Multistimuli-Responsive Squaraine Dyad Exhibiting Concentration-Controlled Vapochromic Luminescence

Stimuli-responsive organic materials with controllable luminescence are of enormous importance because of their potential applications in sensing, data security, and display devices. In this study, a multistimuli-responsive squaraine dyad (SQ-d) composed of two rigid squaraine moieties and a flexible ethylene linker was rationally designed and synthesized. SQ-d exhibits polymorphic luminescence, which can be reversibly switched by various external stimuli, including solvent vapor exposure, heat, and shear force. Unexpectedly, the weakly luminescent phase (O1) of SQ-d exhibits concentration-controlled vapochromic behavior. Film O1 can convert to a highly green-emissive phase (G1) under a low concentration of CHCl3 vapor and convert to a highly yellow-emissive phase (Y) under a high concentration of CHCl3 vapor; these originate from two distinct crystallization-induced emission enhancement processes. To the best of our knowledge, this is the first investigation of the effect of vapor concentration on the phase transitions of organic vapochromic luminophores. By analyzing the single-crystal structures and photophysical properties of SQ-d, we concluded that the green and yellow emissions probably originated from a zigzag stacking mode and an H-type π–π stacking mode, respectively. Finally, two prototypes based on SQ-d for applications in information encryption and vapor sensing were successfully demonstrated.具有可控发光性能的刺激响应型有机材料，因在传感、数据安全与显示器件等领域具备潜在应用价值而备受重视。本研究中，研究人员合理设计并合成了一种由两个刚性方酸菁（squaraine）单元与柔性亚乙基连接基组成的多刺激响应型方酸菁二元体（SQ-d）。SQ-d 表现出多晶型发光特性，可通过多种外部刺激（包括溶剂蒸气暴露、加热与剪切力）实现可逆切换。出乎意料的是，SQ-d 的弱发光晶型（O1）表现出浓度依赖型气致变色行为。在低浓度三氯甲烷（CHCl3）蒸气氛围下，O1薄膜可转变为高绿色发光晶型（G1）；而在高浓度CHCl3蒸气氛围下则转变为高黄色发光晶型（Y），上述两种转变分别源于两种截然不同的结晶诱导发光增强过程。据我们所知，本研究首次探究了蒸气浓度对有机气致变色发光材料相转变的影响。通过解析SQ-d的单晶结构与光物理性能，我们推断其绿色与黄色发光分别源自锯齿状堆积模式与H型π-π堆积模式。最后，本研究成功构建了两款基于SQ-d的原型器件，分别应用于信息加密与蒸气传感领域。