π–π Interactions Between Aromatic Groups in Amphiphilic Molecules: Directing Hierarchical Growth of Porous Zeolites

The development of hierarchical macro- or mesoporous zeolites is essential in zeolite synthesis because the size of the micropores limits mass transport and their use as industrial catalysts for bulky molecules. Although major breakthroughs have been achieved, fabricating crystallographically ordered mesoporous zeolites using a templating strategy is still an unsolved challenge. This minireview highlights our recent efforts on the self-assembly of amphiphilic molecules to obtain ordered hierarchical MFI zeolites by introducing aromatic groups into the hydrophobic tail of the amphiphilic molecules. Owing to the geometric matching between the self-assembled aromatic tails and the MFI framework, a) single-crystalline mesostructured zeolite nanosheets (SCZNs), b) SCZNs with a 90° rotational intergrowth structure, c) a hierarchical MFI zeolite with a two-dimensional square P4mm mesostructure, and d) a single-crystalline mesoporous ZSM-5 with three-dimensional pores and sheetlike mesopores layered along the a-axis were successfully synthesized.     

Highly efficient organic photosensitizer with aggregation-induced emission for imaging-guided photodynamic ablation of cancer cells

We design an organic photosensitizer with a donor-π-acceptor configuration. The photosensitizer exhibits aggregation-induced emission characteristics and efficient singlet oxygen production in the aggregated state. It is then enveloped into the water-soluble micelle to afford a nanoprobe. The water-soluble nanoprobe keeps the photosensitizer in the aggregation state and is used for imaging-guided photodynamic ablation of cancer cells.     

Recent topics on catalytic transformations of aromatic molecules via η6-arene transition metal complexes

The π-complexation of an arene to a transition metal center delivers many useful reactivities to the arene moiety. Although synthetic methodologies that take advantage of such π-coordination have mostly been developed as stoichiometric processes, there have been considerable recent advances in the catalytic transformations of aromatic molecules through their activation in the form of transition metal η⁶-arene complexes. These advances include the π-coordination catalyzed transformations of aryl-heteroatom and side-chain CH and CC bonds and the palladium-catalyzed CH functionalization in pre-formed transition metal η⁶-arene complexes. This digest paper aims to provide a concise view of these recent advances in the area of transition metal η⁶-arene complexes.     

The strength of the σ-, π- and δ-bonds in Re2Cl 8 2−

The geometry of Re₂Cl₈²⁻ has been optimized for the eclipsed (D _4h ) equilibrium conformation and for the staggered (D _4d ) conformation at BP86/TZ2P. The nature of the Re–Re bond which has a formal bond order four has been studied with an energy decomposition analysis (EDA). The EDA investigation indicates that the contribution of the b ₂ (δ _xy ) orbitals to the Re–Re bond in the ground state is negligibly small. The vertical excitation of one and two electrons from the bonding δ orbital into the antibonding δ* orbitals yielding the singly and doubly excited states and gives a destabilization of 17.5 and 36.1 kcal/mol, respectively, which is nearly the same as the total excitation energies. The preference for the D _4h geometry with eclipsing Re–Cl bonds is explained in terms of hyperconjugation rather than δ bonding. This is supported by the calculation of the triply bonded Re₂Cl₈ which also has an eclipsed energy minimum structure. The calculations also suggest that the Re–Re triple bond in Re₂Cl₈ is stronger than the Re–Re quadruple bond in Re₂Cl₈²⁻. A negligible contribution of the δ orbital to the metal–metal bond strength is also calculated for Os₂Cl₈ which is isoelectronic with Re₂Cl₈²⁻. Contribution of the Mark S. Gordon 65th Birthday Festschrift Issue. Theoretical Studies of Inorganic Compounds. 38. Part 37 (2006) Bessac F, Frenking G, Inorg Chem 45:6956.     

芳环超分子体系中的π-π作用

π-π作用是芳环超分子体系中广泛存在的一种重要的弱相互作用. 本文对π-π作用的特征、形式、有效参数和表征方法等作了比较全面的综述, 同时小结了影响π-π作用的一些重要因素, 最后还概述了近年来π-π作用在超分子组装、不对称催化、有机半导体材料等领域的研究进展.     

Perfectly Encoding π-Conjugated Anions in the RE5(C3N3O3)(OH)12 (RE=Y,Yb, Lu) Family with Strong Second Harmonic Generation Response and Balanced Birefringence

Nonlinear optical (NLO) crystal, which simultaneously exhibits strong second-harmonic-generation (SHG) response and desired optical anisotropy, is a core optical material accessible to the modern optoelectronics. Accompanied by strong SHG effect in a NLO crystal, a contradictory problem of overlarge birefringence is ignored, leading to low frequency doubling efficiency and poor beam quality. Herein, a series of rare earth cyanurates RE₅(C₃N₃O₃)(OH)₁₂ (RE=Y, Yb, Lu) were successfully characterized by 3D electron diffraction technique. Based on a “three birds with one stone” strategy, they enable the simultaneous fulfillment of strong SHG responses (2.5–4.2× KH₂PO₄), short UV cutoff (ca. 220 nm) and applicable birefringence (ca. 0.15 at 800 nm) by the introduction of rare earth coordination control of π-conjugated (C₃N₃O₃)³⁻ anions. These findings provide high-performance short-wavelength NLO materials and highlight the exploration of cyanurates as a new research area.     

Anthracene-Fused Oligo-BODIPYs: A New Class of π-Extended NIR-Absorbing Materials

Large π-conjugated systems are key in the area of molecular materials. Herein, we prepare via Au^I-catalyzed cyclization a series of fully π-conjugated anthracene-fused oligo-BODIPYs. Their structural and optoelectronic properties were studied by several techniques, ranging from X-ray, UV/Vis, and cyclic voltammetry to transient absorption spectroscopy. As a complement, their electronic structures were explored by means of Density Functional Theory (DFT) calculations. Depending on the size and shape of the π-conjugated skeleton, unique features—such as face-to-face supramolecular organization, NIR absorption and fluorescence as well as strong electron accepting character—were noted. All in all, the aforementioned features render them valuable for technological applications.     

A Triply Negatively Charged Nanographene Bilayer with Spin Frustration

We report on the largest open-shell graphenic bilayer and also the first example of triply negatively charged radical π-dimer. Upon three-electron reduction, bilayer nanographene fragment molecule (C₉₆H₂₄Ar₆)₂ (Ar=2,6-dimethylphenyl) ( 1 ₂) was transformed to a triply negatively charged species 1 ₂^3.−, which has been characterized by single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic properties on a superconducting quantum interference device (SQUID). 1 ₂^3.− features a 96-center-3-electron (96c/3e) pancake bond with a doublet ground state, which can be thermally excited to a quartet state. It consists of 34 π-fused rings with 96 conjugated sp² carbon atoms. Spin frustration is observed with the frustration parameter f>31.8 at low temperatures in 1 ₂^3.−, which indicates graphene upon reduction doping may behave as a quantum spin liquid.     

A π-Conjugated Anion-Exchange Membrane with an Ordered Ion-Conducting Channel via the McMurray Coupling Reaction

The McMurry coupling is a facile, gentle and low-cost chemical reaction for synthesizing. Here, for the first time, we employed the McMurry coupling reaction to prepare π-conjugated anion exchange membranes (AEMs). The inter-chain π-π stacking between adjacent benzene rings induces directional self-assembly aggregation and enables highly ordered ion-conductive channels. The resulting structure was characterized through UV/VIS spectrum, X-ray diffraction (XRD) pattern, small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and density functional theory (DFT) calculations, leading to high OH⁻ conductivity of 135.5 mS cm⁻¹ at 80 °C. Furthermore, the double bonds in the π-conjugated system also trigger in situ self-crosslinking of the AEMs to enhance dimensional and alkaline stability. Benefiting from this advantage, the as-obtained Cr-QPPV-2.51 AEM exhibits superior alkaline stability (95 % conductivity retention after 3000 hrs in 1 M KOH at 80 °C) and high mechanical strength of 34.8 MPa. Moreover, the fuel cell using Cr-QPPV-2.51 shows a maximum peak power density of 1.27 W cm⁻² at 80 °C.     

Ruthenium-Catalyzed Activation of Nonpolar C−C Bonds via π-Coordination-Enabled Aromatization

Activation of C−C bonds allows editing of molecular skeletons, but methods for selective activation of nonpolar C−C bonds in the absence of a chelation effect or a driving force derived from opening of a strained ring are scarce. Herein, we report a method for ruthenium-catalyzed activation of nonpolar C−C bonds of pro-aromatic compounds by means of π-coordination-enabled aromatization. This method was effective for cleavage of C−C(alkyl) and C−C(aryl) bonds and for ring-opening of spirocyclic compounds, providing an array of benzene-ring-containing products. The isolation of a methyl ruthenium complex intermediate supports a mechanism involving ruthenium-mediated C−C bond cleavage.