Refreshing the Legacy of Rudolf Nietzki: Benzene-1,2,4,5-tetramine and Related Compounds

Like hydroquinones and quinones, aromatic compounds with multiple NH2 groups and the corresponding quinonediimines have the potential to serve as components of useful redox-active organic materials. Benzene-1,2,4,5-tetramine (BTA) and its oxidized form BTA-H2 offer a promising redox pair of this type, and the compounds have proven to be useful in many areas of chemistry. However, key aspects of their behavior have remained poorly studied, such as the nature of their protonated forms, their preferred molecular structures, their reactivity, and their organization in condensed phases. In the present work, we have used a combination of improved methods of synthesis, computation, spectroscopic studies, and structural analyses to develop a deeper understanding of BTA, BTA-H2, their salts, and related compounds. The new knowledge is expected to accelerate exploitation of the compounds in areas of materials science where desirable properties can only be attained by properly controlling the organization of molecular components.

Electrical monitoring of organic crystal phase transition using MoS2 field effect transistor

Hybrid van der Waals heterostructures made of 2D materials and organic molecules exploit the high sensitivity of 2D materials to all interfacial modifications and the inherent versatility of the organic compounds. In this study, we are interested in the quinoidal zwitterion/MoS₂ hybrid system in which organic crystals are grown by epitaxy on the MoS₂ surface and reorganize in another polymorph after thermal annealing. By means of field-effect transistor measurements recorded in situ all along the process, atomic force microscopy and density functional theory calculations we demonstrate that the charge transfer between quinoidal zwitterions and MoS₂ strongly depends on the conformation of the molecular film. Remarkably, both the field effect mobility and the current modulation depth of the transistors remain unchanged which opens up promising prospects for efficient devices based on this hybrid system. We also show that MoS₂ transistors enable fast and accurate detection of structural modifications that occur during phases transitions of the organic layer. This work highlights that MoS₂ transistors are remarkable tools for on-chip detection of molecular events occurring at the nanoscale, which paves the way for the investigation of other dynamical systems.

Dimensionality Modulates Electrical Conductivity in Compositionally Constant One-, Two-, and Three-Dimensional Frameworks

We reveal here the construction of Ni-based metal-organic frameworks (MOFs) and conjugated coordination polymers (CCPs) with different structural dimensionalities, including closely π-stacked 1D chains (Ni-1D), aggregated 2D layers (Ni-2D), and a 3D framework (Ni-3D), based on 2,3,5,6-tetraamino-1,4-hydroquinone (TAHQ) and its various oxidized forms. These materials have the same metal-ligand composition but exhibit distinct electronic properties caused by different dimensionalities and supramolecular interactions between SBUs, ligands, and structural motifs. The electrical conductivity of these materials spans nearly 8 orders of magnitude, approaching 0.3 S/cm.

Significance Of Nuclear Quantum Effects In Hydrogen Bonded Molecular Chains

In hydrogen-bonded systems, nuclear quantum effects such as zero-point motion and tunneling can significantly affect their material properties through underlying physical and chemical processes. Presently, direct observation of the influence of nuclear quantum effects on the strength of hydrogen bonds with resulting structural and electronic implications remains elusive, leaving opportunities for deeper understanding to harness their fascinating properties. We studied hydrogen-bonded one-dimensional quinonediimine molecular networks which may adopt two isomeric electronic configurations via proton transfer. Herein, we demonstrate that concerted proton transfer promotes a delocalization of π-electrons along the molecular chain, which enhances the cohesive energy between molecular units, increasing the mechanical stability of the chain and giving rise to distinctive electronic in-gap states localized at the ends. These findings demonstrate the identification of a class of isomeric hydrogen-bonded molecular systems where nuclear quantum effects play a dominant role in establishing their chemical and physical properties. This identification is a step toward the control of mechanical and electronic properties of low-dimensional molecular materials via concerted proton tunneling.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting

The recent advances in the field of two-photon absorbing chromophores in the short-wavelength infrared spectral range (SWIR 1100–2500 nm) are summarized, highlighting the development of optical power limiting devices in this spectral range.

Electrical molecular switch addressed by chemical stimuli

We demonstrate that the conductance switching of benzo-bis(imidazole) molecules upon protonation depends on the lateral functional groups. The protonated H-substituted molecule shows a higher conductance than the neutral one (Gpro > Gneu), while the opposite (Gneu > Gpro) is observed for a molecule laterally functionalized by amino-phenyl groups. These results are demonstrated at various scale lengths: self-assembled monolayers, tiny nanodot-molecule junctions and single molecules. From ab initio theoretical calculations, we conclude that for the H-substituted molecule, the result Gpro > Gneu is correctly explained by a reduction of the LUMO-HOMO gap, while for the amino-phenyl functionnalized molecule, the result Gneu > Gpro is consistent with a shift of the HOMO, which reduces the density of states at the Fermi energy.

Di- vs. tetra-substituted quinonediimines: a drastic effect on coordination chemistry

N,N′-Di-substituted benzoquinonediimine ligands behave differently in coordination chemistry compared to the well-known N,N′,N′′,N′′′-tetra-substituted analogues.

A diquinone–imidazole ensemble for selective colorimetric sensing of cyanide in aqueous medium via anion induced NIR absorption

The receptor selectively and sensitively senses cyanide ions in aqueous solution with a striking colour changeviaanion induced NIR absorption (913 nm).