Influence of Tartrate Ligand Coordination over Luminescence Properties of Chiral Lanthanide-Based Metal-Organic Frameworks

The present work reports on a detailed discussion about the synthesis, characterization, and luminescence properties of three pairs of enantiopure 3D metal-organic frameworks (MOFs) with general formula {[Ln₂(L/D-tart)₃(H₂O)₂]·3H₂O}_n (3D_Ln-L/D, where Ln = Sm(III), Eu(III) or Gd(III), and L/D-tart = L- or D-tartrate), and ten pairs of enantiopure 2D coordination polymers (CPs) with general formula [Ln(L/D-Htart)₂(OH)(H₂O)₂]_n (2D_Ln-L/D, where Ln = Y(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III) or Yb(III), and L/D-Htart = hydrogen L- or D-tartrate) based on single-crystal X-ray structures. Enantiopure nature of the samples has been further corroborated by Root Mean Square Deviation (RMSD) as well as by circular dichroism (CD) spectra. Solid-state emission spectra of Eu(III), Tb(III), and Dy(III)-based compounds confirm the occurrence of ligand-to-metal charge transfers in view of the characteristic emissions for these lanthanide ions, and emission decay curves were also recorded to estimate the emission lifetimes for the reported compounds. A complete theoretical study was accomplished to better understand the energy transfers occurring in the Eu-based counterparts, which allows for explaining the different performances of 3D-MOFs and 2D-layered compounds. As inferred from the colorimetric diagrams, emission characteristics of Eu-based 2D CPs depend on the temperature, so their luminescent thermometry has been determined on the basis of a ratiometric analysis between the ligand-centered and Eu-centered emission. Finally, a detailed study of the polarized luminescence intensity emitted by the samples is also accomplished to support the occurrence of chiro-optical activity.

Application of temperature-controlled chiral hybrid structures constructed from copper(ii)-monosubstituted Keggin polyoxoanions and copper(ii)-organoamine complexes in enantioselective sensing of tartaric acid

Temperature usually occupies a crucial position in the construction of chiral compounds. By controlling the temperature of the reaction system, chiral and non-chiral compounds can be designed and synthesized. Given the above, three new chiral and non-chiral compounds based on copper(ii) monosubstituted polyoxoanions and Cu(en) complexes (en = ethylenediamine), d/l-[Cu(H₂O)(en)₂]₂{[Cu(H₂O)₂(en)][SiCuW₁₁O₃₉]}·5H₂O (1, d-1 and l-1) and [Cu(H₂O)(en)₂]{[Cu(en)₂]₂[SiCuW₁₁O₃₉]}·2.5H₂O (2), were successfully synthesized under hydrothermal conditions. The main synthesis conditions of compound 1 (d-1 and l-1) and compound 2 are the same, however, the only difference is that the reaction temperatures are 80 °C and 140 °C, respectively. What's more, compounds 1 and 2 can form a 1D chiral chain by Cu–O and W/Cu–O–W/Cu bonds, respectively, and further obtain a 3D-supramolecular framework through hydrogen bonding interaction. Meanwhile, due to the asymmetry of chiral compound 1, optical second-harmonic generation (SHG) was used to investigate the second-order nonlinear optical effect and it was found that the observed SHG efficiency of compound 1 is 0.3 times that of urea. To further investigate the chiral properties, d-1 and l-1 were used in the electrochemical enantioselective sensing of d-/l-tartaric acid (d-/l-tart) molecules, respectively, which demonstrates that d-1 and l-1 have a good application prospect in sensing chiral substances.

A pair of temperature-controlled chiral compounds, d- and l-[Cu(en)₂(H₂O)]₂{[Cu(en)(H₂O)₂][SiCuW₁₁O₃₉]}·5H₂O (en = ethanediamine) are isolated by hydrothermal method, having a good application prospect in sensing d-/l-tartaric acid.

Preparation of chiral graphene oxides by covalent attachment of chiral cysteines for voltammetric recognition of tartrates

The authors describe the preparation of a chiral graphene oxides (GOs) by covalent attachment of D- or L-cysteine using a one-step hydrothermal method. The resulting chiral functionalized GOs shows circular dichroism with intensities similar to those produced by the cysteines. This indicates that the chirality of cysteines is well preserved in the chiral GOs. The material is reasonably stable at temperatures from 20 to 200 °C and at pH values from 0 to 14. A glassy carbon electrode (GCE) was modified with the chiral GOs and then tested for recognition capability for L- and D-tartrate (0.5 mM). The enantioselectivity of the chiral GOs appears to be the result of a synergistic effect where GO increases the conductivity and cysteine provides the chiral environment. The method is assumed to provide a useful general scheme for development of advanced carbonaceous materials with chiral recognition capabilities. Graphical abstract Chiral graphene oxides produced by covalently attaching chiral amino acids displays effective enantioselective recognition. Graphical abstract contains poor quality of text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have uploaded the modified version as Graphical abstract.

Nitrogen and sulfur co-doped chiral carbon quantum dots with independent photoluminescence and chirality

Chiral CQDs exhibit strong PL and outstanding enantioselective electrochemical recognition ability. Moreover, chiral CQDs possess independent PL and chiral properties.

One-step synthesis of chiral carbon quantum dots and their enantioselective recognition

Chiral carbon quantum dots (l-carbon quantum dots, l-CQDs; and d-carbon quantum dots, d-CQDs) were synthesized through the facile hydrothermal treatment of carbonated citric acid and l-cysteine (or d-cysteine).

Strong intermolecular exciton couplings in solid-state circular dichroism of aryl benzyl sulfoxides

A series of 13 enantiopure aryl benzyl sulfoxides () with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on "dimers" composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed.