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Coordination variation by solvent environment change leading to various yttrium-based MOFs with flexible ligands.

A new oxo-bridged chromium-molybdenum heterometallic complex, O-CrMoHC ([Cr4(MoO4)2O2(OAc)4(DMF)4]·2DMF), was synthesized by using a simple solvothermal reaction. In this complex, the octahedrally coordinated Cr(III) and tetrahedrally coordinated Mo(VI) metal centers are bridged by oxo ligands. O-CrMoHC has in-plane π-conjugation systems, which are interconnected by noncoordinating DMF molecules. The crystals show anisotropic conductivity with respect to the crystal planes, and theoretical calculations were used to study their origins. The O-CrMoHC single crystals exhibited that a relatively high electrical conductivity with an average value of 5.37 × 10-7 S/cm was observed along the [01-1] direction, but the current level was very low along the [100] direction. This is the first report of anisotropic conductivity observed in the single crystal of a monomeric heterometallic complex.

We demonstrated the synthesis of a conductive two-dimensional metal-organic framework (MOF) thin film by single-step all-vapor-phase chemical vapor deposition (CVD). The synthesized large-area thin film of Cu

Carrier doping in conductive radical crystal systems is one of the most important and challenging issues in employing radicals as charge carriers, i.e., electronic radicals for high-performance organic electronics. Here, we report an experimental demonstration of the increase in the radical population and the corresponding increase in electrical conductivity by water desorption-involved crystal structure change upon mild heating. The electrical conductivity of the dihydrophenazinium radical cation (H₂PNZ·⁺) crystal is enhanced by 4 orders of magnitude with an increase in radical population by 1.5 times according to the electron paramagnetic resonance signal after heating at 333 K. Single-crystal X-ray analyses show that the increase in radical population originates from the phase transformation from dimer-like radical units to monomer-like radical units upon mild heating in a narrow temperature range. The increase in intermolecular distance results in producing more independent radicals and reducing the band gap. Therefore, the electrical conductivity is increased by the synergistic effects of the radical population increase and band gap reduction.

Producing more than one structure from the same set of metal and ligand precursors will grant structural diversity in metal-organic framework (MOF) systems. One of the biggest obstacles of getting structural diversity for the late transition metals is that the coordination mode is pretty much fixed by nature. Herein, we show that two different coordination modes to Cu(II) are possible for flexible ligands containing hydrophilic terminal groups through solvent guidance. It is demonstrated that trans,trans-muconic acid (H2muco) ligands coordinate to Cu(II) to form Cu(II) muconate MOFs having a 1D chain structure and a 2D plane structure in water-rich and DMF-rich water-DMF mixed solvent systems, respectively. It is suggested that the interaction between ligands and solvent is responsible for the selective coordination. A similar result was observed from the attempts using the fumaric acid ligand. Our results provide a new direction to obtain diverse secondary building units for the construction of diverse MOFs.

Chiral supramolecular metal–organic frameworks (SMOFs), i.e., AlaNDI-Ca micro-/nanocrystals have been synthesized via solvothermal reaction using alanine-based naphthalene diimide (NDI) ligands and calcium nitrate. Interestingly, chiral self-discrimination is observed upon mixing two enantiomeric ligands with calcium nitrate due to the thermodynamic preference of heterochiral SMOFs over homochiral analogs. Upon irradiation with UV light, the conductivity of SMOFs micro-/nanocrystals significantly increases and their color changes from yellow to dark brown, due to the electron-transfer-related chemical processes inside the SMOF and/or photo-induced radical formation in NDI ligands, while they are not responsive to visible light. Heterochiral AlaNDI-Ca micro-/nanocrystals with a large band gap exhibit excellent photoswitching properties, due to the reversible generation and depletion of radicals upon exposure to UV light or in the dark, respectively. To our knowledge, photodetecting MOFs for optoelectronics are extremely rare, and herein we have firstly quantitatively characterized single crystalline SMOF photodiodes with redox NDI ligands with regard to their visible-blind UV photodetecting properties with high photoresponsivity and detectivity, which exhibit superior performances in comparison with precedent MOF-based photodetectors. These findings pave the way for applications of multifunctional micro-/nanoscaled MOFs in next-generation optoelectronics.

The impurities in commercial pentacene products prohibit systematic and accurate studies on pentacene. We report that highly pure pentacene crystals can be obtained in high yield by using a physical vapor transport process with hydrogen (H2) carrier gas. While other popular carrier gases including argon and nitrogen gas result in dihydropentacene–pentacene cocrystals as a major product, only H2 carrier gas results in pure pentacene crystals. This happens by effectively suppressing the disproportionation reaction of pentacene, which largely owes to its reaction with dihydropentacene, a popular impurity in pentacene. The efficient formation of highly pure pentacene crystals directly from commercial raw precursors will contribute to systematic studies on pentacene as well as development of novel strategies for the growth of high purity organic semiconducting materials.

A kinetic overgrowth allowing organic molecular crystals in various morphologies is induced by temperature-dependent viscosity change of crystallization solution. By this strategy, concave cube and octapod fullerene C70 crystals were successfully obtained by antisolvent crystallization (ASC). The structural analysis of fullerene C70 crystals indicates that the morphological difference is the result of kinetic processes, which reveals that viscosity, the only variable that can change dynamics of solutes, has a significant influence on determining the morphology of crystals. The effect of solvent viscosity in the stage of crystal growth was investigated through time-dependent control experiments, which led to the proposal of a diffusion rate-based mechanism. Our findings suggest morphology control of organic crystals by diffusion rate control, which is scarcely known compared to inorganic crystals. This strategic method will promote the morphology controls of various organic molecular crystals, and boost the morphology–property relationship study.

Solid-state conversion by the spontaneous redox reaction between tetrathiafulvalene (TTF) and ferric ion is employed to obtain morphology-retained TTF mixed valence (MV) salt crystals. Radical spec...

Chiral organic optoelectronics using circularly polarized light (CPL) as the key element in the photonic signal has recently emerged as a next-generation photonic technology. However, it remains challenging to simultaneously achieve high polarization selectivity and superior optoelectronic performance. Supramolecular two-dimensional (2D) chiral organic single crystals may be good candidates for this purpose due to their defect-free nature, molecular diversity, and morphologies. Here, quasi-2D single crystals of chiral perylene diimides with parallelogram and triangle/hexagon morphologies have been selectively fabricated

Summary Poor solubility of π-conjugated two-dimensional polymers (C2Ps) has been a significant roadblock in incorporating these emergent materials into electronic devices by simple solution processing. Here, we report a rational design of triphenylene-based building blocks that condense via a series of reversible reactions for self-error-correction and a final irreversible fixation to form a pyrazine motif, which leads to the formation of crystalline C2Ps in solution without any aid of template or preorganization. Unlike typical covalent organic frameworks, remarkably, these materials remain dispersed as single- to few-layer films in solution, presumably because of protonation of pyrazine motifs by the strong acid employed in the synthesis. The C2Ps can be easily drop-cast onto solid surfaces for characterization and fabrication of electronic devices. The thin polymer films display a long-range internal order and exhibit high hole mobility up to 4 cm2V−1s−1, the highest among C2Ps, which paves the way to design high-performance optoelectronic devices.

Together with high conductivity, high flexibility is an important property required for next generation organic electronic components. Both properties are difficult to achieve together especially when the components are crystalline because of the intrinsic high brittleness of organic molecular crystals. We report an organic radical crystal system that has both high flexibility and high conductivity. The crystal consists of 9,10-bis(phenylethynyl)anthracene radical cation (BPEA.+ ) units, and shows flexibility under pressure with high conductivity in ambient condition exhibiting average conductivity of 2.68 S cm-1 when normal linear shape, as well as 2.43 S cm-1 when bent. The structural analysis reveals that both a short π-π distance (3.290 A) between BPEA.+ units that are aligned along the crystal length direction, and the presence of PF6 - counter ions induce flexibility and high electrical conductivity.

TTF

A new oxo-bridged chromium-molybdenum heterometallic complex, O-CrMoHC ([Cr

Titanyl phthalocyanine (TiOPc) single crystals have received significant attention due to the remarkable mobility of charge carriers with excellent air stability and phase-dependent electrical properties. One of the biggest obstacles is their polymorphism behavior during crystal growth, which hinders the formation of desired crystals. Herein, we have attempted the selective polymorphism control of titanyl phthalocyanine (TiOPc) single crystals using the physical vapor transport (PVT) technique. Subsequently, the selective growth of the α-, β-, C-phase of TiOPc crystals can be successfully achieved depending on different types of substrates. The polymorphism control of the TiOPc crystals was found to be affected by interfacial energy variation through molecule–substrate interactions so that the unique molecular packing of TiOPc crystals is determined by the kind of substrate. Notably, it is reported for the first time that the C-phase of the TiOPc crystal has a rectangular tube-shaped morphology. Interestingly, it exhibits no PL emission as compared to that of the α- or β-phase crystals, indicating the dominant non-radiative relaxation of excitons. Accordingly, it shows much higher photoconductivity as compared to those of the α- and β-phases. These results provide an in-depth understanding of the crystal growth of phthalocyanines, particularly in view of polymorph control, and open up other possibilities for their practical applications in photoelectronic devices.

Chiral self-sorting has great potential for constructing new complex structures and determining chirality-dependent properties in multicomponent mixtures. However, it is still of great challenge to achieve high fidelity chiral self-discrimination. Besides, the researches on the coordination polymers or metal-organic frameworks for micro/nanooptoelectronics are still rare due to their low conductivity and difficulty in developing a rapid and simple scale-up synthetic method. Here, heterochiral supramolecular coordination networks (SCNs) were synthesized by the solvothermal reaction of naphthalene diimide enantiomers and cadmium iodide, using the chirality as a synthetic tuning parameter to control the morphologies. Intriguingly, heterochiral micro/nanocrystals exhibited photochromic and photodetecting properties. Furthermore, we also developed a simple and efficient doping method to enhance the conductivity and photoresponsivity of micro/nanocrystals using hydrazine. From experimental and theoretical studies, the mechanism was suggested as follows: the radicals in the singly occupied molecular orbital level of the ligands provide charge carriers that can undergo "through-space" transport between π-π stacked ligands and the electron transfer from adsorbed hydrazine to the SCNs results in reduction of energy gap, leading to increased conductivity. Our findings demonstrate a simple and powerful strategy for implementing coordination networks with redox ligands for micro/nanooptoelectronic applications.

Electrically conducting cation-charged dihydrophenazinium radical (H2PNZ•+) crystals were formed by a one-pot photoreaction. Furthermore, new secondary crystals were grown directly from the H2PNZ•+ crystal surface through a surface-mediated recrystallization (SMR) process by a secondary photoreaction with water. Depending on the absence or presence of light during the exposure of the H2PNZ•+ single crystal to water, neutral yellow PNZ crystals (SMRY) or densely packed green H2PNZ•+ crystals (SMRG) were formed, respectively, on the surface of the mother H2PNZ•+ crystal. The single-crystal X-ray analysis reveals that the newly obtained SMRG radical crystal exhibits a shorter intercolumnar distance than the original H2PNZ•+ crystal, resulting in increased electrical conductivity.

Yttrium-based MOFs with different coordination numbers (CNs) of yttrium ions were synthesized from the same precursor. The 7-coordinated yttrium-based MOF exhibits an infinite 3D structure, while the 9-coordinated yttrium-based MOF shows a 2D layer stacked structure. Control experiments showed that the concentration of the ligand determines the CN and eventually the geometric structures.

The role of antisolvent molecular geometry on the determination of the final molecular crystals morphology formed by the reverse antisolvent crystallization (r-ASC) process has been unveiled. Herein, we newly report that the rod-, disk-, and cube-shaped tetra(4-aminophenyl)porphyrin molecular crystals were selectively obtained by employing o-, m-, and p-xylene as an antisolvent during r-ASC process with ethanol employed as a good solvent. The X-ray diffraction results of the crystals provide a clear indication about the correlation between the solute–solvent interactions and the resulting crystal morphologies. The results show that the geometry of xylene has a pivotal effect on the crystal growth direction and morphologies, especially for polyhedrons. This finding would provide opportunities not only for realization of quite rare organic polyhedral crystals but also for in-depth studies about the fundamental crystallization process.

Morphology-retained solid-state photoconversion of anthracene (AN) to 9,10-anthraquinone (PC-ANQ) and dipara-anthracene (PC-DPA) was accomplished by irradiating mercury lamp light to plate-shaped AN single crystal in oxygen and argon atmosphere, respectively. The photoconverted crystals retained the original plate shape morphology of the starting AN crystal, whereas the emission profile and crystal structure were significantly changed. The electrical conductivity of PC-ANQ crystal is 5 orders of magnitude greater than that of the starting AN crystal, whereas the PC-DPA crystal exhibits a decreased conductivity. The AN/PC-ANQ/PC-DPA heterostructures with smooth interface were successfully obtained by inducing the photoconversion only at the desired area.

In this paper, we report an efficient alkali metal doping system for organic single crystals. Our system employs an enhanced diffusion method for the introduction of alkali metal into organic single crystals by controlling the sample temperature to induce secondary thermal activation. Using this system, we achieved intercalation of potassium into picene single crystals with closed packed crystal structures. Using optical microscopy and Raman spectroscopy, we confirmed that the resulting samples were uniformly doped and became K2picene single crystal, while only parts of the crystal are doped and transformed into K2picene without secondary thermal activation. Moreover, using a customized electrical measurement system, the insulator-to-semiconductor transition of picene single crystals upon doping was confirmed by in situ electrical conductivity and ex situ temperature-dependent resistivity measurements. X-ray diffraction studies showed that potassium atoms were intercalated between molecular layers of picene, and doped samples did not show any KH- nor KOH-related peaks, indicating that picene molecules are retained without structural decomposition. During recent decades, tremendous efforts have been exerted to develop high-performance organic semiconductors and superconductors, whereas as little attention has been devoted to doped organic crystals. Our method will enable efficient alkali metal doping of organic crystals and will be a resource for future systematic studies on the electrical property changes of these organic crystals upon doping.

The multistate redox-active/multi-interactive ligand 5,5',8,8'-tetra(4-pyridyl)-2,2'-(1,4-phenylene)bis-1H-perimidine (H2 TPP) was designed and synthesized. H2 TPP undergoes four one-electron oxidation steps, and was used for the preparation of a multistate redox-active coordination network in a solid-liquid interface reaction using molten Cd2+ salts. The multiple redox states of H2 TPP were confirmed spectroscopically by stepwise four-electron oxidation. Spectroscopic analysis indicated that the mixed-valence states of the ligand are class II on the UV/Vis/NIR timescale and borderline class II/class III on the ESR timescale.

A core–shell drop-drying (CSDD) method that employs spontaneous formation of a droplet-in-droplet system was newly presented for the efficient formation of molecular crystals. Well-defined methylene blue crystals were successfully obtained from the core–shell droplet with a significantly diminished coffee-ring effect.

Summary In recent years, there has been a rapid increase in the abuse of amphetamine-type stimulants (ATS). One way to tackle this problem is to develop an easy, sensitive, rapid, and cheap ATS detection platform. Here, a strategy that synergistically combines the selectivity of supramolecular chemistry and the sensitivity of organic field-effect transistors is used as the basis of an ATS sensor. Cucurbit[7]uril derivatives that can selectively detect ATS have been synthesized and used as a functional material. The fabricated amperometric sensors exhibited unprecedented sensitivity toward ATS, with a detection limit of nanomolar concentrations in urine and picomolar concentrations in water or a physiologic buffer. The feasibility of this strategy was further demonstrated through the preparation of flexible and wearable devices with a wireless sensing platform. This sensing system offers rapid and sensitive detection of trace amounts of ATS in urine and other samples at the point of use.

By changing the rate of evaporation, two kinds of crystalline films composed of redox-active porous coordination networks (1 and 2) were selectively prepared on a gold-patterned substrate using a DMF solution of 2,5,8-tri(4-pyridyl)1,3-diazaphenalene and Cd(NO3)2. We found the highly sensitive humidity sensing ability of film 1. Single crystal structures and infrared spectroscopic analyses before and after hydration of a single crystal of 1 revealed the sensing mechanism: exchange of nitrate ions with water on Cd atoms occurred in hydrated conditions to generate a conductive cationic network.

Alkali metal doping is an essential process for developing organic superconductors. The conventional vapor-phase alkali metal doping, however, frequently suffers from low efficiency and poor reproducibility mainly due to the inhomogeneous reaction between alkali metal vapor and target organic molecule powder. To overcome this issue, here we developed a facile and highly reproducible solution-phase alkali metal doping (SPD) and successfully applied it to prepare potassium-doped fullerene (K3C60) superconductors. Different from the conventional vapor-phase alkali metal doping, the SPD method resulted in almost perfect diamagnetism with an unprecedented high shielding fraction (∼99.5%) with high reproducibility (>80%). It works well with popular commercially available solvents, like ammonia solution in THF, methylamine solution in THF, and even pure THF at room temperature. We believe that our highly facile and efficient SPD approach will be a great help for the finding of next-generation organic superconductors, especially searching for high-Tc organic superconductors.

We demonstrate an effective and facile method for the deposition of gold nanoparticles (AuNPs) on graphene by using spontaneous galvanic reaction. Despite the interest and importance of the hybrid structure of noble metal-deposited graphene has been considerably increased for its fundamental knowledge in chemical and physical sciences and for its various applications, the progress of this subject is very slow mainly because of the lack of synthetic methods for such structures, especially that are not free from chemical contamination and usage of complex and expensive equipment. Therefore, we developed a new method allowing chemically pure AuNPs/graphene hybrid structures employing galvanic reaction. The spontaneous galvanic reaction was derived from reductant/graphene/oxidant sandwich structures, such as Au ions/graphene/Ge wafer and Au ions/graphene/copper foil, by placing Au ion solution droplets on graphene transferred on a germanium wafer or as made graphene on Cu foil, respectively. According to scanning electron microscopy and atomic force microscopy results, it was confirmed that AuNPs were successfully formed on the graphene surface. This result implies two important points. One is that the formation of pure AuNPs on graphene is possible without using other chemicals frequently required for conventional NP preparation. The other one is that it was experimentally demonstrated that there are electronic communications between the oxidant and reductant that are separated by graphene, through which electrons can pass freely.

A redox-active molecule, 2,5,8-tri(4-pyridyl)-1,3-diazaphenalene (TPDAP), was synthesized by four-step reactions. The two-step redox reaction was revealed by solid-state cyclic voltammetry. The cry...

Synthesis of morphologically well-defined crystals of metalloporphyrin by direct crystallization based on conventional anti-solvent crystallization method without using any additives has been rarely reported. Herein, we demonstrate an unconventional and additive-free synthetic method named reverse anti-solvent crystallization method to achieve well-defined zinc-porphyrin cube crystals by reversing the order of the addition of solvents. The extended first solvation shell effect mechanism is therefore suggested to support the synthetic process by providing a novel kinetic route for reaching the local supersaturation environment depending on the order of addition of solvents, which turned out to be critical to achieve clean cube morphology of the crystal. We believe that our work not only extends fundamental knowledge about the kinetic process in binary solvent systems, but also enables great opportunities for shape-directing crystallization of various organic and organometallic compounds.

Cucurbit[7]uril (CB[7]) is known to bind strongly to hydrophilic amino saccharide guests with exceptional α-anomer selectivities under aqueous conditions. Single-crystal X-ray crystallography and computational methods were used to elucidate the reason behind this interesting phenomenon. The crystal structures of protonated galactosamine (GalN) and glucosamine (GluN) complexes confirm the inclusion of α anomers inside CB[7] and disclose the details of the host-guest binding. Whereas computed gas-phase structures agree with these crystal structures, gas-phase binding free energies show preferences for the β-anomer complexes over their α counterparts, in striking contrast to the experimental results under aqueous conditions. However, when the solvation effect is considered, the binding structures drastically change and the preference for the α anomers is recovered. The α anomers also tend to bind more tightly and leave less space in the CB[7] cavity toward inclusion of only one water molecule, whereas loosely bound β anomers leave more space toward accommodating two water molecules, with markedly different hydrogen-bonding natures. Surprisingly, entropy seems to contribute significantly to both anomeric discrimination and binding. This suggests that of all the driving factors for the strong complexation of the hydrophilic amino saccharide guests, water mediation plays a crucial role in the anomer discrimination.

To minimize the leakage of microwave which can occur when one pulls the door of a microwave oven during its operation, shape optimization of the door frame is presented. A numerical optimization is implemented to minimize the dynamic twisting deformation of the door frame. Shape design variables are defined, which represent the dimension of the bead in the flange. Two optimal design problems are established to minimize the maximum twisting deformation from harmonic response analysis. The problems are solved, their results being compared and evaluated.