Two-Dimensional Metal-Polyphthalocyanine Conjugated Porous Frameworks as Promising Optical Limiting Materials

The activity origin of two-dimensional MN4-contained periodical macrocyclic structures towards electro-catalytic hydrogen evolution

The two-dimensional MN4-contained periodical macrocyclic structures (2D MN4/PMCs) have been extensively explored as single atom catalysts through both experimental and theoretical approaches. However, there still lacks deep understanding on the effect of the outer coordination environment in determining the catalytic activity of the inner MN4 center. Combining the density functional theory (DFT) calculations and machine learning (ML) algorithm, we computationally unraveled the origin of electro-catalytic activity of five kinds of 2D MN4/PMCs towards hydrogen evolution reaction (HER). With hydrogen adsorption free energy (ΔGH*) as the indicator for HER catalytic activity, the IrPpor and RhPPpz are screened out as superior HER electrocatalysts based on the DFT calculations. Furthermore, ML studies generated the universal descriptor Φ that highly depends on charge assigned on the metal center (q) and the d-band center of central metal (εd), which is reversely proportional to ΔGH*. The dependence of q and εd on the structural parameters of MN4/PMCs is further unraveled, demonstrating how the outer framework determines catalytic activity of 2D MN4/PMCs.

Synthesis of a Triangle-Fused Six-Pointed Star and Its Electrocatalytic CO2 Reduction Activity

As electrocatalysts, molecular catalysts with large aromatic systems (such as terpyridine, porphyrin, or phthalocyanine) have been widely applied in the CO2 reduction reaction (CO2RR). However, these monomeric catalysts tend to aggregate due to strong π-π interactions, resulting in limited accessibility of the active site. In light of these challenges, we present a novel strategy of active site isolation for enhancing the CO2RR. Six Ru(Tpy)2 were integrated into the skeleton of a metallo-organic supramolecule by stepwise self-assembly in order to form a rhombus-fused six-pointed star R1 with active site isolation. The turnover frequency (TOF) of R1 was as high as 10.73 s-1 at -0.6 V versus reversible hydrogen electrode (vs RHE), which is the best reported value so far at the same potential to our knowledge. Furthermore, by increasing the connector density on R1's skeleton, a more stable triangle-fused six-pointed star T1 was successfully synthesized. T1 exhibits exceptional stability up to 126 h at -0.4 V vs RHE and excellent TOF values of CO. The strategy of active site isolation and connector density increment significantly enhanced the catalytic activity by increasing the exposure of the active site. This work provides a starting point for the design of molecular catalysts and facilitates the development of a new generation of catalysts with a high catalytic performance.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs

Bimetallic metal-organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

Harnessing Nickel Phthalocyanine-Based Electrochemical CNT Sponges for Ammonia Synthesis from Nitrate in Contaminated Water

Electrochemical reduction of nitrate to ammonia is of great interest in water treatment with regard to the conversion of contaminants to value-added products, which requires the development of advanced electrodes to achieve high selectivity, stability, and Faradaic efficiency (FE). Herein, nickel phthalocyanine was homogeneously doped into the fiber of a carbon nanotube (CNT) sponge, enabling the production of an electrode with high electrochemical double-layer capacitance (C_DL) and a large electrochemically active surface area (ECSA). The as-prepared NiPc-CNT sponge could achieve 97.6% nitrate removal, 88.4% ammonia selectivity, and 86.8% FE at a nitrate concentration of 50 mg-N L^-1 under an optimized potential of -1.2 V (vs Ag/AgCl). Meanwhile, the ammonia selectivity could be further improved at the high nitrate concentration. Density functional theory calculations showed that the exposure of Ni-N₄ active sites could effectively suppress the hydrogen evolution reaction and dinitrogen generation, enhancing the ammonia selectivity and Faradaic efficiency. Overall, this work sheds light on the conversion of nitrate to ammonia on the metal phthalocyanine-based electrode, offering a novel strategy for managing nitrate in wastewater.

Preparation of Polyphenylene Ring Derivative Dyes with Wide Wave Absorption Properties and Their Performance Study

Some conjugated benzene ring molecules were prepared using the Sonogashira reaction, and the molecules were post-functionally modified using click chemistry. The optical and electrical band gaps were measured using UV-VIS absorption spectroscopy and the three-electrode method, and the results of both were verified against each other to prove the accuracy of the characterization. In addition, the optical performances of the material were studied by z-scan; almost all materials exhibited good nonlinear optical properties and interconversion between saturable and anti-saturable absorption due to the invocation of click reagents.

Nonlinear Optical Properties of Pyrene Derivatives Based on a Donor-Acceptor Structure and Its Polyurethane Composites

Two pyrenyl Schiff base derivatives with π conjugated structures (B2 and B3) were designed and synthesized. Then, B2 and B3 were added into polyurethane to obtain doped and bonded polyurethane nonlinear optical materials (B2/PU and B3/PU), respectively. The synthesized B2, B3, and polyurethane nonlinear optical materials were tested by a nanosecond (ns) and picosecond (ps) pulse Z-scan at a 532 nm wavelength. Due to the two-photon absorption-induced excited state absorption (TPA-ESA), B2, B3, and polyurethane nonlinear optical materials show reverse saturable absorption (RSA). From a quantum chemistry calculation, it can be concluded that the RSA of B2 and B3 comes from the large π conjugated system and intramolecular charge transfer. Furthermore, B2, B3, and the polyurethane nonlinear optical materials show good optical limiting. B2/PU and B3/PU not only have excellent nonlinear optical properties but also have good transmittance, thermal stability, and processability of polyurethane materials. The combination of pyrenyl Schiff base derivatives and polyurethane materials greatly improves the application of nonlinear small molecules in the field of optical limiting and all-optical switching.

Three-Photon-Induced Singlet Excited-State Absorption for the Tunable Ultrafast Optical-Limiting in Distyrylbenzene: A First-Principles Study

The ground and first singlet excited state absorption in distyrylbenzene(DSB) are simulated based on the linear-response time dependent density functional theory(LR-TDDFT). It is found that distyrylbenzene shows strong reverse saturable...

Heterometallic Al6Zn12 nano-plate with π-conjugated ligand: synthesis and nonlinear absorption properties

Presented herein is the synthesis, structure, and optical properties of the aluminum(III)-zinc(II) heterometallic compound AlOC-57. This compound was found to form a large unit cell (approximately sixteen thousand atoms) and a three-shell nano-plate structure. Based on the Z-scan patterns, the third-order nonlinear optical response of the heterometallic nano-plate was mainly attributed to its nonlinear absorption (reverse saturable absorption).

Third-Order Nonlinear Optical Behavior of an Amide-Tricarboxylate Zinc(II) Metal-Organic Framework with Two-Fold 3D+3D Interpenetration

A new metal-organic framework (MOF), [Zn₄(μ₄-O)(μ₆-L)₂(H₂O)₂]_n·nDMF (ZSTU-10), was assembled from zinc(II) nitrate and N,N',N″-bis(4-carboxylate)trimesicamide linkers and fully characterized. Its crystal structure discloses an intricate two-fold 3D+3D interpenetrated MOF driven by the [Zn₄(μ₄-O)]-based tetragonal secondary building units and the C3-symmetric tris-amide-tricarboxylate linkers (μ₆-L^3-). Topological analysis of ZSTU-10 reveals two interpenetrated 3,6-connected nets with an rtl (rutile) topology. Z-Scan analysis at 532 nm was conducted to study a nonlinear optical (NLO) behavior of ZSTU-10. The nonlinear responses of ZSTU-10 were explored under various laser intensities, revealing notable third-order NLO properties in the visible region. A large two-photon absorption at lower incident intensities highlights the fact that ZSTU-10 can be applied in optical limiting devices as well as optical modulators. Moreover, a nonlinear refractive index (n₂) is indicative of a self-defocusing behavior. This work thus expands a family of novel MOF materials with remarkable optical properties.