Chemically Driven Interfacial Coupling in Charge-Transfer Mediated Functional Superstructures

Organic Cocrystals: Recent Advances and Perspectives for Electronic and Magnetic Applications

Cocrystal engineering is an advanced supramolecular strategy that has attracted a lot of research interest. Many studies on cocrystals in various application fields have been reported, with a particular focus on the optoelectronics field. However, few articles have combined and summarized the electronic and magnetic properties of cocrystals. In this review, we first introduce the growth methods that serve as the basis for realizing the different properties of cocrystals. Thereafter, we present an overview of cocrystal applications in electronic and magnetic fields. Some functional devices based on cocrystals are also introduced. We hope that this review will provide researchers with a more comprehensive understanding of the latest progress and prospects of cocrystals in electronic and magnetic fields.

Ag(I)-Hived Fullerene Microcube as an Enhanced Catalytic Substrate for the Reduction of 4-Nitrophenol and the Photodegradation of Orange G Dye

We report a facile approach to fabricate an Ag-embedded fullerene (C₆₀) catalyst by the chemical reduction of the AgNO₃ complex encapsulated fullerene microcrystal, which showed an enhanced catalytic reduction of 4-nitrophenol because of the strong absorption and propagation of H₂ along the fullerene surface. With the aid of visible-light radiation, photodegradation of orange G dye is achieved through the formation of an electron donor-acceptor dyad between plasmon Ag nanostructures and fullerene molecules, which effectively offsets the "electron-hole" recombination. Neither Ag nanoparticle nor fullerene crystal used in isolation could perform this chemical conversion, implying that the metal-fullerene hybrid structure is imperative for performing the catalytic reaction. The obtained Ag-embedded fullerene crystal is characterized by scanning electron microscopy (SEM), associated energy-dispersive X-ray spectroscopy (EDX) imaging, and X-ray photoelectron spectroscopy (XPS) and demonstrates that the present hybrid materials would add a supplemental member to a family of photocatalysts toward the organic synthesis and wastewater remediation.

Multifunctional molecular charge-transfer thin films

We report the controlled interfacial interaction in crystallized organic charge transfer thin films, consisting of bis(ethylenedithio)tetrathiafulvalene and C60. The induced broad-band absorption from the UV to near-infrared region leads to a wavelength dependent ambipolar (negative/positive) photoresponse, while multi-stimuli responsive behavior is achieved through charge-transfer interactions. In addition, by coupling with the tetrathiafulvalene-(7,7,8,8-tetracyanoquinodimethane) charge transfer complex, a significantly increased conductivity is achieved. The controlled interfacial charge transfer interaction provides an efficient approach to obtain multifunctional molecular crystallized thin films with a superior external stimuli response.

Ubiquitous energy conversion of two-dimensional molecular crystals

Two-dimensional (2D) atomic crystals have triggered significant excitement due to their rich physics as well as potential industrial applications. The possibility of a molecular counterpart with scalable processability and superior performance is intriguing from both fundamental and applied perspectives. Here, we present the freestanding 2D molecular charge-transfer bis(ethylenedithio)tetrathiafulvalene-C₆₀ crystals prepared by a modified Langmuir-Blodgett method, with precisely controlled few-layer thickness and centimeter-scale lateral dimension. The interconversion of intrinsic excited process, the long-range ordering and anisotropic stacking arrangement of the molecular layered crystals generate external stimuli responsive behaviors and anisotropic spin-charge conversion with magnetic energy conversion ability, as well as a superior UV photosensitivity. Moreover, the 2D freestanding crystals demonstrate superior magneto-electrical properties. These results suggest that a new class of 2D atomically thin molecular crystals with novel electronic, optical and magnetic properties have great potential for spintronic, energy and sensor applications.

Self-Assembled Metal Molecular Networks by Nanoconfinement

Quasi-two-dimensional (2D) metal molecular networks (MMNs) often exhibit a nanoconfinement effect and high degree of anisotropy, which are highly diverse in their mechanical, electronic, and magnetic functionalities. Here we report an interfacial self-assembly of mechanically robust 2D MMNs, in which 3d transition metals are interconnected via molecular thiol bridges. The Langmuir-Schäfer assembled freestanding 2D nanosheets exhibit highly desired anisotropic charge transport and spin susceptibility, in which light and magnetic field induced charge transfer regulates the electronic interactions. Meanwhile, the mechanistic studies involving electronic structure reveal the molecular metal packing structure-controlled nanoconfinement and charge transfer. This study opens the door to 2D ultrathin metal coordination nanostructures for emerging functional materials and devices.

Anisotropic Magnetoelectric Coupling and Cotton-Mouton Effects in the Organic Magnetic Charge-Transfer Complex Pyrene-F4TCNQ

Magnetoelectric coupling is of high current interest because of its potential applications in multiferroic memory devices. Although magnetoelectric coupling has been widely investigated in inorganic materials, such observations in organic materials are extremely rare. Here, we report our discovery that organic charge-transfer (CT) complex pyrene-2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (pyrene-F₄TCNQ) can display anisotropic magnetoelectric coupling. Investigation of the crystal structure of pyrene-F₄TCNQ complex demonstrates that the magnetoelectric coupling coefficient along the π-π interaction direction is much larger than the value along other directions. Furthermore, magnetoelectric coupling and magnetization can be tuned by changing the fluorine content in complexes. Besides, the Cotton-Mouton effect in pyrene-F₄TCNQ is observed, enabling the control of optomagnetic devices. These results can pave the way for a new method for the future development of organic CT complexes and their applications in perpendicular memory devices and energy-transfer-related multiferroics.

Tunable two-dimensional interfacial coupling in molecular heterostructures

Two-dimensional van der Waals heterostructures are of considerable interest for the next generation nanoelectronics because of their unique interlayer coupling and optoelectronic properties. Here, we report a modified Langmuir-Blodgett method to organize two-dimensional molecular charge transfer crystals into arbitrarily and vertically stacked heterostructures, consisting of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)/C₆₀ and poly(3-dodecylthiophene-2,5-diyl) (P3DDT)/C₆₀ nanosheets. A strong and anisotropic interfacial coupling between the charge transfer pairs is demonstrated. The van der Waals heterostructures exhibit pressure dependent sensitivity with a high piezoresistance coefficient of -4.4 × 10^-6 Pa^-1, and conductance and capacitance tunable by external stimuli (ferroelectric field and magnetic field). Density functional theory calculations confirm charge transfer between the n-orbitals of the S atoms in BEDT-TTF of the BEDT-TTF/C₆₀ layer and the π* orbitals of C atoms in C₆₀ of the P3DDT/C₆₀ layer contribute to the inter-complex CT. The two-dimensional molecular van der Waals heterostructures with tunable optical-electronic-magnetic coupling properties are promising for flexible electronic applications.Two-dimensional van der Waals heterostructures are of interest due to their unique interlayer coupling and optoelectronic properties. Here authors develop a Langmuir-Blodgett method to organize charge transfer molecular heterostructures with externally tunable conductance and capacitance and broadband photoresponse.