Herein, we address the question whether anion–π and cation–π interactions can take place simultaneously on the same aromatic surface. Covalently positioned carboxylate–guanidinium pairs on the surface of 4-amino-1,8-naphthalimides are used as an example to explore push–pull chromophores as privileged platforms for such “ion pair–π� interactions. In antiparallel orientation with respect to the push–pull dipole, a bathochromic effect is observed. A red shift of 41 nm found in the least polar solvent is in good agreement with the 70 nm expected from theoretical calculations of ground and excited states. Decreasing shifts with solvent polarity, protonation, aggregation, and parallel carboxylate–guanidinium pairs imply that the intramolecular Stark effect from antiparallel ion pair–π interactions exceeds solvatochromic effects by far. Theoretical studies indicate that carboxylate–guanidinium pairs can also interact with the surfaces of π-acidic naphthalenediimides and π-basic pyrenes.

The hydration of Th(IV) in ThCl₄ and ThBr₄ water solutions at different salt concentrations was studied in order to understand the structure of Th(IV) in liquid water and the effect of Br^– and Cl^– anions on its hydration structure. Several theoretical methods were employed: density functional theory and classical molecular dynamics based on both semiempirical polarizable potentials and ab initio derived polarizable potentials. The results of the computations were combined with extended X-ray absorption fine structure (EXAFS) experimental data. The results of this study show that in pure water the Th–O distance of 2.45 Ã… corresponds to a first shell coordination number between 9 and 10. In the salt solutions, while Br^– does not affect directly the hydration of Th(IV) also at relatively high concentrations, Cl^–, on the other hand, is more structured around Th(IV), in agreement with recent high-energy X-ray scattering experiments. Counterions, even at relatively high concentrations (0.8 m), do not enter in the first solvation shell of Th(IV), but they induce an increase of water molecules in the first and second hydration shells of Th(IV).

This work illustrates a simple approach for optimizing the lanthanide luminescence in molecular dinuclear lanthanide complexes and identifies a particular multidentate europium complex as the best candidate for further incorporation into polymeric materials. The central phenyl ring in the bis-tridentate model ligands L3–L5, which are substituted with neutral (X = H, L3), electron-withdrawing (X = F, L4), or electron-donating (X = OCH₃, L5) groups, separates the 2,6-bis(benzimidazol-2-yl)pyridine binding units of linear oligomeric multi-tridentate ligand strands that are designed for the complexation of luminescent trivalent lanthanides, Ln(III). Reactions of L3–L5 with [Ln(hfac)₃(diglyme)] (hfac^– is the hexafluoroacetylacetonate anion) produce saturated single-stranded dumbbell-shaped complexes [Ln₂(Lk)(hfac)₆] (k = 3–5), in which the lanthanide ions of the two nine-coordinate neutral [N₃Ln(hfac)₃] units are separated by 12–14 Ã…. The thermodynamic affinities of [Ln(hfac)₃] for the tridentate binding sites in L3–L5 are average (6.6 ≤ log(β_2,1^Y,Lk) ≤ 8.4) but still result in 15–30% dissociation at millimolar concentrations in acetonitrile. In addition to the empirical solubility trend found in organic solvents (L4 > L3 >> L5), which suggests that the 1,4-difluorophenyl spacer in L4 is preferable, we have developed a novel tool for deciphering the photophysical sensitization processes operating in [Eu₂(Lk)(hfac)₆]. A simple interpretation of the complete set of rate constants characterizing the energy migration mechanisms provides straightforward objective criteria for the selection of [Eu₂(L4)(hfac)₆] as the most promising building block.

We present the results of a quantum chemical and classical molecular dynamics simulation study of some solutions containing chloride salts of La³⁺, Gd³⁺, and Er³⁺ at various concentrations (from 0.05 to 5 M), with the purpose of understanding their structure and dynamics and analyzing how the coordination varies along the lanthanide series. In the La−Cl case, nine water molecules surround the central La³⁺ cation in the first solvation shell, and chloride is present only in the second shell for all solutions but the most concentrated one (5 M). In the Gd³⁺ case, the coordination number is ~8.6 for the two lowest concentrations (0.05 and 0.1 M), and then it decreases rapidly. In the Er³⁺ case, the coordination number is 7.4 for the two lowest concentrations (0.05 and 0.1 M), and then it decreases. The counterion Cl^− is not present in the first solvation shell in the La³⁺ case for most of the solutions, but it becomes progressively closer to the central cation in the Gd³⁺ and Er³⁺ cases, even at low concentrations.