Emissive covalent organic frameworks (COFs) have recently emerged as next-generation porous materials with attractive properties such as tunable topology, porosity, and inherent photoluminescence. Among the different types of COFs, substoichiometric frameworks (so-called Type III COFs) are especially attractive due to the possibility of not only generating unusual topology and complex pore architectures but also facilitating the introduction of well-defined functional groups at precise locations for desired functions. Herein, the first example of a highly emissive (PLQY 6.8%) substoichiometric 2D-COF (COF-SMU-1) featuring free uncondensed aldehyde groups is reported. In particular, COF-SMU-1 features a dual-pore architecture with an overall bex net topology, tunable emission in various organic solvents, and distinct colorimetric changes in the presence of water. To gain further insights into its photoluminescence properties, the charge transfer, excimer emission, and excited state exciton dynamics of COF-SMU-1 are investigated using femtosecond transient absorption spectroscopy in different organic solvents. Additionally, highly enhanced atmospheric water-harvesting properties of COF-SMU-1 are revealed using FT-IR and water sorption studies.The findings will not only lead to in-depth understanding of structure-property relationships in emissive COFs but also open new opportunities for designing COFs for potential applications in solid-state lighting and water harvesting.

We report the phase diagram for the binary creatine–citric acid mixture which features a stable and broad eutectic region.

β-Naphthol reds are a group of widely used pigments with prominent historical, commercial, and cultural significance. In industry, and especially within the art and heritage community, they are known as azo pigments. However, β-naphthols, very often, are not azo pigments. Because of enol/keto tautomerization of the 1-arylhydrazone-2-naphthol skeleton, these pigments oftentimes crystallize as hydrazones (keto). Therefore, proper characterization is necessary for understanding their intrinsic physicochemical properties and chemical reactivity in the solid state, as well as their stability and lightfastness. Crystallographic studies have indicated that β-naphthol reds tend to adopt the hydrazone form in the solid state. Here, we continue these structural investigations, and we focused on two prominent β-naphthol reds, pigment red 40 (PR40) and pigment red 4 (PR4). Using single-crystal X-ray diffraction, we provide decisive proof that both of these pigments are keto/hydrazones in the solid state. Therefore, the frequent yet erroneous designation as azo pigments should be avoided. To confirm the bulk structure, we performed powder diffraction experiments, followed by Rietveld refinement. We complemented the diffraction experiments with spectroscopic (IR, Raman, UV–vis) and thermal (TGA, DSC) analyses. Furthermore, we studied the lightfastness of both chromophores in solution and the solid state. While the solid-state pigments were stable over the course of the experiment, UV irradiation of solutions resulted in degradation, which was studied by chromatographic and mass-spectrometry techniques. We hope that this research will bring to light the necessity of proper solid-state characterization of β-naphthol reds, as well as pigments as a whole.

β-Naphthol reds are a group of widely used pigments with prominent historical, commercial, and cultural significance. In in-dustry, and especially within the art and heritage community, they are known as azo pigments. However, β-naphthols, very often, are not azo pigments. Due to enol/keto tautomerization of the 1-arylhydrazone-2-naphthol skeleton, these pigments oftentimes crystallize as hydrazones (keto). Therefore, proper characterization is necessary for understanding their intrinsic physicochemical properties and chemical reactivity in the solid state, as well as stability and lightfastness. Here, we focused on two representative β-naphthol reds, pigment red 40 (PR40) and pigment red 4 (PR4). Using single-crystal X-ray diffraction, we provide decisive proof that both of these pigments are keto/hydrazones in the solid state. Therefore, the frequent yet erroneous designation as azo pigments should be avoided. To confirm the bulk structure, we performed powder diffraction experiments, followed by Rietveld refinement. We complemented the diffraction experiments with spectroscopic (IR, Raman, UV-vis) and thermal (TGA, DSC) analyses. Furthermore, we studied the lightfastness of both chromophores in solution and solid state. While the solid state pigments were stable over the course of the experiment, UV irradiation of solutions resulted in degradation, which was studied by chromatographic and mass-spec techniques. We hope that this research will bring to light the necessity of proper solid-state characterization of β-naphthol reds, as well as pigments as a whole.

We report the phase diagram for the binary creatine–citric acid mixture which features a stable and broad eutectic region. Combinations containing 10–60 mol% creatine yield a deep eutectic solvent with a glass transition temperature at 270 K. Addition of up to 70 mol% water to the binary mixture affords retention of the eutectic nature and a handle to vary solvent viscosity and polarity.