Xuesong Ding

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

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).

Pore surface engineering in covalent organic frameworks

Covalent organic frameworks (COFs) are a class of important porous materials that allow atomically precise integration of building blocks to achieve pre-designable pore size and geometry; however, pore surface engineering in COFs remains challenging. Here we introduce pore surface engineering to COF chemistry, which allows the controlled functionalization of COF pore walls with organic groups. This functionalization is made possible by the use of azide-appended building blocks for the synthesis of COFs with walls to which a designable content of azide units is anchored. The azide units can then undergo a quantitative click reaction with alkynes to produce pore surfaces with desired groups and preferred densities. The diversity of click reactions performed shows that the protocol is compatible with the development of various specific surfaces in COFs. Therefore, this methodology constitutes a step in the pore surface engineering of COFs to realize pre-designed compositions, components and functions.

Charge Dynamics in A Donor–Acceptor Covalent Organic Framework with Periodically Ordered Bicontinuous Heterojunctions

The donor–acceptor heterojunction is a key structure in current technologies, including transistors, light-emitting diodes, and photovoltaics, because it controls the charge dynamics in the devices. Covalent organic frameworks (COFs) are crystalline molecular skeletons that allow atomically precise integration of building blocks into periodic array structures. In this regard, we have demonstrated arene, porphyrin, and phthalocyanine COFs that provide periodically ordered columnar arrays of p-components and show outstanding semiconducting and photoconductive properties. We recently synthesized a donor–acceptor COF that gives rise to a periodically ordered bicontinuous heterojunction structure and self-sorted donor and acceptor columnar arrays separated at nanometer-scale intervals. This nanoscopic segregation morphology forms a broad interface for charge separation, provides ambipolar pathways for charge collection, and would be ideal for the current semiconducting devices that involve photoenergy transformations; however, the charge dynamics, which is a key mechanism that controls the energy transformation, remains unclear. Here, we report the charge dynamics of a donor–acceptor COF, which were determined using time-resolved spectroscopy to elucidate the photochemical processes of the free charges from their generation to delocalization and retention. In the COF, the heterojunctions allow an ultrafast electron transfer from the donor to the acceptor columns. Consequently, the light absorption is directly coupled with charge dissociation to generate free charges in the donor and acceptor p-columns within 2 ps. On the other hand, the stacked p-columns delocalize the charges, suppress charge recombination, and retain the charges for a prolonged period of time. We show that both solvated and solid-state COFs enable rapid charge separation and exceptional long-term charge retention, thereby providing a key mechanistic basis to envisage the high potential of donor–acceptor COFs for photoelectric applications. The donor–acceptor COF (Scheme 1a, DZnPc-ANDI-COF) is a tetragonal, mesoporous 2D framework that is composed of zinc phthalocyanine as an electron donor and naphthalene diimide as an acceptor. In the COF, the two p-units are alternately linked within an electron-transfer distance and at a dihedral angle of approximately 428. The COF provides selfsorted, bicontinuous columnar arrays and constitutes periodically structured heterojunctions in which each donor column is interfaced with four acceptor columns that are equally active in capturing photo-generated electrons (Scheme 1b). The DZnPc-ANDI-COF absorbs light over a broad visible and near-infrared region up to 1100 nm (Figure S1 in the Supporting Information). Elemental analysis, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron microscopy confirmed the formation of the COF (Figure S2–S4 and Table S1). The same COF has been reported as a thin film. The DZnPc-ANDI-COF exhibited a type IV nitrogen sorption curve that is characteristic of mesoporous frameworks (Figure 1a). The Brunauer–Emmett–Teller surface area and pore volume were calculated as 1410 mg 1 and 1.25 cmg , respectively. The pore-size distribution profile with a range up

Metallophthalocyanine‐Based Conjugated Microporous Polymers as Highly Efficient Photosensitizers for Singlet Oxygen Generation

Singlet oxygen ((1) O2 ) is of great interest because of its potential applications in photodynamic therapy, photooxidation of toxic molecules, and photochemical synthesis. Herein, we report novel metallophthalocyanine (MPc) based conjugated microporous polymers (MPc-CMPs) as photosensitizers for the generation of (1) O2 . The rigid microporous structure efficiently improves the exposure of the majority of the MPc units to oxygen. The MPc-CMPs also exhibit an enhanced light-harvesting capability in the far-red region through their extended π-conjugation systems. Their microporous structure and excellent absorption capability for long-wavelength photons result in the MPc-CMPs showing high efficiency for (1) O2 generation upon irradiation with 700 nm light, as evident by using 1,3-diphenylisobenzofuran as an (1) O2 trap. These results indicate that MPc-CMPs can be considered as promising photosensitizers for the generation of (1) O2 .

Conducting metallophthalocyanine 2D covalent organic frameworks: the role of central metals in controlling π-electronic functions

Phthalocyanine covalent organic frameworks with different central metals are synthesized, and the AA-stacking structure of the 2D polymer sheets results in periodic phthalocyanine π-columns. The central metals control the π-electronic functions, including the improvement of light absorbance, the ease of carrier transport, and the photocurrent gain.

A Photoresponsive Smart Covalent Organic Framework

Ordered π-columnar structures found in covalent organic frameworks (COFs) render them attractive as smart materials. However, external-stimuli-responsive COFs have not been explored. Here we report the design and synthesis of a photoresponsive COF with anthracene units as the photoresponsive π-building blocks. The COF is switchable upon photoirradiation to yield a concavo-convex polygon skeleton through the interlayer [4π+4π] cycloaddition of anthracene units stacked in the π-columns. This cycloaddition reaction is thermally reversible; heating resets the anthracene layers and regenerates the COF. These external-stimuli-induced structural transformations are accompanied by profound changes in properties, including gas adsorption, π-electronic function, and luminescence. The results suggest that COFs are useful for designing smart porous materials with properties that are controllable by external stimuli.

An Azine‐Linked Covalent Organic Framework: Synthesis, Characterization and Efficient Gas Storage

A azine-linked covalent organic framework, COF-JLU2, was designed and synthesized by condensation of hydrazine hydrate and 1,3,5-triformylphloroglucinol under solvothermal conditions for the first time. The new covalent organic framework material combines permanent micropores, high crystallinity, good thermal and chemical stability, and abundant heteroatom activated sites in the skeleton. COF-JLU2 possesses a moderate BET surface area of over 410 m(2)  g(-1) with a pore volume of 0.56 cm(3)  g(-1) . Specifically, COF-JLU2 displays remarkable carbon dioxide uptake (up to 217 mg g(-1) ) and methane uptake (38 mg g(-1) ) at 273 K and 1 bar, as well as high CO2 /N2 (77) selectivity. Furthermore, we further highlight that it exhibits a higher hydrogen storage capacity (16 mg g(-1) ) than those of reported COFs at 77 K and 1 bar.

Triarylboron-Linked Conjugated Microporous Polymers: Sensing and Removal of Fluoride Ions.

A luminescent conjugated microporous polymer (BCMP-3) has been synthesized in high yield by a carbon-carbon coupling reaction using triarylboron as a building unit. BCMP-3 was fully characterized by using powder X-ray diffraction analysis, Fourier transform infrared spectroscopy, (13) C solid-state NMR spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, and nitrogen and carbon dioxide adsorption. The new three-dimensional conjugated framework possess a high Brunauer-Emmett-Teller (BET) specific surface area up to 950 m(2)  g(-1) with a pore volume of 0.768 cm(3)  g(-1) , good stability, and abundant boron sites in the skeleton. Under excited-light irradiation, BCMP-3 exhibits strong fluorescent emission at 488 nm with a high absolute quantum yield of 18 % in the solid state. Polymer BCMP-3 acts as a colorimetric and fluorescent chemosensor with high sensitivity and selectivity for F(-) over other common anions. In addition, the polymer also works as an adsorbent for F(-) removal and shows good adsorption capacities of up to 24 mg g(-1) at equilibrium F(-) concentrations of 16 mg L(-1) and a temperature of 298 K. The adsorption kinetics and isotherm were analyzed by fitting experimental data with pseudo-second-order kinetics and Langmuir equations. Furthermore, we highlight that BCMP-3 is an adsorbent for fluoride removal that can be efficiently reused many times without loss of adsorption efficiency.

Porous Azo‐Bridged Porphyrin–Phthalocyanine Network with High Iodine Capture Capability

We report a highly efficient iodine adsorbent achieved by rational design of a porous azo-bridged porphyrin-phthalocyanine network (AzoPPN), which was synthesized by a catalyst-free coupling reaction between free-base 5,10,15,20-tetrakis(4-nitrophenyl)-porphyrin and nickel tetraaminophthlocyanine. AzoPPN has a permanent porous structure and plenty of porphyrin and phthalocyanine units in the skeleton as effective sorption sites. It displays excellent adsorption of iodine vapor up to 290 wt. % and also shows remarkable capability as adsorbent for iodine in solution. This strategy of combining physisorption with chemisorption in one adsorbent will pave the way for the development of new materials for iodine capture.