Yoshihito Honsho

Light-Harvesting Conjugated Microporous Polymers: Rapid and Highly Efficient Flow of Light Energy with a Porous Polyphenylene Framework as Antenna

The molecular design of light-harvesting antennae requires not only the segregation of a large number of chromophore units in a confined nanospace but also the cooperation of these units in achieving highly efficient energy transduction. This article describes the synthesis and functions of a polyphenylene-based conjugated microporous polymer (PP-CMP). PP-CMP was recently designed and synthesized by Suzuki polycondensation reaction and used as an antenna for the noncovalent construction of a light-harvesting system. In contrast to linear polyphenylene, PP-CMP consists of conjugated three-dimensional polyphenylene scaffolds and holds inherent porous structure with uniform pore size (1.56 nm) and large surface area (1083 m(2) g(-1)). It emits blue photoluminescence, is capable of excitation energy migration over the framework, and enables rapid transportation of charge carrier with intrinsic mobility as high as 0.04 cm(2) V(-1) s(-1). The microporous structure of PP-CMP allows for the spatial confinement of energy-accepting coumarin 6 molecules in the pores and makes the high-throughput synthesis of light-harvesting systems with designable donor-acceptor compositions possible. Excitation of the PP-CMP skeleton leads to brilliant green emission from coumarin 6, with an intensity 21-fold as high as that upon direct excitation of coumarin 6 itself, while the fluorescence from PP-CMP itself is wholly quenched as a result of energy transfer from the light-harvesting PP-CMP framework to coumarin 6. The PP-CMP skeleton is highly cooperative, with an average of 176 phenylene units working together to channel the excitation energy to one coumarin 6 molecule, and features the energy-transfer process with quick, efficient, and vectorial character. These unique characteristics clearly originate from the conjugated porous structure and demonstrate the usefulness of CMPs in the exploration of pi-electronic functions, in addition to their gas adsorption properties thus far reported.

Synthesis of Metallophthalocyanine Covalent Organic Frameworks That Exhibit High Carrier Mobility and Photoconductivity

Covalent organic frameworks (COFs) are a new class of porous architectures that allow the integration of organic units with atomic precision into long-range-ordered twoand three-dimensional structures. 2] From a synthetic point of view, COFs are intriguing as they allow a new degree of control of porosity, composition, and component positions. As high-surface-area materials that link elements of low atomic mass by covalent bonds, COFs exhibit considerable potential for gas adsorption applications. As the first report on COFs in 2005, several families of COFs have been reported. However, the construction of COFs has to date been limited to certain monomers, and the lack of suitable procedures that utilize other units has impeded further advances in this emerging field. To advance this field it is therefore important to extend the limited number of synthetic methods and monomer units available. Phthalocyanines are large, planar p-electronic macrocycles with broad absorption profiles that could serve as intriguing units in the construction of porous frameworks. Crystalline phthalocyanine metal–organic frameworks have been shown to be useful in applications such as gas adsorption owing to their extended porous structures. However, phthalocyanine-based porous covalent polymers are usually amorphous and disordered. The combination of phthalocyanine units into a well-defined covalent framework thus remains an undeveloped area of research, offering great potential for obtaining novel functionality depending on the particular alignment and stacking. The eclipsed stacking endows arene-based COFs with unique functionality, such as excimer emission, exciton migration, and photoresponse. Herein, we have developed a new phthalocyanine unit for the synthesis of nickel phthalocyanine-based COFs (NiPc COF; Scheme 1). The compound, based on (2,3,9,10,16,17,23,24octahydroxyphthalocyaninato)nickel(II), [(OH)8PcNi], which has four catechol pairs at peripheral phenyl rings of a phthalocyanine macrocycle. These 2D COFs provide preorganized conduction paths based on precise ordering of the phthalocyanine stack and are ideal for charge carrier transport. Herein we present the high-throughput synthesis and unique properties of the two-dimensional metallophthalocyanine-based COF. The NiPc COF was synthesized by the boronate esterification reaction of [(OH)8PcNi] and 1,4-benzenediboronic acid (BDBA) in dimethylacetamide (DMAc)/o-dichlorobenzene under solvothermal conditions (Scheme 1a). [(OH)8PcNi] has low solubility in common organic solvents owing to its large p system and highly planar structure; typical procedures for the esterification reaction does not lead to the formation of desirable crystalline COFs. With reference to a well-established solvent combination (mesitylene/dioxane) for the synthesis of boronate-linked 2D COFs, 4] we investigated the reaction using different pairs of aromatic solvents (mesitylene, toluene, and o-dichlorobenzene) with hydrophilic solvents (dioxane, dimethylformamide (DMF), and dimethylacetamide (DMAc)). Combinations and results for the esterification reaction are summarized in the Supporting Information, Figure S1. The optimal combination for the preparation of the COFs was found to be o-dichlorobenzene and DMAc. Furthermore, the ratio of o-dichlorobenzene to DMAc was varied from 1:1 to 1:9 (vol/vol) to investigate the effect on crystallinity, as monitored by powder X-ray diffraction (PXRD) measurements. A mixture of o-dichlorobenzene/DMAc (1:2 vol/vol) gave the best result, as indicated by the intensity of the PXRD signals (Supporting Information, Figure S1). The NiPc COF was synthesized as a dark green powder in 90 % yield. It is notable that this method gives a yield that is much higher than the previously reported value (48%). Fourier-transform infrared (FTIR) spectra of the NiPc COF exhibited characteristic bands that are due to the boronate ester at 1053, 1089, 1291, and 1347 cm , and a typical C=N stretch at 1480 cm 1 for the phthalocyanine units (Supporting Information, Figure S2, Table S1). Solid-state H–C CP/MAS NMR spectroscopy using a 920 MHz H NMR spectrometer at a MAS rate of 15 kHz and a [*] X. Ding, Dr. J. Guo, X. Feng, Dr. P. Maitarad, Prof. Dr. D. Jiang Department of Materials Molecular Science Institute for Molecular Science 5-1 Higashiyama, Myodaiji, Okazaki 444-8787 (Japan) Fax: (+ 81)564-59-5520 E-mail: jiang@ims.ac.jp

Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds

Covalent organic frameworks are a class of crystalline organic porous materials that can utilize π–π-stacking interactions as a driving force for the crystallization of polygonal sheets to form layered frameworks and ordered pores. However, typical examples are chemically unstable and lack intrasheet π-conjugation, thereby significantly limiting their applications. Here we report a chemically stable, electronically conjugated organic framework with topologically designed wire frameworks and open nanochannels, in which the π conjugation-spans the two-dimensional sheets. Our framework permits inborn periodic ordering of conjugated chains in all three dimensions and exhibits a striking combination of properties: chemical stability, extended π-delocalization, ability to host guest molecules and hole mobility. We show that the π-conjugated organic framework is useful for high on-off ratio photoswitches and photovoltaic cells. Therefore, this strategy may constitute a step towards realizing ordered semiconducting porous materials for innovations based on two-dimensionally extended π systems.

An n-Channel Two-Dimensional Covalent Organic Framework

Co-condensation of metallophthalocyanine with an electron-deficient benzothiadiazole (BTDA) block leads to the formation of a two-dimensional covalent organic framework (2D-NiPc-BTDA COF) that assumes a belt shape and consists of AA stacking of 2D polymer sheets. Integration of BTDA blocks at the edges of a tetragonal metallophthalocyanine COF causes drastic changes in the carrier-transport mode and a switch from a hole-transporting skeleton to an electron-transporting framework. 2D-NiPc-BTDA COF exhibits broad and enhanced absorbance up to 1000 nm, shows panchromatic photoconductivity, is highly sensitive to near-infrared photons, and has excellent electron mobility as high as 0.6 cm(2) V(-1) s(-1).

High-Rate Charge-Carrier Transport in Porphyrin Covalent Organic Frameworks: Switching from Hole to Electron to Ambipolar Conduction†

Well conducted: a two-dimensional porphyrin covalent organic framework is described. Owing to the eclipsed stacking alignment, the framework is conductive and allows high-rate carrier transport through the porphyrin columns. The central metal in the porphyrin rings changes the conducting nature of the material from hole to electron, and to ambipolar conduction. It also drives the high on-off ratio photoconductivity of the framework.

An Ambipolar Conducting Covalent Organic Framework with Self-Sorted and Periodic Electron Donor-Acceptor Ordering

Covalent organic frameworks (COFs) are crystalline polygons with permanent porosity that have potential application in gas adsorption and storage. [ 1–14 ] π -Electronic versions have also been prepared, by integrating aromatic building blocks into the polygon skeletons. [ 15–25 ] The unusual two-dimensional (2D) conformation endows the frameworks with crystallized layer structures, which could set π -components in face-to-face stacked columns and provide aligned conduction pathways. [ 19–27 ] It is highly interesting and remains a challenge if the unique 2D COF architecture can be explored for the construction of highly aligned donor (D) and acceptor (A) systems. The crystallization of electron donors (D) and acceptors (A) into macroscopic heterojunctions with segregated D and A

Block-copolymer-nanowires with nanosized domain segregation and high charge mobilities as stacked p/n heterojunction arrays for repeatable photocurrent switching.

Development of materials for efficient photoenergy conversion is a subject of critical importance in current science and technology. Efficient performance requires well-controlled segregation of electron donor and acceptor moieties, which we have achieved using block copolymers of tetraphenylporphinatozinc(II) (donor) and C(60) fullerene (acceptor) using living ring-opening metathesis polymerization (ROMP). The resulting amphiphilic ROMP block copolymers undergo self-assembly into nanostructured phase-segregated 1-dimensional nanowires with an approximately 5.5 nm periodicity zebra-stripe-like morphology simply by drop-casting solutions of the polymers onto a substrate such as mica or highly oriented pyrolytic graphite (HOPG). Thin films of the self-assembled nanophase-segregated copolymers exhibit high charge carrier mobilities (approximately 0.26 cm(2) V(-1) s(-1)) and electrical conductivities (up to 6.4 x 10(-4) cm(2) V(-1) s(-1)) as well as highly repeatable photocurrent switching with rapid ON/OFF responses upon white light irradiation.

A Self-Threading Polythiophene: Defect-Free Insulated Molecular Wires Endowed with Long Effective Conjugation Length

Herein, we report on a self-threading polythiophene whose conjugated molecular wire is sheathed within its own cyclic side chains. The defect-free insulating layer prevents electronic cross-communication between the adjacent polythiophene backbone even in the solid film. Notably, the covalently linked cyclic side chains extend the effective conjugation length of the interior polythiophene backbone, which results in an excellent intrawire hole mobility of 0.9 cm(2) V(-1) s(-1).

Noncovalently netted, photoconductive sheets with extremely high carrier mobility and conduction anisotropy from triphenylene-fused metal trigon conjugates.

Supramolecular assembly of small molecules via noncovalent interaction is useful for bottom-up construction of well-defined macroscopic structures. This approach is attracting increasing interest due to its high potential in manufacturing novel molecular electronic and optoelectronic devices. This Article describes the synthesis and functions of a sheet-shaped assembly from novel triphenylene-fused metal trigon conjugates. These conjugates were recently designed and synthesized by a divergent method and used for the supramolecular self-assembly of sheet-like objects. In contrast to triphenylene, which absorbs photons in ultraviolet region, the triphenylene-fused metal trigon conjugate shows a strong absorption band in the visible region. The metal trigon conjugate emits green photoluminescence with significantly enhanced quantum yield and allows intramolecular energy migration, as a result of extended pi-conjugation over metal sites. It assembles via physical gelation to form noncovalent sheets that collect a wide wavelength range of photons from ultraviolet to visible regions. The noncovalent sheets allow exciton migration and are semiconducting with an extremely large intrinsic carrier mobility of 3.3 cm(2) V(-1) s(-1). They are highly photoconductive, produce photocurrent with a quick response to light irradiation, and are capable of repetitive on-off switching. Moreover, these sheets facilitate a conduction path perpendicular to the sheet plane, thus exhibiting a spatially distinctive anisotropy in conduction. The noncovalent sheet assemblies with these unique characteristics are important for molecular optoelectronic devices based on solution-processed soft materials.

Electron- or hole-transporting nature selected by side-chain-directed π-stacking geometry: liquid crystalline fused metalloporphyrin dimers.

Novel liquid crystalline (LC) semiconductors were prepared from the copper complex of a fused porphyrin dimer as the electroactive core by attaching to its periphery dodecyl and semifluoroalkyl side chains site-specifically (P≡P(hetero)) and semifluoroalkyl side chains alone (P≡P(homo)). The former and latter formed rectangular columnar and orthorhombic LC mesophases, respectively, where the stacking geometries of the π-conjugated core are quite different from one another. Although the π-electronic properties of the core units in P≡P(hetero) and P≡P(homo) in solution are substantially identical to one another, transient photocurrent profiles of their LC states under time-of-flight conditions clearly showed that P≡P(hetero) behaves as an n-type semiconductor, whereas P≡P(homo), in contrast, behaves as a p-type semiconductor.