Construction of Helically Stacked π‐Electron Systems in Poly(quinolylene‐2,3‐methylene) Stabilized by Intramolecular Hydrogen Bonds

Facile End-Functionalization of Poly(Quinolylene-2,3-Methylene) Using the Terminal Palladium Complex: Thiocarbonylation through Formation of an Acyl Palladium Complex at the Polymer Terminal

The end-functionalization of poly(quinolylene-2,3-methylene)s (PQM) via thiocarbonylation is successfully achieved by forming an acyl palladium complex. The terminal palladium complex of the PQMs synthesized by living cyclocopolymerization of o-allenylaryl isocyanide is quantitatively converted to a tractable acyl palladium complex through the carbon monoxide insertion into a palladium-carbon bond. The resulting acyl palladium complex exhibits high reactivity toward thiols, thereby enabling the introduction of various substituents at the ω-chain end of PQM by selectively converting them to thioester groups. The one-pot procedure enables the arbitrary control of both terminal structures of PQMs, including the synthesis of multi-armed block copolymers and a triblock polymer. Additionally, the resulting thioester groups can serve as reactive sites and be converted into amide groups using amines. The new end-functionalization method has the potential to be applied not only to the synthesis of PQM but also to other polymerization reactions using transition-metal complexes, and can lead to a wide range of developments in polymer synthesis.

Stability Enhancement of a π-Stacked Helical Structure Using Substituents of an Amino Acid Side Chain: Helix Formation via a Nucleation-Elongation Mechanism

Molecular design involving the incorporation of an α-amino acid residue into the side chain or main chain of a polymer is often used to stabilize artificial molecular architectures through intramolecular hydrogen bonding. However, this molecular design strategy rarely considers the importance of interactions between substituents at the α-position of amino acid moieties, as found in nature. Herein, we report the synthesis of a novel series of π-stacked helical poly(quinolylene-2,3-methylene) with amino acid derivatives bearing different substituents at the α-position. We found that the thermal stability of π-stacked helical poly(quinolylene-2,3-methylene) is significantly improved by packing the substituents in the empty spaces between the side chains. In particular, when a bulky cyclohexyl alanine derivative was used as the side chain, the π-stacked helical structure maintained its stability even in dimethylsulfoxide, a hydrogen bond competitor. The stabilization of the π-stacked structure by the amino acid substituents resulted in a unique polymerization behavior involving nucleation-elongation steps. In the case of derivatives with leucine and cyclohexyl alanine, which form stable π-stacked helical structures, metastable structures with entangled main chains were formed in the initial polymerization stage. These structures subsequently underwent an irreversible structural change to achieve a thermodynamically stable helical π-stacked conformation as a nucleus for subsequent polymerization. Thereafter, the polymerization reaction proceeded with the elongation of the π-stacked helical structure. Differences in the stability of these systems indicated that the amino acid substituents on the side chains determine the most thermodynamically stable π-stacked helical structure.

Modular engineering of gold-silver nanocluster supermolecular structure endow strong electrochemiluminescence for ultrasensitive bioanalysis

Here, the gold-silver nanocluster supramolecular network (AuAg NCs) is synthesized by the assembly of Au nanoclusters (Au NCs) and Ag NCs via host-guest complexation between 6-aza-2-thiothymine as the stabilizer of Au NCs and L-arginine as the stabilizer of Ag NCs in solution, whose electrochemiluminescence (ECL) emission is not only exceptionally stronger than that of discrete monometallic NCs, but also more significant than that of agminated monometallic NCs. The dramatically enhanced ECL emission of self-assembled AuAg NCs originates from the synergistic effect of aggregation-induced enhancement and silver effect in gold catalysis. As a proof of concept, the self-assembled AuAg NCs is successfully applied in the ultrasensitive detection of breast cancer biomarker microRNAs-21 (miR-21), which guides a new pathway for creating high-quality nano-optical elements in chemical sensors, biological imaging, and lightemitting devices.

Visible colorimetric dosimetry of UV and ionizing radiations by a dual-module photochromic nanocluster

Radiation dosimeters displaying conspicuous response of irradiance are highly desirable, owing to the growing demand of monitoring high-energy radiation and environmental exposure. Herein, we present a case of dosimetry based on a discrete nanocluster, [Th6(OH)4(O)4(H2O)6](TPC)8(HCOO)4∙4DMF∙H2O (Th-SINAP-100), by judiciously incorporating heavy Th6 polynuclear centers as radiation attenuator and organic linkers as photo-responsive sensor. Interestingly, dual-module photochromic transitions upon multiple external stimuli including UV, β-ray, and γ-ray are integrated into this single material. The striking color change, and more significantly, the visible color transition of luminescence in response to accumulating radiation dose allow an on-site quantitative platform for naked-eye detection of ionization radiations over a broad range (1-80 kGy). Single crystal X-ray diffraction and density functional theory calculations reveal that the dual-module photochromism can be attributed to the π(TPC) → π*(TPC) intermolecular charge transfer driven by enhanced π-π stacking interaction between the adjacent TPC moieties upon irradiation.

Achieving UV and X-ray Dual Photochromism in a Metal-Organic Hybrid via Structural Modulation

Rational design and synthesis of new photochromic sensors have been active research areas of inquiry, particularly on how to predict and tailor their properties and functionalities. Herein, two thulium 2,2':6',2''-terpyridine-4'-carboxylate (TPC)-functionalized metal-organic hybrids, Tm(TPC)₂(HCOO)(H₂O) (TmTPC-1) and Tm(TPC)(HCOO)₂ (TmTPC-2) with different photochromic response behaviors, have been successfully prepared, allowing for straightforward investigations of the structure-property correlation. Single-crystal X-ray diffraction and electron paramagnetic resonance analyses revealed that the incorporation of a unique dangling decorating TPC unit in TmTPC-1 offers a shorter and more accessible π-π interaction pathway between the adjacent TPC moieties than that in TmTPC-2. Such a structural feature leads to the production of radical species via a photoinduced intermolecular electron-transfer (IeMCT) process upon UV or X-ray irradiation, which ultimately endows TmTPC-1 with a rather unusual UV and X-ray dual photochromism. A linear relationship between the change of UV-vis absorbance intensity and X-ray dose was established, making TmTPC-1 a promising dosimeter for X-ray radiation with an extremely high energy threshold (30 kGy). To advance the development for real-world application, we have fabricated polyvinylidene fluoride (PVDF) membranes incorporating TmTPC-1 for functioning either as a UV imager or as an X-ray radiation indicator. Lastly, TmTPC-1 exhibits high thermal stability (up to 400 °C) and radioresistance (at least 900 kGy), and also excellent reversibility of photochromic transformation (at least 5 cycles).

Synthesis and properties of helically-folded poly(arylenediethynylene)s

Three arylenediethnylene-based helical foldamers having pyridine, naphthaleneimide and pyrene cores show unique conformational changes and photophysical properties in various organic solvents.

Highly 2,3-selective and fast living polymerization of alkyl-, alkoxy- and phenylallenes using nickel(ii) catalysts

A novel Ni(ii) catalyst was developed to initiate the polymerization of various allene monomers efficiently in a fast and living/controlled manner, and the thermodynamic and crystallization properties of the polymers were investigated.

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.