Porphyrin Nanocrystal Synthesized via Chemical Reaction Route: pH-Sensitive Reversible Transformation between Nanocrystals and Bulk Single Crystal

Crystalline nanostructures with octahedral morphology have been prepared by self-assembling of cationic porphyrin (H₆TPyP)⁴⁺·4Cl^– produced through chemical reaction route in aqueous solution depending on the synergistic interactions among hydrogen-bonding, π–π stacking, and ion pairing. Unexpectedly, the gradual decrease in pH by the slow evaporation of solvent in the nano-octahedron aqueous suspension obtained in situ led to the selective etching of the original nanocrystal and the isolation of (H₆TPyP)⁴⁺·4Cl^– bulk single crystals in the last stage. More interestingly, the increase in pH by adding water again into this bulk single-crystal-containing system led to the regeneration of nano-octahedrons, indicating the reversible transformation between porphyrin nano-octahedrons and bulk single crystals triggered by pH. Mechanistic investigations through powder and single-crystal X-ray diffraction analyses together with the electron microscopic, in particular, HRTEM, clearly reveal that the unique surface effect and anisotropic character of the nanomaterials differing from the bulk organic materials are responsible for such pH-sensitive reversible transformation of the two crystalline materials by controlling the dissolution or aggregation of (H₆TPyP)⁴⁺·4Cl^–, which actually induces the reversible formation and breaking of the (pyridine)­N⁺–H···Cl^–···H–O­(H₂O)···H–N⁺(pyridine) hydrogen bonds among cationic porphyrin building blocks at different pH. This result, to control the crystallinity and the unprecedented reversible transformation between nanocrystal and bulk single crystals just by tuning the pH of the synthesis process, as well as the use of the peculiar nanoeffect such as surface effect to adjust the self-assembling process, provides useful a tool for the controllable synthesis of crystalline materials and is expected to be helpful for further research and application of organic nanomaterials

Porphyrin Nanocrystal Synthesized via Chemical Reaction Route: pH-Sensitive Reversible Transformation between Nanocrystals and Bulk Single Crystal

Crystalline nanostructures with octahedral morphology have been prepared by self-assembling of cationic porphyrin (H₆TPyP)⁴⁺·4Cl^– produced through chemical reaction route in aqueous solution depending on the synergistic interactions among hydrogen-bonding, π–π stacking, and ion pairing. Unexpectedly, the gradual decrease in pH by the slow evaporation of solvent in the nano-octahedron aqueous suspension obtained in situ led to the selective etching of the original nanocrystal and the isolation of (H₆TPyP)⁴⁺·4Cl^– bulk single crystals in the last stage. More interestingly, the increase in pH by adding water again into this bulk single-crystal-containing system led to the regeneration of nano-octahedrons, indicating the reversible transformation between porphyrin nano-octahedrons and bulk single crystals triggered by pH. Mechanistic investigations through powder and single-crystal X-ray diffraction analyses together with the electron microscopic, in particular, HRTEM, clearly reveal that the unique surface effect and anisotropic character of the nanomaterials differing from the bulk organic materials are responsible for such pH-sensitive reversible transformation of the two crystalline materials by controlling the dissolution or aggregation of (H₆TPyP)⁴⁺·4Cl^–, which actually induces the reversible formation and breaking of the (pyridine)­N⁺–H···Cl^–···H–O­(H₂O)···H–N⁺(pyridine) hydrogen bonds among cationic porphyrin building blocks at different pH. This result, to control the crystallinity and the unprecedented reversible transformation between nanocrystal and bulk single crystals just by tuning the pH of the synthesis process, as well as the use of the peculiar nanoeffect such as surface effect to adjust the self-assembling process, provides useful a tool for the controllable synthesis of crystalline materials and is expected to be helpful for further research and application of organic nanomaterials

(Pc)Eu(Pc)Eu[<i>trans</i>-T(COOCH₃)₂PP]/GO Hybrid Film-Based Nonenzymatic H₂O₂ Electrochemical Sensor with Excellent Performance

A facile approach was developed for preparing the multilayer hybrid films of mixed (phthalocyaninato) (porphyrinato) europium­(III) triple-decker compound (Pc)­Eu­(Pc)­Eu­[<i>trans</i>-T­(COOCH₃)₂PP] (<b>1</b>) and graphene oxide (GO) using the solution-processing QLS method. The combination of the nature of relatively high conductivity and great surface area for GO with the electroactive and semiconductive triple-decker compound in ITO electrode renders the hybrid film excellent sensing property for H₂O₂, due to the optimized triple-decker molecular packing in the uniform-sized nanoparticles (ca. 70 nm) formed on the GO surface. The amperometric responses are linearly proportional to the concentration of H₂O₂ in the range of 0.05–1800 μM with a fast response time of 0.03 s μM^–1, a low detection limit of 0.017 μM, and good sensitivity of 7.4 μA mM^–1. The present work represents the best result of tetrapyrrole-based nonenzymatic electrochemical sensor for H₂O₂. Nevertheless, the triple-decker/GO/ITO also shows excellent stability, reproducibility, and selectivity, indicating the great potential of electroactive tetrapyrrole rare earth sandwich compounds in combination with GO in the field of nonenzymatic electrochemical sensors

(TFPP)Eu[Pc(OPh)₈]Eu[Pc(OPh)₈]/CuPc Two-Component Bilayer Heterojunction-Based Organic Transistors with High Ambipolar Performance

Organic thin film transistor (OTFT) devices fabricated by the solution-based QLS technique from a mixed (phthalocyaninato)­(porphyrinato) europium complex (TFPP)­Eu­[Pc­(OPh)₈]­Eu­[Pc­(OPh)₈] exhibit air-stable ambipolar performance with mobilities of 6.0 × 10^–5 cm² V⁻¹ s⁻1 for holes and 1.4 × 10^–4 cm² V^–1 s^–1 for electrons, respectively. In good contrast, the two-component bilayer heterojunction thin film devices constructed by directly growing (TFPP)­Eu­[Pc­(OPh)₈]­Eu­[Pc­(OPh)₈] on vacuum deposited (VCD) CuPc film using solution based QLS method were revealed to show unprecedented ambipolar performance with carrier mobilities of 0.16 cm² V^–1 s^–1 for holes and 0.30 cm² V^–1 s^–1 for electrons. In addition to the intrinsic role of p-type organic semiconductor, the VCD CuPc film on the substrate also acts as a good template that induces significant improvement over the molecular ordering of triple-decker compound in the film. In particular, it results in the change in the aggregation mode of (TFPP)­Eu­[Pc­(OPh)₈]­Eu­[Pc­(OPh)₈] from J-type in the single-layer film to H-type in the bilayer film according to the UV–vis, XRD, and AFM observations

Amphiphilic (Phthalocyaninato) (Porphyrinato) Europium Triple-Decker Nanoribbons with Air-Stable Ambipolar OFET Performance

An amphiphilic mixed (phthalocyaninato) (porphyrinato) europium­(III) triple-decker complex [Pc­(OPh)₈]­Eu­[Pc­(OPh)₈]­Eu­[TP­(CCCOOH)­PP] (<b>1</b>) with potential ambipolar semiconducting HOMO and LUMO energy levels has been designed, synthesized, and characterized. The OFET devices fabricated by quasi-Langmuir-Shäfer (QLS) technique at the air/water interface with nanoparticle morphology display hole mobility of 7.0 × 10^–7 cm² V^–1 s^–1 and electron mobility of 7.5 × 10^–7 cm² V^–1 s^–1, which reflects its ambipolar semiconducting nature. However, the performance of the devices fabricated via a “phase-transfer” method from <i>n</i>-hexane with one-dimensional nanoribbon morphology was significantly improved by 3–6 orders of magnitude in terms of hole and electron mobilities, 0.11 and 4 × 10^–4 cm² V^–1 s^–1, due to the enhanced π–π interaction in the direction perpendicular to the tetrapyrrole rings associated with the formation of a dimeric supramolecular structure building block depending on the intermolecular hydrogen bonding between the neighboring triple-decker molecules in the one-dimensional nanoribbons

Hierarchically Structured Porous Nitrogen-Doped Carbon for Highly Selective CO₂ Capture

Nitrogen-doping has proven to be an effective strategy for enhancing the CO₂ adsorption capacity of carbon-based adsorbents. However, it remains challenging to achieve a high doping level of nitrogen (N) and a significant porosity in a carbon material simultaneously. Here we report a facile method that enables the fabrication of ordered macroporous nitrogen-doped carbon with the content of N as high as 31.06 wt %. Specifically, we used poly­(EGDMA-<i>co</i>-MAA) microspheres as a template to fabricate the structure which can strongly interact with melamine (the precursor of nitrogen-doped carbon framework), self-assemble into three-dimensionally ordered structure, and be easily removed afterward. Upon chemical activation, significant microporosity is generated in this material without degrading its ordered macroporous structure, giving rise to a hierarchically structured porous nitrogen-doped carbon in which a remarkable N content (14.45 wt %) is retained. This material exhibits a moderate CO₂ adsorption capacity (2.69 mmol g^–1 at 25 °C and 3.82 mmol g^–1 at 0 °C under 1 bar) and an extraordinarily high CO₂/N₂ selectivity (134), which is determined from the single-component adsorption isotherms based on the ideal adsorption solution theory (IAST) method. This value far exceeds the CO₂/N₂ selectivity of thus-far reported carbon-based adsorbents including various nitrogen-doped ones. We believe that such an unprecedented CO₂/N₂ selectivity is largely associated with the unusually high N content as well as the partially graphitic framework of this material

Controlled Synthesis of Carbon Nanofibers Anchored with Zn_<i>x</i>Co_3–<i>x</i>O₄ Nanocubes as Binder-Free Anode Materials for Lithium-Ion Batteries

The direct growth of complex ternary metal oxides on three-dimensional conductive substrates is highly desirable for improving the electrochemical performance of lithium-ion batteries (LIBs). We herein report a facile and scalable strategy for the preparation of carbon nanofibers (CNFs) anchored with Zn_<i>x</i>Co_3–<i>x</i>O₄ (ZCO) nanocubes, involving a hydrothermal process and thermal treatment. Moreover, the size of the ZCO nanocubes was adjusted by the quantity of urea used in the hydrothermal process. Serving as a binder-free anode material for LIBs, the ZnCo₂O₄/CNFs composite prepared using 1.0 mmol of urea (ZCO/CNFs-10) exhibited excellent electrochemical performance with high reversible capacity, excellent cycling stability, and good rate capability. More specifically, a high reversible capacity of ∼600 mAh g^–1 was obtained at a current density of 0.5 C following 300 charge–discharge cycles. The excellent electrochemical performance could be associated with the controllable size of the ZCO nanocubes and synergistic effects between ZCO and the CNFs

Surface Modification of Methylamine Lead Halide Perovskite with Aliphatic Amine Hydroiodide

By spin-coating method, a thin layer of dodecylamine hydroiodide (DAHI) is introduced to the surface of perovskite CH₃NH₃PbI<i>_x</i>Cl_3–<i>x</i>. This layer of DAHI successfully changes the surface of perovskite from hydrophilic to hydrophobic as revealed by the water contact angle measurement. Significantly enhanced fluorescence intensity and prolonged fluorescence lifetime are found for these modified films in comparison to those of unmodified perovskite films, suggesting that the number of structure defects is reduced dramatically. The compatibility between the perovskite and hole transfer layer (HTL) is also improved, which leads to more efficient hole collection from the perovskite layer by HTL as revealed by the fluorescence spectra, fluorescence decay dynamics, as well as the transient photocurrent measurements. Moreover, the perovskite solar cells (PSCs) fabricated from these modified perovskite films exhibit significantly improved humidity stability as well as promoted photoelectron conversion efficiency (PCE). The result of this research reveals for the first time that the layer of aliphatic amino hydroiodide is a multiple functions layer, which can not only improve the humidity stability but also promote the performance of PSCs by reducing the defect number and improve the compatibility between perovskite and HTL. Because the structure of aliphatic amines can be functionalized with myriad of other groups, this perovskite modification method should be very promising in promoting the performance of PSCs

Employing Singlet Fission into Boosting the Generation of Singlet Oxygen and Superoxide Radicals for Photooxidation Reactions

Developing highly efficient heavy-metal-free photosensitizers (PSs) for the production of reactive oxygen species (ROS) is urgent to achieve wide applications of ROS, yet it remains a great challenge. As a proof of concept, singlet fission (SF), possessing the exciton multiplication ability with a maximum 200% triplet yield, is employed to generate ROS. Herein, a metal-free tetracene dimer with a high yield (∼164%) of long-lived triplets (>300 μs) is prepared and used to generate singlet oxygen (1O2) and superoxide radicals (O2·–). Remarkably, 1O2 and O2·– yields are boosted compared to the existing traditional PSs based on intersystem crossing (ISC). The 1O2 yield reaches an unprecedented ∼148%, representing the highest value ever reported so far. Thus, this SF PS shows an improved photooxidation activity over ISC PSs. Additionally, the 1O2 and O2·– generation mechanisms are described clearly by combining TA spectra and controlled experiments. This represents the first example of utilizing the two triplet states produced by SF to generate ROS and catalyze related reactions. The work not only presents a strategy for generating and enhancing the 1O2/O2·– yield but also opens up a new field for the application of SF

Exploring Hardness and the Distorted sp² Hybridization of B–B Bonds in WB₃

In this work, tungsten triboride (WB₃) was successfully synthesized at high pressure and high temperature. The structure was reconfirmed to be WB₃ (<i>P</i>6₃<i>mmc</i>), and some part has a tungsten atomic defect according to the measurement results of X-ray diffraction, high-resolution transmission electron microscopy, and Rietveld refinement. The asymptotic Vickers hardness that had eliminated influence of excess boron is 25.5 GPa for WB₃. This value is in good agreement with the previous theoretic results. Proof of novel electron transfer between the tungsten atom and the boron atom was found. A deficient amount of transfer electron induces distorted sp² hybridization of B–B bonds in WB₃. The weakly directional sp² hybridization of B–B bonds is an essential factor that can influence the hardness of WB₃. Our results are helpful to design new hard and superhard materials of transition metal borides