Understanding the role of conjugation length on the self-assembly behaviour of oligophenyleneethynylenes

Multi-Emission Carbon Dots Combining Turn-On Sensing and Fluorescence Quenching Exhibit Ultrahigh Selectivity for Mercury in Real Water Samples

Mercury is a ubiquitous heavy-metal pollutant and poses serious ecological and human-health risks. There is an ever-growing demand for rapid, sensitive, and selective detection of mercury in natural waters, particularly for regions lacking infrastructure specialized for mercury analysis. Here, we show that a sensor based on multi-emission carbon dots (M-CDs) exhibits ultrahigh sensing selectivity toward Hg(II) in complex environmental matrices, tested in the presence of a range of environmentally relevant metal/metalloid ions as well as natural and artificial ligands, using various real water samples. By incorporating structural features of calcein and folic acid that enable tunable emissions, the M-CDs couple an emission enhancement at 432 nm and a simultaneous reduction at 521 nm, with the intensity ratio linearly related to the Hg(II) concentration up to 1200 μg/L, independent of matrix compositions. The M-CDs have a detection limit of 5.6 μg/L, a response time of 1 min, and a spike recovery of 94 ± 3.7%. The intensified emission is attributed to proton transfer and aggregation-induced emission enhancement, whereas the quenching is due to proton and electron transfer. These findings also have important implications for mercury identification in other complex matrices for routine, screening-level food safety and health management practices.

Oligo(phenyleneethynylene)s: Shape-Tunable Building Blocks for Supramolecular Self-Assembly

Oligo(phenyleneethynylene)s (OPEs) have attracted widespread attention due to their remarkable (opto)electronic and photophysical properties, which have enabled numerous applications. The versatile functionalization possibilities of OPEs make them unique candidates to form various shape-persistent geometries, including linear, triangular, rectangular, hexagonal and macrocyclic. However, as a result of this structural variety, it is oftentimes challenging to correlate molecular design with self-assembly properties. In this minireview, we have classified OPEs based on their molecular shapes and correlated them with their self-assembly behavior in solution. Particularly, we provide important insights into the aggregation propensity of the different molecular shapes and how to tune the association strength using various non-covalent interactions. Our classification will enable a better understanding of the structure-property correlation in OPEs, which is key to develop supramolecular functional materials.

Isoindigo-Based Dual-Acceptor Conjugated Polymers Incorporated Conjugation Length and Intramolecular Charge Transfer for High-Efficient Photothermal Conversion

Photothermal tumor therapy (PTT) and photoacoustic imaging (PA) have emerged as promising noninvasive diagnostic and therapeutic approaches for cancer treatment. However, the development of efficient PTT agents with high photostability and strong near-infrared (NIR) absorption remains challenging. This study synthesizes three isoindigo-based dual-acceptor conjugated polymers (CPs) (P-IIG-TPD, P-IIG-DPP, and P-IIG-EDOT-BT) via a green and nontoxic direct arylation polymerization (DArP) method and characterizes their optical, electrochemical, and NIR photothermal conversion properties. By incorporating two acceptors into the backbone, the resulting polymers exhibit enhanced photothermal conversion efficiency (PCE) due to improved synergy among conjugation length, planarity, and intramolecular charge transfer (ICT). The nanoparticles (NPs) of P-IIG-EDOT-BT and P-IIG-DPP have a uniform size distribution around 140 nm and exhibit remarkable NIR absorption at 808 nm. In addition, P-IIG-EDOT-BT and P-IIG-DPP NPs exhibit high PCEs of 62% and 78%, respectively. This study promotes the molecular design of CPs as NIR photothermal conversion materials and provides guidance for the development of novel dual-acceptor CPs for tumor diagnosis and treatment.

Anticooperative Supramolecular Oligomerization Mediated by V-Shaped Monomer Design and Unconventional Hydrogen Bonds

After more than three decades of extensive investigations on supramolecular polymers, strategies for self-limiting growth still remain challenging. Herein, we exploit a new V-shaped monomer design to achieve anticooperatively formed oligomers with superior robustness and high luminescence. In toluene, the monomer-oligomer equilibrium is shifted to the monomer side, enabling the elucidation of the molecular packing modes and the resulting (weak) anticooperativity. Steric effects associated with an antiparallel staircase organization of the dyes are proposed to outcompete aromatic and unconventional B-F⋅⋅⋅H-N/C interactions, restricting the growth at the stage of oligomers. In methylcyclohexane (MCH), the packing modes and the anticooperativity are preserved; however, pronounced solvophobic and chain-enwrapping effects lead to thermally ultrastable oligomers. Our results shed light on understanding anticooperative effects and restricted growth in self-assembly.

Self-assembled organic and hybrid materials derived from oligo-(p-phenyleneethynylenes)

Oligo-(p-Phenyleneethynylenes) (OPEs) have garnered widespread interest over the past three decades due to their excellent opto-electronic properties. However, the chief focus has been on the use of mainly small molecules or polymeric systems for the study of their structural diversity in opto-electronic applications. Recently, researchers have started delving deeper into their utility in material applications. Purely organic materials such as supramolecular polymers, self-assembled nanostructures, nanostructured organogels and single-crystalline materials derived from OPEs have already been developed and researched. Chirality has also been introduced into these systems. Additionally, these have shown physical properties such as polymorphism, liquid crystallinity, melt formation, mechanochromism, etc. All these materials have also shown excellent luminescence properties with high quantum yield and some have even shown energy harvesting properties. There have also been sporadic reports on OPE linker based hybrid systems such as metallogels and metal-organic framework (MOF) structures where structural analysis reveals the origin of tunable emission in these materials. Furthermore, by innovative structural design, unexplored properties of OPEs such as water repellency, bioimaging, drug delivery, photocatalysis, energy transfer, nanomorphology control, photoconductivity, and colour tunability could be achieved. This feature article will, therefore, encompass a detailed discussion on the development of this field as well as the analysis of the properties realized in OPE derived self-assembled supramolecular materials. The main focus will be on the following classes of materials: soft supramolecular materials, crystalline supramolecular π-systems, nanoscale metal-organic frameworks (NMOFs) and bulk metal-organic frameworks (MOFs) and how their application horizon has been expanded by integrating OPEs into their structures.

Odd-Even Effect on Supramolecular Co-Assemblies: Control over the Two-Dimensional Self-Assemblies of a Fluorenone Derivative with Asymmetrically Substituted Alkyl Chains

The precise control of two-dimensional supramolecular co-assemblies presents a research topic related to advance nanotechnology. Here, we report a scanning tunneling microscopy (STM) study of the mixture behavior of three fluorenone derivatives at the liquid-solid interface. The target molecule is F-C₁₂C₁₃ whose structure bears asymmetrical alkyls, whereas the regulating molecules, either F-C₁₂C₁₂ or F-C₁₃C₁₃, are structurally symmetric. By STM imaging of systematic mixtures with various volumes among the sample solutions, we found that the mixing ratio mainly determined the binary outcomes. Compared with F-C₁₂C₁₂, F-C₁₃C₁₃ shows a stronger ability to dominate the patterning, explained by the larger binding and adsorption energies calculated by the force field simulations. Moreover, the odd-even effect exists in the system. Overall, we acquired knowledge about the regulating ability of bi-component supramolecular assembling, especially for structurally asymmetric molecular systems.

Precise Synthesis of π-Conjugated Block Copolymers and Polymerization-Induced Chiral Self-Assembly toward Helical Nanofibers with Circularly Polarized Luminescence

Precise synthesis and efficient self-assembly of semiconducting polymers are of great interest. Herein, we report the controlled synthesis of π-conjugated poly(phenyl isocyanide)-b-poly(phenyleneethylene) (PPI-b-PPE) copolymers via chain extension of ethynyl 4-iodobenzene initiated by Pd(II)-terminated helical poly(phenyl isocyanide) (PPI). The in-situ-generated block copolymers self-assembled into various supramolecular architectures depending on the PPE length. The helical PPI segment induced the block copolymers with an appropriate PPE length self-assemble into helical nanofibers with a controlled size and defined helicity. Interestingly, the chiral assemblies of the block copolymers exhibit intense optical activity and emit clear circularly polarized luminescence.