Metallated Graphynes as a New Class of Photofunctional 2D Organometallic Nanosheets

Scanning Tunneling Spectroscopy Investigation of Au-bis-acetylide Networks on Au(111): The Influence of Metal-Organic Hybridization

Graphdiyne (GDY) is an appealing two-dimensional carbon material, but the on-surface synthesis of a single layer remains challenging. Demetalation of well-crystalline metal acetylide networks, though in its infancy, provides a new avenue to on-surface synthesized GDY substructures. In spite of the synthetic efforts and theoretical concerns, there are few reports steeped in elaborate characterization of the electronic influence of metalation. In this context, we focused on the surface supported Au-bis-acetylide network, which underwent demetalation after further annealing to form hydrogen-substituted GDY. We made a comprehensive study on the geometric structure and electronic structure and the corresponding demetalized structure on Au(111) through STM, noncontact atomic force microscopy (nc-AFM), scanning tunneling spectroscopy (STS), and density functional theory (DFT) simulations. The bandgap of the Au-bis-acetylide network on Au(111) is measured to be 2.7 eV, while the bandgap of a fully demetalized Au-bis-acetylide network is estimated to be about 4.1 eV. Our findings reveal that the intercalated Au adatoms are positioned closer to the metal surface compared with the organic skeletons, facilitating electronic hybridization between the surface state and unoccupied frontier molecular orbitals of organic components. This leads to an extended conjugation through Au-bis-acetylene bonds, resulting in a reduced bandgap.

Pyrazinacene conjugated polymers: a breakthrough in synthesis and unraveling the conjugation continuum

Pyrazinacenes are next generation N-heteroacenes and represent a novel class of stable n-type materials capable of accepting more than one electron and displaying intriguing features, including prototropism, halochromism, and redox chromism. Astonishingly, despite a century since their discovery, there have been no reports on the conjugated polymers of pyrazinacenes due to unknown substrate scope and lack of pyrazinacene monomers that are conducive to condensation polymerization. Breaking through these challenges, in this work, we report the synthesis of previously undiscovered and highly coveted conjugated polymers of pyrazinacenes. In order to understand the intricacies of conjugation extension within the acene and along the polymer backbone, a series of electronically diverse four pyrazinacene conjugated polymers were synthesized. Polymers synthesis required optimizing a few synthetic steps along the 12-step synthetic pathway. The generated pyrazinacene monomers are not amenable to the popular condensation polymerizations involving Pd or Cu catalysts. Gratifyingly, Pd and Cu free dehydrohalogenation polymerization of the monomer with HgCl2 resulted in high molecular weight organometallic conjugated pyrazinacene polymers within a few minutes at room temperature. The dual role played by the Hg(ii) during the polymerization, combined with the self-coupling of the RHgCl (intermediate), is at the core of successful polymerization. Notably, the self-coupling of intermediates challenges the strict stoichiometric balance typically required for step-growth polymerization and offers a novel synthetic strategy to generate high molecular weight conjugated polymers even with imbalanced monomer stoichiometries. A combination of electrochemical studies and DFT-B3LYP simulations indicated that the presence of the reduced pyrazine ring promotes interacene π-conjugation through the metal center, in contrast to completely oxidized tetrazaazaanthracene. The extension of conjugation results in ca. 2 eV lower reduction potential for polymers compared to the monomer, placing the LUMO energy levels of these polymers on par with some of the best-known n-type polymers. Also, the presence of NH protons in the pyrazinacene polymers show ionochromism and red-shift UV-vis absorption maximum by ca. 100 nm. This work not only shows a way to realize highly desirable and elusive pyrazinacene conjugated polymers but also paves the way for a library of n-type conjugated polymers that can undergo multi-electron reduction.

Coordination Behavior of the Tellurium Incorporated Mercuraazametallamacrocycle and Investigation of d10 ⋅⋅⋅d10 Interactions between Closed Shell (Ag+ Hg2+ ) Metal Ions

Herein, a new tellurium and mercury containing mercuraazametallamacrocycle has been prepared via (2+2) condensation of bis(o-aminophenyl)telluride and bis(o-formylphenyl)mercury(II). The isolated bright yellow solid of mercuraazametallamacrocycle has adopted unsymmetrical figure-of-eight conformation in the crystal structure. To study the metallophilic interactions between closed shell metal ions, the macrocyclic ligand has been treated with two equiv. of AgOTf (OTf=trifluoromethansulfonate) and AgBF4 , which afforded greenish-yellow bimetallic silver complexes. The isolated silver complexes displayed intramolecular Hg⋅⋅⋅Ag, Te⋅⋅⋅Ag interactions as well as intermolecular Hg⋅⋅⋅Hg interactions and formed an extended 1D molecular chain by directing six atoms to interact as TeII ⋅⋅⋅AgI ⋅⋅⋅HgII ⋅⋅⋅HgII ⋅⋅⋅AgI ⋅⋅⋅TeII in a non linear fashion. The Hg⋅⋅⋅Ag, Te⋅⋅⋅Ag interactions have also been studied in solution by 199 Hg, 125 Te NMR spectroscopy, absorption, and emission spectroscopy. In DFT calculations, the Atom in Molecule (AIM) analysis, non-covalent interactions (NCI), natural bonding orbital (NBO) analysis strongly supported for experimental evidences and revealed that the intermolecular Hg⋅⋅⋅Hg interaction is stronger than the intramolecular Hg⋅⋅⋅Ag interactions.

Physical mechanism on the linear spectrum and nonlinear spectrum in a twist bilayer graphdiyne nanodisk

The one-photon absorption properties (OPA), two-photon absorption properties (TPA), electronic circular dichroism (ECD) spectra and partial DOS (PDOS) of a twist bilayer graphdiyne nanodisk (TwBLGDY-ND) were investigated by using a variety of quantum chemistry and wave function analyses. The physical mechanism of the twist bilayer graphdiyne nanodisk (TwBLGDY) with optical properties regulated by twisting angles was revealed. The results show that the twist angle makes the TwBLGDY form a moiré superlattice structure, and electron excitation mainly occurs in the first ring of the moiré superlattice structure. The contribution of atomic orbitals in these fragments to transition dipole moments is greater and electronic transitions are more likely to occur. When the twist angle increases from 0° to 15°, the absorption spectrum of the system is red shifted, which is mainly due to the enhancement of electron excitation characteristics. When the twist angle increases from 15° to 27.5°, the absorption spectrum of the system is blue shifted, due to the enhanced charge transfer within the layer. On the other hand, the twist angle can regulate the TPA absorption cross section of the system to enhance the intensity of the absorption spectrum. The twist angle can also regulate chirality by adjusting the spatial distribution of electric dipole transition and magnetic dipole transition. This study can provide theoretical guidance for constructing chiral optical devices based on the TwBLGDY structure.

Siloxene Nanosheets and Their Hybrid Gel Glasses for Broad-Band Optical Limiting

With the development of laser technology, the research of novel laser protection materials is of great significance. In this work, dispersible siloxene nanosheets (SiNSs) with a thickness of about 1.5 nm are prepared by the top-down topological reaction method. Based on the Z-scan and optical limiting testing under the visible-near IR ranges nanosecond laser, the broad-band nonlinear optical properties of the SiNSs and their hybrid gel glasses are investigated. The results show that the SiNSs have outstanding nonlinear optical properties. Meanwhile, the SiNSs hybrid gel glasses also exhibit high transmittance and excellent optical limiting capabilities. It demonstrates that SiNSs are promising materials for broad-band nonlinear optical limiting and even have potential applications in optoelectronics.

Synthesis, Photoswitching Behavior and Nonlinear Optical Properties of Substituted Tribenzo[a,d,g]coronene

A family of tribenzocoronene derivatives bearing various substituents (3) were constructed through the Diels-Alder reaction, followed by the Scholl oxidation, where the molecular structure of 3b was determined via single crystal X-ray diffraction analysis. The effect of substitution on the optical and electrochemical property was systematically investigated, with the assistance of theoretical calculations. Moreover, the thin films of the resulting molecules 3b and 3e complexed with fullerene produced strong photocurrent response upon irradiation of white light. In addition, 3b and 3e exhibit a positive nonlinear optical response resulting from the two-photon absorption and excited state absorption processes.

A type-II NGyne/GaSe heterostructure with high carrier mobility and tunable electronic properties for photovoltaic application

The two-dimensional heterostructures with type-II band alignment and super-high carrier mobility offer an updated perspective for photovoltaic devices. Here, based on the first-principles calculation, a novel vertical NGyne/GaSe heterostructure with an intrinsic type-II band alignment, super-high carrier mobility (10⁴cm²V^-1s^-1), and strong visible to ultraviolet light absorption (10⁴-10⁵cm^-1) is constructed. We investigate the electronic structure and the interfacial properties of the NGyne/GaSe heterostructure under electric field and strain. The band offsets and band gap of the NGyne/GaSe heterostructure can be regulated under applied vertical electric field and strain efficiently. Further study reveals that the photoelectric conversion efficiency of the NGyne/GaSe heterostructure is vastly improved under a negative electric field and reaches up to 25.09%. Meanwhile, near-free electron states are induced under a large applied electric field, leading to the NGyne/GaSe heterostructure transform from semiconductors to metal. Our results indicate that the NGyne/GaSe heterostructure will have extremely potential in optoelectronic devices, especially solar cells.

Metalloporphyrin-Linked Mercurated Graphynes for Ultrastable CO2 Electroreduction to CO with Nearly 100% Selectivity at a Current Density of 1.2 A cm-2

The electrochemical reduction reaction of carbon dioxide (CO₂RR) to the desired feedstocks with a high faradaic efficiency (FE) and high stability at a high current density is of great importance but challenging owing to its poor electrochemical stability and competition with the hydrogen evolution reaction (HER). Guided by theoretical calculations, herein, a series of novel metalloporphyrin-linked mercurated graphynes (Hg-MTPP) were designed as electrocatalysts for CO₂RR, since the mercurated graphyne blocks induce a high HER overpotential. Notably, Hg-CoTPP was synthesized and produced a maximum CO FE of 95.6% at -0.76 V (vs reversible hydrogen electrode (RHE)) in an H-type cell, and a CO FE of 91.2% even at -1.26 V (vs RHE), due to a great suppression of HER. The Hg-CoTPP combined with N-doped graphene (Hg-CoTPP/NG) was able to achieve a high CO FE of nearly 100% at a current density of 1.2 A cm^-2 and particularly a ground-breaking stability of over 360 h at around 420 mA cm^-2 in a flow-type cell. Further experimental and computational results revealed that the mercurated graphyne of Hg-CoTPP brings a high HER overpotential and tunes the d-band electronic states of the metal center that make the d-band center closer to the Fermi level, thus enhancing the bonding of *COOH intermediates on Hg-CoTPP. The introduction of NG could shorten the Co-N coordination bonds, which enhances electron transfer to the metal center to lower the energy barrier for *COOH. Our results illustrated that Hg-MTPP could serve as a new class of two-dimensional (2D) materials and provide a design concept for developing efficient electrocatalysts for CO₂RR in commercial applications.

Conjugated polymers based on metalla-aromatic building blocks

Conjugated polymers usually require strategies to expand the range of wavelengths absorbed and increase solubility. Developing effective strategies to enhance both properties remains challenging. Herein, we report syntheses of conjugated polymers based on a family of metalla-aromatic building blocks via a polymerization method involving consecutive carbyne shuttling processes. The involvement of metal d orbitals in aromatic systems efficiently reduces band gaps and enriches the electron transition pathways of the chromogenic repeat unit. These enable metalla-aromatic conjugated polymers to exhibit broad and strong ultraviolet–visible (UV–Vis) absorption bands. Bulky ligands on the metal suppress π–π stacking of polymer chains and thus increase solubility. These conjugated polymers show robust stability toward light, heat, water, and air. Kinetic studies using NMR experiments and UV–Vis spectroscopy, coupled with the isolation of well-defined model oligomers, revealed the polymerization mechanism.

Interfacially confined preparation of fumaronitrile-based nanofilms exhibiting broadband saturable absorption properties

Interfacial nanofilms with nonlinear optical (NLO) properties were prepared via confined dynamic condensation of 4,4'-methylenedianiline (MDA) with the synthesized 2,3-bis(4-(bis(4-formylphenyl)amino)phenyl)fumaronitrile (BTFA). Investigated using the open-aperture Z-scan technique, BTFA showed reverse saturable absorption ascribed to the synergetic mechanisms of two-photon and excited-state absorption. In contrast, the as-prepared nanofilms demonstrated broadband saturable absorption within the spectral range of 720∼1700 nm. The characteristics of nonlinear absorption coefficient (β) decreased along with increasing the incident pulse intensity. Taking advantage of the flexibility and post-machinability properties, the folding layers of the nanofilms offered the feasibility to fine-tune the specific NLO responses. The optimal β value was found to be -10.1 cm/MW for eight-layer nanofilm as well as the normalized transmittance increased up to 35-fold at 800 nm. Utilized as a conceptual saturable absorber, the representative modulation depth and saturation intensity were observed to be around 2.4% and 7.37 GW/cm² at 800 nm, respectively, comparable to traditional two-dimensional (2D) materials. Aiming to clarify the possible underlying physical processes, a four-level model was employed to illustrate the fast relaxation of the excited states. Present work demonstrates that proper design of building blocks combined with interfacially confined dynamic condensation enables rational development of high-performance NLO materials.

Computational Insight into Metallated Graphynes as Single Atom Electrocatalysts for Nitrogen Fixation

The electrochemical nitrogen reduction reaction (NRR) is expected to achieve sustainable ammonia synthesis via direct nitrogen fixation; however, the high-quality catalysts that play a crucial role in the NRR are still lacking. The emerging transition metal-1,3,5-triethynylbenzene (TM-TEB) frameworks offer attractive possibilities in the electrochemical catalysis due to the featured atomic and electronic structures. This work presents a comprehensive first-principles study of the TM-TEB systems for TMs from the first three d-block series and systematically explores their potential applications as NRR electrocatalysts. By designing a hierarchical screening strategy, the TM-TEB systems are evaluated based on the NRR catalytic activity as well as the competition from the hydrogen evolution reaction. In addition, in order to have a deeper understanding of the catalytic activities of the TM-TEB systems, diverse possible NRR paths on the TM-TEB surfaces are completely analyzed as well. Our analysis reveals that the TM-TEB systems with TM = V, Mo, Tc, W, and Os are electrocatalysts with a high NRR catalytic activity, while among them, only Mo- and V-TEB show promising NRR selectively. This work demonstrates the great potential of the TM-TEB systems as electrocatalysts in the NRR process, which improves the understanding of the TM-TEB systems and can motivate further exploration of their application in catalysis.

Passively Q-switched Tm:YAP laser with a tantalum aluminum carbide saturable absorber

Tantalum aluminum carbide (Ta₄AlC₃) phase ceramic (MAX) material has attracted much attention because of its high conductivity, high strength, corrosion resistance, and good optical properties. However, there are too few reports on lasers with Ta₄AlC₃-based saturable absorbers (SAs). We prepared and characterized a Ta₄AlC₃-based SA whose nonlinear absorption performances were achieved at a 2 µm waveband range and which was used in a passively Q-switched (PQS) Tm:YAP laser. In the PQS mode, a maximum average output power of 0.78 W was achieved with the central output wavelength of 1991.86 nm from a PQS Tm:YAP laser, corresponding to a pulse duration of 926 ns at 143.8 kHz.

Switching the Nonlinear Optical Absorption of Titanium Carbide MXene by Modulation of the Surface Terminations

Surface terminations of two-dimensional materials should have a strong influence on the nonlinear optical (NLO) properties, but the relationship between surface terminations and NLO properties has not yet been reported. In this work, switching the NLO properties of MXenes (Ti₃C₂T_x) via "surface terminations modulation" is explored. The surface terminations of Ti₃C₂T_x are modulated by electrochemical treatment, resulting in different states (viz., Ti₃C₂T_x(pristine), Ti₃C₂T_x(═O rich), and Ti₃C₂T_x(-OH rich)). The sign and magnitude of the effective NLO absorption coefficient (β_eff) change with the surface terminations. Ti₃C₂T_x(═O rich) shows a relatively large saturable absorption (SA) with laser excitation at 515 nm (β_eff = -1020 ± 136.2 cm GW^-1), while reverse saturable absorption (RSA) is found in Ti₃C₂T_x(pristine) and Ti₃C₂T_x(-OH rich). The RSA of Ti₃C₂T_x(pristine) and Ti₃C₂T_x(-OH rich) is attributed to excited-state absorption, while the SA of Ti₃C₂T_x(═O rich) is associated with Pauli blocking. With laser excitation at 800 nm, the β_eff of Ti₃C₂T_x(-OH rich) is 113 ± 3.2 cm GW^-1, 1.68 times that of Ti₃C₂T_x(pristine); the RSA is caused by photon-induced absorption. Our results reveal a correlation between surface terminations and NLO properties, highlighting the potential of MXenes in photoelectronics.

A sextuple-decker heteroleptic phthalocyanine heterometallic samarium-cadmium complex with crystal structure and nonlinear optical properties in solution and gel glass

A sextuple-decker heteroleptic phthalocyanine heterometallic compound (1) with a subunit arrangement of {(Pc)Sm(Pc)Cd(Pc*)Cd(Pc*)Cd(Pc)Sm(Pc)} has been prepared and analyzed using various spectroscopic instruments, in which four unsubstituted phthalocyanine anions (Pc) and two substituted analogues (Pc*) with n-pentoxyl substituents at eight peripheral positions are connected through the complexation of two Sm(III) and three Cd(II) ions. In particular, its sextuple-decker structure has been disclosed by the single-crystal X-ray diffraction technique. The solution and gel glass forms of this compound display third-order nonlinear optical properties due to the intrinsic conjugated nature over the sextuple-decker sandwich complex.

Creating supramolecular semiregular Archimedean tilings via gas-mediated deprotonation of a terminal alkyne derivative

Combining surface-confined reactions with supramolecular self-assembly allows the chemical transformation of simple molecular precursors into higher-level tectons to generate complex tessellations with unique structural and functional properties.