Tuning magnetoresistance in molybdenum disulphide and graphene using a molecular spin transition

Cyano disubstituted tetrabenzoindeno[2,1-a]fluorene: open-shell or closed-shell?

Organic diradicaloids have lately emerged as potential spintronic materials. We report the unprecedented synthesis of a near-IR absorbing indeno[2,1-a]fluorene derivative that displays remarkably low LUMO (-4.15 eV) and a small HOMO-LUMO gap (0.85 eV). NMR/EPR studies indicated its open-shell diradical property, which was supported by DFT calculations while suggesting a 30% diradical character and a small singlet (S)-triplet (T) gap (-2.52 kcal mol-1). A large bond length alternation of the as-indacene core for its single-crystals indicated a quinoidal contribution with greater antiaromaticity, which is in line with the small diradical character despite showing a small S-T gap.

Comprehensive Insights into the Family of Atomically Thin 2D-Materials for Diverse Photocatalytic Applications

2D materials with their fascinating physiochemical, structural, and electronic properties have attracted researchers and have been used for a variety of applications such as electrocatalysis, photocatalysis, energy storage, magnetoresistance, and sensing. In recent times, 2D materials have gained great momentum in the spectrum of photocatalytic applications such as pollutant degradation, water splitting, CO2 reduction, NH3 production, microbial disinfection, and heavy metal reduction, thanks to their superior properties including visible light responsive band gap, improved charge separation and electron mobility, suppressed charge recombination and high surface reactive sites, and thus enhance the photocatalytic properties rationally as compared to 3D and other low-dimensional materials. In this context, this review spot-lights the family of various 2D materials, their properties and their 2D structure-induced photocatalytic mechanisms while giving an overview on their synthesis methods along with a detailed discussion on their diverse photocatalytic applications. Furthermore, the challenges and the future opportunities are also presented related to the future developments and advancements of 2D materials for the large-scale real-time photocatalytic applications.

Tunable electronic and magnetic properties of Cr2Ge2Te6monolayer by organic molecular adsorption

Recently, two-dimensional materials are widely concerned because of their novel physical properties. Cr₂Ge₂Te₆(CGT) has been studied extensively due to its intrinsic ferromagnetism and ferromagnetic order. In this investigation, the electronic and magnetic performances of organic molecules (TCNE, TCNQ and TTF) adsorbed on CGT monolayer were studied based on the first-principles calculations systematically. The results demonstrate that the CGT presents pronounced tunable electronic and magnetic properties by the adsorption of these macromolecules. Furthermore, the Curie temperature of CGT monolayer can be enhanced significantly by the TTF adsorption. This work can provide a magnetic regulation method for CGT and explore the promising applications of the CGT for spin devices.

Essential Role of Triplet Diradical Character for Large Magnetoresistance in Quinoidal Organic Semiconductor with High Electron Mobility

A diradicaloid molecule with high semiconducting performance is synthesized based on the quinoidal benzo[1,2-b:4,5-b']dithiophene structure. The diradical character is investigated by quantum chemical calculations and variable temperature electron spin resonance. The diode devices based on this molecule show a large change in electric current in magnetic fields below 100 mT with a strong dependence on the measurement temperatures; as the population of the triplet diradicals increases at high temperatures, the magnetoconductance (MC) values increase. As a result, a MC of -19.4% is achieved at 120 °C, which is the largest negative MC observed for organic molecules to date. In contrast, a smaller diradicaloid molecule based on quinoidal thieno[3,2-b]thiophene without thermally accessible triplet state shows no MC, indicating the essential role of the triplet diradicals. The strong correlation between the MC and the triplet diradical concentrations suggests that the charge conduction in the diradicaloid is suppressed through a spin-blocking mechanism, which can be controlled through the magnetic modulation of the hyperfine fields. The compound forms high-crystallinity thin films and has high monopolar electron transport in organic field-effect transistors, with an average mobility of 1.01 cm² V^-1 s^-1 for edge-cast films.

Chaotropic Effect Stabilized Radical-Containing Supramolecular Organic Frameworks for Photothermal Therapy

Radical-containing frameworks (RCFs) have emerged as promising functional materials in various fields due to the combination of the highly ordered frame structure and the fascinating property of organic radicals. Here, the first example of radical-containing supramolecular organic frameworks (SOFs) fabricated by the chaotropic effect between closo-dodecaborate cluster (B₁₂ H₁₂^2- ) and 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT³⁺ ) is presented. The SOFs can be easily synthesized by stirring the B₁₂ H₁₂^2- and the TPT³⁺ in aqueous solution through self-assembly. Upon 435 nm light irradiation, the SOFs exhibits photochromic behavior from slight yellow (SOF-1) to dark purple (SOF-2). Electron paramagnetic resonance spectroscopy also reveals that stable radicals are generated in situ after light irradiation. Powder X-ray diffraction demonstrates the SOFs maintain their structural stabilities upon light irradiation. More interestingly, the radical-containing SOFs exhibit efficient photothermal effect under 660 nm light irradiation, which can be applied as photothermal agent for antibacterial application both in vitro and in vivo. This work highlights the construction of RCFs through supramolecular self-assembly, which may arouse applications in energy, catalysis, photoluminescence, and biomedical fields.

Molecular Approach to Engineer Two-Dimensional Devices for CMOS and beyond-CMOS Applications

Two-dimensional materials (2DMs) have attracted tremendous research interest over the last two decades. Their unique optical, electronic, thermal, and mechanical properties make 2DMs key building blocks for the fabrication of novel complementary metal-oxide-semiconductor (CMOS) and beyond-CMOS devices. Major advances in device functionality and performance have been made by the covalent or noncovalent functionalization of 2DMs with molecules: while the molecular coating of metal electrodes and dielectrics allows for more efficient charge injection and transport through the 2DMs, the combination of dynamic molecular systems, capable to respond to external stimuli, with 2DMs makes it possible to generate hybrid systems possessing new properties by realizing stimuli-responsive functional devices and thereby enabling functional diversification in More-than-Moore technologies. In this review, we first introduce emerging 2DMs, various classes of (macro)molecules, and molecular switches and discuss their relevant properties. We then turn to 2DM/molecule hybrid systems and the various physical and chemical strategies used to synthesize them. Next, we discuss the use of molecules and assemblies thereof to boost the performance of 2D transistors for CMOS applications and to impart diverse functionalities in beyond-CMOS devices. Finally, we present the challenges, opportunities, and long-term perspectives in this technologically promising field.

Leveraging Molecular Properties to Tailor Mixed-Dimensional Heterostructures beyond Energy Level Alignment

The surface sensitivity and lack of dielectric screening in two-dimensional (2D) materials provide numerous intriguing opportunities to tailor their properties using adsorbed π-electron organic molecules. These organic-2D mixed-dimensional heterojunctions are often considered solely in terms of their energy level alignment, i.e., the relative energies of the frontier molecular orbitals versus the 2D material conduction and valence band edges. While this simple model is frequently adequate to describe doping and photoinduced charge transfer, the tools of molecular chemistry enable additional manipulation of properties in organic-2D heterojunctions that are not accessible in other solid-state systems. Fully exploiting these possibilities requires consideration of the details of the organic adlayer beyond its energy level alignment, including hybridization and electrostatics, molecular orientation and thin-film morphology, nonfrontier orbitals and defects, excitonic states, spin, and chirality. This Perspective explores how these relatively overlooked molecular properties offer unique opportunities for tuning optical and electronic characteristics, thereby guiding the rational design of organic-2D mixed-dimensional heterojunctions with emergent properties.

Open-Shell Nonbenzenoid Nanographenes Containing Two Pairs of Pentagonal and Heptagonal Rings

Nonbenzenoid carbocyclic rings are postulated to serve as important structural elements toward tuning the chemical and electronic properties of extended polycyclic aromatic hydrocarbons (PAHs, or namely nanographenes), necessitating a rational and atomically precise synthetic approach toward their fabrication. Here, using a combined bottom-up in-solution and on-surface synthetic approach, we report the synthesis of nonbenzenoid open-shell nanographenes containing two pairs of embedded pentagonal and heptagonal rings. Extensive characterization of the resultant nanographene in solution shows a low optical gap, and an open-shell singlet ground state with a low singlet-triplet gap. Employing ultra-high-resolution scanning tunneling microscopy and spectroscopy, we conduct atomic-scale structural and electronic studies on a cyclopenta-fused derivative on a Au(111) surface. The resultant five to seven rings embedded nanographene displays an extremely narrow energy gap of 0.27 eV and exhibits a pronounced open-shell biradical character close to 1 (y₀ = 0.92). Our experimental results are supported by mean-field and multiconfigurational quantum chemical calculations. Access to large nanographenes with a combination of nonbenzenoid topologies and open-shell character should have wide implications in harnessing new functionalities toward the realization of future organic electronic and spintronic devices.

Molecular chemistry approaches for tuning the properties of two-dimensional transition metal dichalcogenides

Two-dimensional (2D) semiconductors, such as ultrathin layers of transition metal dichalcogenides (TMDs), offer a unique combination of electronic, optical and mechanical properties, and hold potential to enable a host of new device applications spanning from flexible/wearable (opto)electronics to energy-harvesting and sensing technologies. A critical requirement for developing practical and reliable electronic devices based on semiconducting TMDs consists in achieving a full control over their charge-carrier polarity and doping. Inconveniently, such a challenging task cannot be accomplished by means of well-established doping techniques (e.g. ion implantation and diffusion), which unavoidably damage the 2D crystals resulting in degraded device performances. Nowadays, a number of alternatives are being investigated, including various (supra)molecular chemistry approaches relying on the combination of 2D semiconductors with electroactive donor/acceptor molecules. As yet, a large variety of molecular systems have been utilized for functionalizing 2D TMDs via both covalent and non-covalent interactions. Such research endeavours enabled not only the tuning of the charge-carrier doping but also the engineering of the optical, electronic, magnetic, thermal and sensing properties of semiconducting TMDs for specific device applications. Here, we will review the most enlightening recent advancements in experimental (supra)molecular chemistry methods for tailoring the properties of atomically-thin TMDs - in the form of substrate-supported or solution-dispersed nanosheets - and we will discuss the opportunities and the challenges towards the realization of novel hybrid materials and devices based on 2D semiconductors and molecular systems.

From open-shell singlet diradicaloids to polyradicaloids

In this Feature Article, we highlight our recent efforts toward stable open-shell singlet diradicaloids and polyradicaloids. A brief review on the historical works in the area is introduced first, followed by discussion on the fundamental electronic and physical properties of open-shell singlet diradicaloids. Then, the structure-diradical character relationships based on our recently developed diradicaloids are presented. Next, the challenges and solutions toward stable polyradicaloids and 3D π-conjugated diradicaloids are discussed. Finally, their preliminary material applications are introduced and a perspective view of the area is given.