Transition metal dichalcogenides (TMDCs) are layered compounds where layers are held together by weak van der Waals (vdW) interactions and can be cleaved with ease, enabling the exfoliation of a single layer by means of physically thinning down the crystal. [1,2] This transition from 3D to 2D [2,3] is accompanied by a whole set of outstanding new physics of 2D TMDCs. [4-7] This started the quest for high-quality and large-scale monolayers, which fostered the development of different techniques ranging from bottom-up approaches like chemical vapor deposition (CVD) and molecular-beam epitaxy (MBE) [8] to top-down routes via mechanical and liquid exfoliation. [2,8,9] To date, all routes suffer specific drawbacks. Both CVD and MBE can supply large-area monolayers yet crave optimization for each new TMDC composition and bear challenges in terms of subsequent clean transfer off the growth substrate. Liquid-based exfoliations introduce contaminants, thereby limiting studies of intrinsic material properties. Historically, tape-based mechanical exfoliation has largely carried the advance on 2D material research and the study of their intrinsic properties by supplying high-quality materials in an accessible manner. However, it is easily diagnosed with low yield, limiting its use beyond lab-scale experiments. To overcome these limitations scalable exfoliations beyond scotch tape have been investigated. [10] On this note, gold has been investigated as an exfoliation substrate and provides the needed adhesive forces via strong vdW [11] or "covalent-like quasibonding" (CLQB) [12] interactions with layered materials. Several TMDCs have already been exfoliated using gold (Table S1,

Metal-free 2D covalent organic materials transport charges along and in-between π-conjugated layers. Here, we look at the prospects of graphitic carbon nitrides and covalent organic frameworks as 2D semiconductors “beyond graphene and silicon”.

Poly(triazine imide) (PTI) is a highly crystalline semiconductor, and though no techniques exist that enable synthesis of macroscopic monolayers of PTI, it is possible to study it in thin layer device applications that are compatible with its polycrystalline, nanoscale morphology. We find that the by‐product of conventional PTI synthesis is a C−C carbon‐rich phase that is detrimental for charge transport and photoluminescence. An optimized synthetic protocol yields a PTI material with an increased quantum yield, enabled photocurrent and electroluminescence. We report that protonation of the PTI structure happens preferentially at the pyridinic N atoms of the triazine rings, is accompanied by exfoliation of PTI layers, and contributes to increases in quantum yield and exciton lifetimes. This study describes structure–property relationships in PTI that link the nature of defects, their formation, and how to avoid them with the optical and electronic performance of PTI. On the basis of our findings, we create an OLED prototype with PTI as the active, metal‐free material.

Poly(triazine imide)…i of the family of graphitic carbon nitrides and its graphitic morphology allows exfoliation the material into solution-processable layers,while at the same time reducing migration and drift of chemically bonded dopants.Ateam of researchers from Humboldt-Universitätz uB erlin, Carl von Ossietzky UniversitätOldenburg,and Helmholtz-Zentrum Berlin (HZB) constructed the first thin layer, organic light emitting device (OLED) with asolution-processed graphitic organic material as am etal-free emission layer. Ford etails see the Research Article by Michael J. Bojdys et al. (e202111749).

Despite their inherent instability, 4n π systems have recently received significant attention due to their unique optical and electronic properties. In dibenzopentalene (DBP), benzanellation stabilizes the highly antiaromatic pentalene core, without compromising its amphoteric redox behavior or small HOMO− LUMO energy gap. However, incorporating such molecules in organic devices as discrete small molecules or amorphous polymers can limit the performance (e.g., due to solubility in the battery electrolyte solution or low internal surface area). Covalent organic frameworks (COFs), on the contrary, are highly ordered, porous, and crystalline materials that can provide a platform to align molecules with specific properties in a well-defined, ordered environment. We synthesized the first antiaromatic framework materials and obtained a series of three highly crystalline and porous COFs based on DBP. Potential applications of such antiaromatic bulk materials were explored: COF films show a conductivity of 4 × 10 −8 S cm −1 upon doping and exhibit photoconductivity upon irradiation with visible light. Application as positive electrode materials in Li-organic batteries demonstrates a significant enhancement of performance when the antiaromaticity of the DBP unit in the COF is exploited in its redox activity with a discharge capacity of 26 mA h g −1 at a potential of 3.9 V vs. Li/Li + . This work showcases antiaromaticity as a new design principle for functional framework materials.