Na Zhang's research while affiliated with Nanjing Institute of Technology and other places

The mechanochromic materials can respond to environmental changes by altering the optical properties of the system, which has garnered significant attention in recently. The utilization of these materials for the purpose of sensing tensile and compressive stress has been extensively documented. However, the mechanochromic polymer that can effectively discriminate hardness of inorganic particles is still rarely reported. In this article, a force‐sensitive organic polysiloxane was developed by introducing triethenyl‐substituted rhodamine derivatives crosslinker into the polymethylhydrosiloxane network through hydrosilylation addition reaction. The results demonstrated that the grinding of the crosslinked polysiloxane effectively facilitated the transmission of external force to the polymeric network, leading to an open ring isomerization of rhodamine accompanied by significant alterations in visible and fluorescent color. In addition, we found that the optical properties of the system showed distinct variations when the inorganic particles with different Moh's hardness were co‐ground with the polysiloxane. High Moh's hardness particles, such as Al 2 O 3 , could effectively trigger the mechanochromic behavior of the polymer, while Na 2 SO 4 particles with low hardness failed to induce the corresponding change. Therefore, this organic polysiloxane could be used as a potential fluorescent indicator for hardness recognition.

Shape memory polymer (SMP) can store entropic energy during programming and release the energy as recovery. The released energy is determined by the recovery strain and the recovery stress. The low recovery stress of SMP limits its application. In this paper, shape memory nanocomposite fibers (SMNFs) prepared by wet spinning through a two‐step orientating process show thermo‐active and water‐driven shape memory effect. Carbon nanotubes (CNTs) are uniformly dispersed in SMNF and aligned along the SMNF axis. SMNF with 13 wt% CNT has an average maximum recovery stress of ~160 MPa at 100°C, which is almost five times higher than that of a pure PVA fiber. The uniform distribution of the orientational CNTs in the SMNFs and the confinement effect of the CNTs confirmed by the increased relaxation time contribute to the increment of the recovery stress. Aligned CNTs impede the mobility of amorphous chains and increase the T g of SMNFs. The twisted SMNF can drive an object up to 25 times its own weight in water to rotate and lift. The rotational velocity of the twisted SMNF is sensitive to temperature. Water molecules acting as plasticizers greatly enhance the mobility of the PVA chains, and the SMNF in water releases the stored entropic energy at room temperature. The SMNF with high recovery stress demonstrates its potential for applications in the field of actuators and artificial muscles.

The incorporation of mechanophores, motifs that transform mechanical stimulus into chemical reaction or optical variation, allows creating materials with stress-responsive properties. The most widely used mechanophore generally features a weak bond, but its cleavage is typical an irreversible process. Here, we showed that this problem can be solved by folding—unfolding of a molecular tweezer. We systematically studied the mechanochromic properties of polyurethanes with cyano-substituted oligo(p-phenylene) vinylene (COP) tweezer (DPU). As a control experiment, a class of polyurethanes containing only a single COP moiety (MPU) was also prepared. The DPU showed prominent mechanochromic properties, due to the intramolecular folding-unfolding of COP tweezer under mechanical stimulus. The process was efficient, reversible and optical detectable. However, due to the disability to form either intramolecular folding or intermolecular aggregation, the MPU sample was mechanical inert.

We discovered the force induced strengthening of a mechanochromic polymer based on naphthalene fused cyclobutane mechanophore (NCD). Our results revealed that mechanical-induced retro-cycloaddition of the NCD and subsequent crosslinking reactions...

Pyrene-based hydrazone derivative (PYI) which was synthesized from 1-pyrene formaldehyde and isoniazid presented a mechanochromic (MC) behavior and self-recovery performance at room temperature. Mild grinding of a PYI crystal would convert its fluorescence from weak blue to yellow. The metastable grinded PYI powders could revert to the original stable state at room temperature (RT) in 24 h. However, under the same conditions, the control molecule PYB did not exhibit MC property. The results showed that the MC behavior of PYI was caused by mechanical induced slippage of the pyrene dimers in the lattice, which altered the stacking behavior and molecular interactions. Because the two pyrene units in PYB dimer almost exhibited a sandwich-type arrangement, mechanical stimulus had little influence on the stacking state of PYB. Therefore, it did not exhibit the MC property. In addition, when mixed with oxalic acid and malonic acid, the fluorescence of pristine PYI was turned off, meanwhile with a visible color change from yellow to orange red. The phenomenon was a result of enhanced ICT effect between acidifying pyridine and pyrene unit.

Mechanochromic polymers (MCPs), which response to mechanical stimuli by optical signal changing, are regarded to apply in smart materials such as force sensors. Although rapid progress in the MCPs have...

Designing fluorescent sensors for selective detection of CN⁻ in aqueous and even solid states are still rarely reported due to the aggregation-caused quenching (ACQ) effect. In this paper, we report a novel fluorescent probe C-1. Due to the AIE effect, C-1 displayed obvious orange-red fluorescence with emission peak centered at 597nm in aqueous solution and solid state. Under the influence of electron withdrawing cyano and ester groups, the vinyl C=C bond was easy to be attacked by nucleophilic CN⁻, which destroyed the conjugated bridge and also blocked the ICT process between the donor and the acceptor. The emission band shifted from 597 nm to 475 nm consequently. Other anions have no effect on the fluorescence of C-1. Thus, C-1 could be used as a selective CN⁻ sensor. The UV-visible and fluorescent measurement confirmed the interactions between C-1 and CN⁻. ¹H NMR titration method further demonstrated the detection mechanism. The sensitivity and detection limit of C-1 were measured to be 5.97 × 10⁴ M⁻¹ and 1.2 μM respectively. Due to the solid-state emission nature, C-1 immersed test strip was prepared and used as an effective test kit to detect CN¯ ion.

Among various two‐dimensional (2D) materials, organic 2D polymers have attracted much attention, owing to their specific properties, such as lightweight, good flexibility, adjustable structure, and high adaptability. In recent years, more and more scientists have devoted to the research on their structural design, synthesis, characterization, and potential properties. However, in contrast to traditional one‐dimensional (1D) and three‐dimensional (3D) network macromolecules, the synthesis of 2D structures presents a challenge to polymer chemists, because polymerization usually takes place in a spatially random manner in solution‐phase synthesis. In this review, we will focus on the synthesis methods of organic 2D materials, which have played a pivotal role since the beginning of the development of this field. We will highlight the representative examples according to the different types of polymers, including supramolecular organic 2D layers and covalent organic 2D polymers, and identify possible future research directions. 2D organic materials, which include supramolecular organic 2D layers and covalent organic 2D polymers have attracted extensive attention of scientists. The synthesis methods of organic 2D materials have played a pivotal role since the beginning of the development of this field. Supramolecular organic 2D layers can be formed by cross‐linking between structural units through noncovalent interactions and self‐assembly of polymers or small molecules. The preparation of independent covalent 2D polymers can be divided into three categories: “bottom–up” interfacial synthesis, “top–down” stripping synthesis and direct solution‐phase synthesis.

Among various fluorescent chemosensors based on different platforms, π-conjugated polymer-based sensors have attracted much attention, owing to their amplified detection sensitivity for the detection of a variety of environmental pollutants and bioactive compounds. Since the report of the first conjugated polymer sensor in the 90s, this sensing platform has reached more than two decades of progress, with an explosion of the research in this field observed in the last ten years. In this review, we will focus on the fluorescent polymer sensors with N-heterocyclic aromatic moieties, which have played a pivotal role since the beginning of the development of conjugated polymer-based fluorescence sensing strategy. We will highlight the representative examples according to the different type of heterocycles, illustrate the structure-property relationships, point out the limitations and challenges of current systems, and also identify possible future research directions.