singlet fi...

Conjugated polymers encompassing delocalized π-electrons in their backbones exhibit high photoabsorption and efficient charge carrier transport through the intermolecular π-π stacking suitable for organic photovoltaics (OPV). By contrast, small molecules such as [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives, which demonstrates high fiel...

Dynamic mechanical chirality of [2]rotaxane consisting of a C s symmetric wheel and a C 2v symmetric axle is discussed via the synthesis, enantiomer separation, racemization, and chiral-prochiral interconversion. This [2]rotaxane is achiral and/or prochiral when its wheel locates at the center of the axle, but becomes chiral when the wheel moves fr...

The conventional development of organic photovoltaic (OPV) materials has been driven by the inspiration and continuous endeavors of experimentalists, whereas machine learning (ML) approaches enable extremely high-throughput data processing. However, the predictive accuracy of ML currently remains insufficient for the design of OPV semiconductors th...

Organic–inorganic lead halide perovskite solar cells (PSCs) are well suited for use in spacecrafts owing to their potentially high radiation tolerance and high mass specific power. However, the optimal device structure and charge transport material (hole-transport material, HTM; electron transfer material, ETM) have remained elusive. Herein, we ext...

Molecules with tripodal anchoring to substrates represent a versatile platform for the fabrication of robust self-assembled monolayers (SAMs), complementing the conventional monopodal approach. In this context, we studied the adsorption of 1,8,13-tricarboxytriptycene (Trip-CA) on Ag(111), mimicked by a bilayer of silver atoms underpotentially depos...

Triggered by the notable evolution of organic-inorganic metal halide perovskite solar cells (PSCs) with three-dimensional (3D) ABX3 (A: organic/inorganic cation, B: metal cation, X: halogen anion) structures, Ruddlesden-Popper two-dimensional (2D) pseudo perovskites given by An+1BnX3n+1 (n = 1, 2, …) are also becoming a material of interest, as the...

Dibenzo‐1,5‐diazacyclooctane (DACO) derivative undergoes two‐step protonation and would be useful for developing multistep stimuli‐responsive systems. The first proton (the brown cat) affords a proton‐bridged Tröger's‐base‐like pseudo bicyclic structure, and the second proton (the blue and white cats) causes an electrostatic repulsion between posit...

Hybrid ladder polymers containing Tröger's base (TB) and diazacyclooctane (DACO) units in the main chain with various contents of DACO unit were systematically synthesized by sequential post‐polymerization modification including N‐methylation and alkaline hydrolysis of TB‐based ladder polymers to investigate the effect of DACO content on the therma...

The conformational control of a dibenzo‐1,5‐diazacyclooctane (DACO) derivative with tertiary and secondary amino groups by stepwise protonation is investigated by single crystal X‐ray diffraction analysis, computational simulation, and variable temperature NMR measurements. The DACO derivative undergoes two‐step protonation, to afford bent‐shape mo...

The chemical structure of a branch point of star-shaped polymers has been considered to have small influence on the physical properties of the entire polymers. Contrary to this general notion,...

A polymer of intrinsic microporosity (PIMs) consisting of Tröger's base (TB) undergoes ring opening of the bicyclic amine upon N ‐methylation followed by alkaline hydrolysis, resulting in a hybrid ladder polymer that contains diazacyclooctane (DACO) units with tert ‐and sec ‐amino groups. The hybrid ladder polymers with various TB/DACO ratios can b...

Using a molecular engineering technique based on a tripodal triptycene-based supramolecular scaffold capable of precisely controlling molecular orientation on solid substrates, in combination with a time-domain thermoreflectance (TDTR) measurement technique, we evaluate thermal transport properties of a highly oriented long alkyl chain at the nanos...

Self-assembled microspherical aggregates that work as whispering gallery mode (WGM) optical resonators are synthesized from a novel hygroscopic polymer covalently appended with an aggregation-induced emission luminogen. The resultant microspheres can absorb moisture from the surrounding atmosphere. Accordingly, the WGM resonant peaks shift due to t...

The manipulation of dual fluorescence behavior in aggregation-induced emission enhancement (AIEE) of a tetraphenylethene (TPE)-appended polymer by optical tweezers was investigated herein. Optical tweezers using a focused near-infrared continuous-wave laser...

Interconversion of atropisomers of chiral 3,3’‐di‐tert‐butyl‐9,9’‐bicarbazole linked by a single N−N bond was analyzed by DFT calculations and experiments. The calculations revealed that the trans transition state has a lower energy for the interconversion than the cis transition state. The lowest transition state of interconversion between natural...

Elastic organic crystals have attracted considerable attention as next‐generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10‐dibromoanthracene are ela...

As a new element for electric-field driven molecular memory, we developed a hexaarylbenzene derivative in which three difluorophenyl groups and three aryl groups as a dipolar rotor and a rotation suppressor, respectively, are alternately substituted to the central benzene core. This molecule has two rotational isomeric forms, both of which preserve...

The anisotropic Poisson effect of an elastic 9,10‐dibromoanthracene single crystal was observed. The macroscopic anisotropic Poisson effect is well consistent with microscopic anisotropic Poisson effect in the level of molecular packing structure that was simulated by DFT calculations. Its bending and stretching deformation‐induced fluorescence cha...

The structure and substitution pattern of the side chains of polymers affect polymer-chain behaviors in solution and physical properties in the solid state. As a part of our studies on...

We present spatiotemporal control of aggregation‐induced emission enhancement (AIEE) of a protonated tetraphenylethene derivative by optical manipulation. A single submicrometer‐sized aggregate is initially confined by laser irradiation when its fluorescence is hardly detectable. The continuous irradiation of the formed aggregate leads to sudden an...

Ein fokussierter Laserstrahl fängt ein einzelnes Aggregat eines protonierten Tetraphenylethen-Derivats ab. Dessen molekulare Struktur lässt sich manipulieren, indem die Abstoßungskräfte zwischen den Molekülen ausgeschaltet werden, was die aggregationsinduzierte Emissionsverstärkung (AIEE) aktiviert. Die hellgelbe Fluoreszenz des Aggregats kann über...

Upright orientation of a molecular adsorbate is one of the most practical keys for controlling surface functionalities by using self-assembled monolayers. However, lateral interactions between the upright molecules become more complex than planar molecules since they are not confined in a single plane. Here a scanning tunnelling microscope (STM) wa...

In this study, ultralow 1/f noise organic thin-film transistors (OTFTs) based on parylene gate dielectrics modified with triptycene (Trip) modifiers were fabricated. The fabricated OTFTs showed the lowest 1/f noise level among those of previously reported OTFTs. It is well known that 1/f noise causes degradation of signal integrity in analog and di...

A recently developed diazacyclooctane-containing ladder polymer, which represents the first example of a ladder polymer with a large degree of conformational freedom, undergoes coordination and elimination of a Lewis acid...

We present a highly ordered surface modification layer for polymers based on ambient solution-processed triptycene (Trip) derivatives for high-mobility organic thin-film transistors (OTFTs). The nested packing of Trip molecules results in the formation of 2D hexagonal arrays, which stack one-dimensionally on the surface of polymer dielectrics witho...

When employing self-assembled monolayer (SAM) for tuning surface- and interface-properties, organic molecules that enable strong binding to the substrate, large-area structural uniformity, precise alignment of functional groups, and control of their density are highly desirable. To achieve these goals, tripod systems bearing multiple bonding sites...

Through a first-principles theoretical study, thiol tripods with a rigid C 3 -symmetric triptycene are proposed as excellent building blocks to achieve well-defined molecule-metal contact. We designed two types of tripods, where three thiol groups are connected to the triptycene skeleton either directly (1) or via a methylene bridge (2), whose geom...

We report a simple and facile procedure to control molecular orientation in a single-molecule junction and relevant rectification properties. Rectification properties of single-molecule junctions consisting of tripodal triptycene and C 60 moieties at the termini that couple to the Au electrodes were determined using the break junction method. Becau...

Here we report the facile derivatization of a cyano-substituted stilbene into higher π-extended analogues. The cyano-substituted stilbene, which serves as a synthetic scaffold, has a bromo group and a formyl group on its 4- and 4′-position of the phenylene rings and thus readily undergoes selective transformation into other functional groups using...

A surprising terminal-group effect on the structural and physical properties of an amorphous polymer is reported. We recently demonstrated that triptycene derivatives with substituents at the 1,8,13-positions show specific self-assembly behavior, enabling the formation of a well-defined “2D + 1D” structure based on nested hexagonal packing of the t...

We recently reported that tetraphenylethene-appended poly(acrylic acid) derivatives (e.g., PAA-TPE0.02) can serve as fluorescent Ca²⁺ sensors in the presence of physiological concentrations of biologically relevant ions, amino acids, and sugars. However, in the presence of basic proteins such as albumins, the Ca²⁺-sensing property of the polymer is...

In organic electronics the functionalization of dielectric substrates with self-assembled monolayers is regarded as an effective surface modification strategy that may significantly improve the resulting device performance. However, this technique is not suitable for polymer substrates typically used in flexible electronics. Here, we report organic...

To assemble functional molecular units into a desired structure while controlling positional and orientational order is a key technology for the development of high-performance organic materials that exhibit electronic, optoelectronic, biological and even dynamic functions. For this purpose, we cannot rely simply on the inherent self-assembly prope...

Unlike planar aromatic compounds, bowl-shaped sumanene, which has concave and convex faces with different electrostatic potentials, tends to form a one-dimensional columnar assembly without causing slip-stacking in the crystal. Here we report the first successful synthesis of liquid-crystalline (LC) sumanenes, which was brought about by the incorpo...

Effective induction of preferred-handed helicity of polyacetylenes by the pendant mechanically chiral rotaxanes is discussed. Polyacetylenes possessing optically active mechanically chiral rotaxanes in the side chains were synthesized by the polymerization of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepared via the threading...

Effective induction of preferred-handed helicity of polyacetylenes by the pendant mechanically chiral rotaxanes is discussed. Polyacetylenes possessing optically active mechanically chiral rotaxanes in the side chains were synthesized by the polymerization of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepared via the threading...

We recently reported that tetraphenylethene-appended poly(acrylic acid) derivatives [PAA-TPEx (x = 0.01–0.05)] provide a fluorescent Ca²⁺ sensor, where aggregation-induced emission (AIE) of the TPE pendants occurs in conjunction with Ca²⁺-triggered polymer-chain folding. On the basis of dynamic and static light-scattering data, here we discuss the...

2,3,5,6,8,9-hexabromosumanene (2) with Br groups at all the peripheral aromatic carbons was successfully synthesized. Single-crystal X-ray structural analysis of 2 revealed the formation of a one-dimensional columnar structure in the solid state, where the molecules overlapped in an eclipsed manner. The SuzukiMiyaura cross-coupling of 2 and various...

The synthesis of ladder polymers is still a big challenge in polymer chemistry, and in particular, there are few examples of conformationally flexible well-defined ladder polymers. Here we report an efficient and convenient route to conformationally flexible ladder polymers, which is based on a postpolymerization reaction of a rigid ladder polymer...

1-Methoxy-8-(diphenylphosphino)triptycene (1), featuring high structural rigidity and steric bulkiness around the phosphine functionality, was synthesized as a new chiral monophosphine ligand for transition metal-catalyzed reactions. In the presence of 5–10 mol ppm (i.e., 0.0005–0.001 mol %) Pd(OAc)2 and 1 (2 equiv for Pd), Suzuki–Miyaura cross-cou...

Organic dielectric materials that can respond to electric fields have drawn much attention because of their potential applications to memory and sensing devices. One of the essential requirements for organic dielectric materials is the ability of changing the overall dipole moment in response to external electric fields. In this context, sumanene d...

Porous polymers offer great advantages compared to other microporous materials in terms of solubility and processability. However, the design of porous polymers has suffered from the limited availability of suitable building blocks. Here we propose a conceptually new strategy for the design of porous polymers, which involves the transformation of a...

A free-standing membrane that consists of a newly synthesized spirobiindane-based microporous polymer carrying trimethylammonium hydroxide groups exhibited a good OH⁻ conductivity of 65 mS cm⁻¹ at 80 °C under 100% relative humidity, which demonstrates its potential for use in solid-state alkaline fuel cells.

Tailoring structurally anisotropic molecular assemblies while controlling their orientation on solid substrates is an important subject for advanced technologies that use organic thin films. Here we report a supramolecular scaffold based on tripodal triptycene assemblies, which enables functional molecular units to assemble into a highly oriented,...

Oligomeric o-phenylenes are an emerging class of helical molecules that exhibit complex conformational behaviour, which is determined by their terminal groups and the solvent environment. Using scanning tunnelling microscopy (STM), we investigated the conformational behaviour of octameric o-phenylenes (OP8s) featuring Br or NO2 terminal groups (OP8...