Helical nanostructures self-assembled from optically active phthalocyanine derivatives bearing four optically active binaphthyl moieties: effect of metal-ligand coordination on the morphology, dimension, and helical pitch of self-assembled nanostructures

Metal-Enhanced Helical Chirality of Coil Macromolecules: Bioinspired by Metal Coordination-Induced Protein Folding

Although the supramolecular helical structures of biomacromolecules have been studied, the examples of supramolecular systems that are assembled using coils to form helical polymer chains are still limited. Inspired by enhanced helical chirality at the supramolecular level in metal coordination-induced protein folding, a series of alanine-based coil copolymers (poly-(l-co-d)-ala-NH₂) carrying (l)- and (d)-alanine pendants were synthesized as a fresh research model to study the cooperative processes between homochirality property and metal coordination. The complexes of poly-(l-co-d)-ala-NH₂ and metal ions underwent a coil-to-helix transition and exhibited remarkable nonlinear effects based on the enantiomeric excess of the monomer unit in the copolymers, affording enhanced helical chirality compared to poly-(l-co-d)-ala-NH₂. More importantly, the synergistic effect of amplification of asymmetry and metal coordination triggered the formation of a helical molecular orbital on the polymer backbone via the coordination with the d orbital of copper ions. Thus, the helical chirality enhancement degree of poly-(l-co-d)-ala-NH₂/Cu²⁺ complexes (31.4) is approximately 3 times higher than that of poly-(l-co-d)-ala-NH₂/Ag⁺ complexes (9.8). This study not only provides important mechanistic insights into the enhancement of helical chirality for self-assembly but also establishes a new strategy for studying the homochiral amplification of asymmetry in biological supramolecular systems.

Wide-Range and Highly Sensitive Chiral Sensing by Discrete 2D Chirality Transfer on Confined Surfaces of Au(I)-Thiolate Nanosheets

Circular dichroism (CD) chiral sensing is very promising to meet the ever-increasing demands for high-throughput chiral analysis in asymmetric synthesis. However, it is still very challenging to sensitively quantify the composition of enantiomers in a wide concentration range because the existing sensing systems show either linear CD response resultant from stoichiometric chiral transfer or nonlinear CD response resultant from amplified chiral transfer and thus have the drawbacks of low sensitivity and narrow quantification range, respectively. Herein, we propose a sensing system of two-dimensional (2D) Au(I)-thiolate nanosheets. The disordered interligand interactions on the confined surfaces of nanosheets enable the formation of discrete amplified chiral domains around the adsorbed chiral analytes, resulting in a linearly amplified chiral transfer behavior, which provides a solution for highly sensitive and wide-range quantification of enantiomer compositions. Taking (1R, 2R)-(-)- and (1S, 2S)-(+)-1,2-diamino cyclohexanes as example analytes, the concentration and full-range enantiomeric excess (ee) values have been quickly determined by adsorbing them on the surface of Au(I)-MPA (MPA: 3-mercaptopropionic acid) nanosheets in the concentration range of 1.0 × 10^-6 to 4.0 × 10^-5 M. By engineering the surface functional groups, Au(I)-thiolate nanosheets can be extended to sense other types of analytes, and several polyols with multiple chiral centers have been sensed by boronic acid functionalized nanosheets at the 10^-7 M level. The high performances, good extendibility, and one-pot high-yield aqueous synthesis ensure these Au(I)-thiolate nanosheets can be developed as a practical and powerful chiral sensing platform.

Helical-Ribbon and Tape Formation of Lipid Packaged [Ru(bpy)3]2+ Complexes in Organic Media

Anionic lipid amphiphiles with [RuII(bpy)3]2+ complex have been prepared. The metal complexes have been found to form ribbon and tape structures depending on chemical structures of lipid amphiphiles. Especially, the composites showed hypochromic effect and induced circular dichroism in organic media, and flexibly and weakly supramolecular control of morphological and optical properties have been demonstrated.

Cation-controlled catalysis with crown ether-containing transition metal complexes

This Feature Article reviews the structural motifs and catalytic applications of crown ether-containing catalysts and details the development of “pincer-crown ether” ligands for applications in controlled catalysis.

Chiral expression from molecular to macroscopic level via pH modulation in terbium coordination polymers

Chiral expression from the molecular to macroscopic level is common in biological systems, but is difficult to realise for coordination polymers (CPs). The assembly of homochiral CPs in both crystalline and helical forms can provide a bridge for understanding the relationship between the molecular and macroscopic scales of chirality. Herein, we report homochiral helices of [Tb(R- or S-pempH)₃]∙2H₂O (R - or S -1) (pempH₂ = (1-phenylethylamino)methylphosphonic acid) and their crystalline counterparts (R - or S -3), which are formed at different pH of the reaction mixtures under hydrothermal conditions. By combining the experiments and molecular simulations, we propose that the formation of helices of R -1 or S -1 occurs via a hierarchical self-assembly route, which involves twisted packing due to the geometric incompatibility of the different types of chains. The observed chiral transcription from molecules to morphologies is significant for understanding bio-related self-assembly processes on the nano- to macro-scale.

Optically Active Porphyrin and Phthalocyanine Systems

This review highlights and summarizes various optically active porphyrin and phthalocyanine molecules prepared using a wide range of structural modification methods to improve the design of novel structures and their applications. The induced chirality of some illustrative achiral bis-porphyrins with a chiral guest molecule is introduced because these systems are ideal for the identification and separation of chiral biologically active substrates. In addition, the relationship between CD signal and the absolute configuration of the molecule is analyzed through an analysis of the results of molecular modeling calculations. Possible future research directions are also discussed.

Design of UV-Vis-NIR panchromatic crown-phthalocyanines with controllable aggregation

Novel magnesium and zinc phthalocyaninates, bearing four lateral electron-rich 15-crown-5-oxanthrene fragments, were synthesized starting from benzo-15-crown-5. Being almost insoluble in common organic solvents, these complexes could be solubilised by interaction with potassium acetate due to the formation of well-defined cofacial supramolecular dimers. A characteristic feature of these dimers is the presence of additional bands in their UV-Vis spectra, which affords the expansion of light absorption region up to ∼750 nm. This new band corresponds to the charge transfer from the peripheral groups to the Pc core, as evidenced by TDDFT calculations. Potassium cations can be reversibly removed from these dimers by [2.2.2]cryptand, resulting in the formation of monodisperse nanoparticles exhibiting absorbances up to 900 nm. This approach can be further used for the fabrication of nanostructured optoelectronic materials based on the synthesized donor-acceptor panchromatic crown-phthalocyanines.

Supramolecular self-assembly and photovoltaic property of soluble fluorogallium phthalocyanine

Fluorogallium tetra-tert-butylphthalocyanine (ttbPcGaF) can self-organize into well-ordered cofacial structures to obtain one-dimensional (1D) supramolecular polymers in the solid state using a solution-coating technique. The ttbPcGaF-based BHJ OSC provided a profoundly improved power conversion efficiency (PCE) of 0.41%.

Self-assembled nanostructures of optically active phthalocyanine derivatives. Effect of central metal ion on the morphology, dimension, and handedness

Four optically active {(2,3,9,10,16,17,23,24-octa[(S)-2-methylbutoxy]} phthalocyanine derivatives with different central metal ions, namely (S)-H2Pc(β-OC5H11)8 (1), (S)-ZnPc(β-OC5H11)8 (2), (S)-CuPc(β-OC5H11)8 (3), and (S)-NiPc(β-OC5H11)8 (4) have been synthesized and their self-assembly behaviors systematically investigated by electronic absorption and circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) techniques, and X-ray photoelectron spectroscopy (XPS). Metal free phthalocyanine together with its zinc and copper congeners self-assembles into right-handed helical arrangements in a stack of phthalocyanine chromophores according to the CD spectroscopic result, while the nickel complex does so into the left-handed helical arrangements. These helical arrangements, acting as elemental primary structures, further pack in a hierarchical fashion into either highly ordered right-handed fibrous nanostructures with average 300 μm length, 4.8 μm width, and 4.4 μm helical pitch for 1 and 300 μm length, 2.4 μm width, and 1.8 μm helical pitch for 2 but left-handed fibrous nanostructures with average 4 μm length, 0.48 μm width, and 0.12 μm helical pitch for 3 and 300 μm length, 2 μm width, and 1.2 μm helical pitch for 4, clearly revealing the effect of central metal ion on the distance and relative orientation of neighboring phthalocyanine chromophores and in turn the supramolecular chirality, morphology, dimension, and handedness of the self-assembled nanostructures. The present result not only represents a unique phenomenon in the self-assembly of phthalocyanine compounds but more importantly denotes the transcription and amplification of molecular chirality to supramolecular helicity with different helical bias during the self-assembly processes without changing the chiral handles attached to the phthalocyanine chromophore.