Direct observation of electron transfer in solids through X-ray crystallography

Abstract Nanoscale electron transfer (ET) in solids is fundamental to the design of multifunctional nanomaterials, yet its process is not fully understood. Herein, through X-ray crystallography, we directly observe solid-state ET via a crystal-to-crystal process. We first demonstrate the creation of a robust and flexible electron acceptor/acceptor (A/A) double-wall nanotube crystal ([(Zn2+)4(LA)4(LA=O)4] n ) with a large window (0.90 nm × 0.92 nm) through the one-dimensional porous crystallization of heteroleptic Zn4 metallocycles ((Zn2+)4(LA)4(LA=O)4) with two different acceptor ligands (2,7-bis((1-ethyl-1H-imidazol-2-yl)ethynyl)acridine (LA) and 2,7-bis((1-ethyl-1H-imidazol-2-yl)ethynyl)acridin-9(10H)-one (LA=O)) in a slow-oxidation-associated crystallization procedure. We then achieve the bottom-up construction of the electron donor incorporated-A/A nanotube crystal ([(D)2⊂(Zn2+)4(LA)4(LA=O)4] n ) through the subsequent absorption of electron donor guests (D = tetrathiafulvalene (TTF) and ferrocene (Fc)). Finally, we remove electrons from the electron donor guests inside the nanotube crystal through facile ET in the solid state to accumulate holes inside the nanotube crystal ([(D•+)2⊂(Zn2+)4(LA)4(LA=O)4] n ), where the solid-state ET process (D – e– → D•+) is thus observed directly by X-ray crystallography

Studies on Pyrene and Perylene Derivatives upon Oxidation and Application to a Higher Analogue

The structure and electronic features of neutral and positively charged pyrene and perylene derivatives were explored. The radical cation of 1,3,6,8-tetraarylpyrene 1 was examined by ESR, UV-vis-NIR spectroscopy and theoretical calculations. The addition of 2 equiv of oxidant to 1 resulted in the formation of dication 12+. The single-crystal X-ray structure of 12+ proved that the aromatic part relocates from biphenyl unit to naphthyl unit upon 2e- oxidation of 1. We have also investigated the oxidation processes of 3,9-diarylperylene 2 and 3,10-diarylperylene 3. The radical cations of 2・+ and 3・+ showed ESR signals and the spin densities were proven to delocalize at 3,4,9,10-positions. In the case of doubly charged 3,9-diarylperylene, we could find the anthracene structure in the core, while the phenanthrene skeleton appeared in two-electron oxidized 3,10-diarylperylene. Finally we validated this phenomenon to apply for the higher analogue terrylene, discovering its large aromaticity relocation upon the 2e- oxidation

Self-Discriminating Termination of Chiral Supramolecular Polymerization: Tuning the Length of Nanofibers

Directing the supramolecular polymerization towards a preferred type of organization is extremely important in the design of functional soft materials. Proposed herein is a simple methodology to tune the length and optical chirality of supramolecular polymers formed from a chiral bichromophoric binaphthalene by the control of enantiomeric excess (ee). The enantiopure compound gave thin fibers longer than a few microns, while the racemic mixture favored the formation of nanoparticles. The thermodynamic study unveils that the heterochiral assembly gets preference over the homochiral assembly. The stronger heterochiral binding over homochiral one terminated the elongation of fibrous assembly, thus leading to a control over the length of fibers in the nonracemic mixtures. The supramolecular polymerization driven by π–π interactions highlights the effect of the geometry of a twisted π-core on this self-sorting assembly

OFF–ON–OFF Dual Emission at Visible and UV Wavelengths from Carbazole Functionalized β‑Diketonate Europium(III) Complex

This work demonstrates dual emission “OFF–ON–OFF” switching at visible and UV wavelengths of a carbazole functionalized β-diketone (LH) by a simple change of a europium­(III) ion (Eu³⁺) concentration in the submicromolar concentration range. In the presence of 0.25 equiv of Eu³⁺ (5 μM), LH forms a luminescent 4:1 complex ([Eu³⁺(L^–)₄]⁻) exhibiting dual emission at 357 and 613 nm resulting from the local excitation of the carbazole ring and ligand-sensitized luminescence from the Eu³⁺-β-diketonate unit, respectively. The 4:1 complex begins to convert into a 2:1 complex ([Eu³⁺(L^–)₂]⁺) via a 3:1 complex [Eu³⁺(L^–)₃] above a molar ratio ([Eu³⁺]/[LH]) of 0.25, which provides the opportunity for binding of solvent methanol molecules to the vacant site of the Eu³⁺ ion in the complex ([Eu³⁺(L^–)₂(MeOH)_<i>n</i>]⁺). The OH oscillators of coordinated methanol molecules facilitate the nonradiative pathway of the Eu³⁺ emission; hence the emission at 613 nm almost disappears above the 0.50 equivalent of Eu³⁺ (11 μM), while the UV emission at 357 nm remains mostly constant over the whole concentration range

Ligand-to-Ligand Interactions That Direct Formation of <i>D</i>₂‑Symmetrical Alternating Circular Helicate

This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis­(4-phenyl-2-oxazolinyl)­pyridine [(<i>R</i>)- or (<i>S</i>)-Ph-Pybox] are successfully directed to the fabrication of a <i>D</i>₂-symmetrical alternating circular helicate with the general formula [(<i>R</i>)- or (<i>S</i>)-Ph-Pybox]₄(Ln^III)₄(BTP)₆. The lanthanide­(III) Ln^III assemblies (Ln^III₄-<i>RRRR</i> and Ln^III₄-<i>SSSS</i>) have a nanometer-size squarelike grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate Ln^III₂L₂ units, where both show (<i>M</i>)-helicity for Ln^III₄-<i>RRRR</i> and (<i>P</i>)-helicity for Ln^III₄-<i>SSSS</i>, where π–π stacking interaction is present between the side arm of (<i>R</i>)-Ph-Pybox (Ph₁) and the adjacent BTP ligand around the Eu^III metal center (<i>d</i>_ππ = 3.636 Å: the diketonate plane···Ph₁ distance). The newly obtained circular lanthanide­(III) helicate exists as single and homochiral diastereomers in solution (Ln^III₄-<i>RRRR</i> and Ln^III₄-<i>SSSS</i>), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (i.e., Ln^III₄-<i>RRRR</i>/Ln^III₄-<i>SSSS</i>)

Ligand-to-Ligand Interactions That Direct Formation of <i>D</i>₂‑Symmetrical Alternating Circular Helicate

This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis­(4-phenyl-2-oxazolinyl)­pyridine [(<i>R</i>)- or (<i>S</i>)-Ph-Pybox] are successfully directed to the fabrication of a <i>D</i>₂-symmetrical alternating circular helicate with the general formula [(<i>R</i>)- or (<i>S</i>)-Ph-Pybox]₄(Ln^III)₄(BTP)₆. The lanthanide­(III) Ln^III assemblies (Ln^III₄-<i>RRRR</i> and Ln^III₄-<i>SSSS</i>) have a nanometer-size squarelike grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate Ln^III₂L₂ units, where both show (<i>M</i>)-helicity for Ln^III₄-<i>RRRR</i> and (<i>P</i>)-helicity for Ln^III₄-<i>SSSS</i>, where π–π stacking interaction is present between the side arm of (<i>R</i>)-Ph-Pybox (Ph₁) and the adjacent BTP ligand around the Eu^III metal center (<i>d</i>_ππ = 3.636 Å: the diketonate plane···Ph₁ distance). The newly obtained circular lanthanide­(III) helicate exists as single and homochiral diastereomers in solution (Ln^III₄-<i>RRRR</i> and Ln^III₄-<i>SSSS</i>), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (i.e., Ln^III₄-<i>RRRR</i>/Ln^III₄-<i>SSSS</i>)