A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

希夫碱凝胶因子的合成及压致变色性能研究

智能凝胶作为一种新型软材料对外界刺激具有独特的响应性,近年来受到人们的极大关注。以易于结构衍生化的2,4-（3,4-二氯苯亚甲基）-D-葡萄糖酸甲酯为平台分子,设计合成了新型智能希夫碱类凝胶因子化合物3a和3b。研究了凝胶因子在不同溶剂中的凝胶性能,并探索了机械力对于智能凝胶因子的影响。结果表明,凝胶因子的凝胶能力依赖于溶剂的种类和凝胶因子碳链的长度;通过原子力显微镜及场发射透射电镜可以观察到凝胶呈三维纤维网状结构。有趣的是,碳链较短的化合物3b具有压致变色性能,场发射扫描电镜和X-射线衍射表明压致变色是由于结晶态和无定型态聚集体结构的转变。     

Expanding the Horizon of Mechanochromic Detection by Luminescent Shear Stress Sensor Supraparticles

Novel sensor particles have been developed that expand the variety of today's mechanochromic systems. The developed supraparticles consist of several different components to enable the sensor function. First, a luminescence‐quenching core material is coated with silica nanoparticles. Second, this structure is surrounded by raspberry‐like nanostructured silica particles, which host luminophore moieties. Upon shear stress, components spatially separated in the original supraparticles, namely quencher and luminophore components, come into contact. This causes an irreversible quenching of the luminescence (sensor turn‐off). Different options to select core, quencher, and luminophore components allow to drive the sensors to different sensing options regarding response time, sensitivity, and operation time. The sensors can be sensitive and rapid in response or generated to monitor the influence of shear stress over longer periods of time. Thus, a rapid, visible, “on‐the‐fly” sensing of shear stress is possible as well as monitoring the impact of prolonged shear stress. The particles are assembled by spray‐drying. This affords flexibility when choosing the type of quencher and luminophore moiety. As such, the sensitivity of this robust, particle‐based shear stress sensor system can be deliberately configured. Furthermore, the supraparticle sensor can be integrated in surfaces to create interactive, communicating materials.     

A Hierarchical Nanoparticle‐in‐Micropore Architecture for Enhanced Mechanosensitivity and Stretchability in Mechanochromic Electronic Skins

Biological tissues are multiresponsive and functional, and similar properties might be possible in synthetic systems by merging responsive polymers with hierarchical soft architectures. For example, mechanochromic polymers have applications in force‐responsive colorimetric sensors and soft robotics, but their integration into sensitive, multifunctional devices remains challenging. Herein, a hierarchical nanoparticle‐in‐micropore (NP‐MP) architecture in porous mechanochromic polymers, which enhances the mechanosensitivity and stretchability of mechanochromic electronic skins (e‐skins), is reported. The hierarchical NP‐MP structure results in stress‐concentration‐induced mechanochemical activation of mechanophores, significantly improving the mechanochromic sensitivity to both tensile strain and normal force (critical tensile strain: 50% and normal force: 1 N). Furthermore, the porous mechanochromic composites exhibit a reversible mechanochromism under a strain of 250%. This architecture enables a dual‐mode mechanochromic e‐skin for detecting static/dynamic forces via mechanochromism and triboelectricity. The hierarchical NP‐MP architecture provides a general platform to develop mechanochromic composites with high sensitivity and stretchability.     

透明光子晶体薄膜的力致变色调控及防伪应用

利用SiO2胶体粒子构筑三维蛋白石光子晶体阵列,并将其嵌入聚二甲基硅氧烷（PDMS）弹性体内,制备了一种具有力致变色性能的透明光子晶体薄膜。采用SEM、光纤光谱仪、数码相机等对光子晶体薄膜进行了结构、光学性能的表征,并研究了其在防伪中的应用。结果表明：施加拉力时,该透明光子晶体薄膜显现结构色,并随拉伸量的增加发生持续蓝移,撤销拉力可逆回复至初始状态,且即使经历100次循环拉伸,光子晶体薄膜依旧保持稳定的光学性能。将光子晶体薄膜进行图案化设计,通过施加或撤销拉力可使隐藏于其中的图案快速显现或消失,在防伪领域具有广阔的应用前景。