Taking advantages of intramolecular motion of D-A based aggregation-induced emission (AIE) molecular rotors and one-dimensional (1D) polymer fibers, highly sensitive optical fiber sensors that respond to ambient humidity rapidly and reversibly with observable chromatic fluorescence change are developed. Moisture environments induce the swelling of the polymer fibers, activating intramolecular motions of AIE molecules to result in red-shifted fluorescence and linear response to ambient relative humidity (RH). In this case, polymer fiber provides a process-friendly architecture and a physically tunable medium for the embedded AIE molecules to manipulate their fluorescence response characteristics.
Intramolecular motions of AIE molecules driven by ambient humidity. D-A based AIE molecules contain three segments: an electron-donating tetraphenylethene (TPE) group, an electron-accepting pyridinium salt unit, and a spacer unit of single (TPE-P)/double (TPE-EP) bond. The highly twisted TPE group with four phenyl rings ensures the intramolecular twisted-motion in the solid state, while intramolecular rotation of D-A subgroups based on the twisted intramolecular charge-transfer (TICT) effect achieves local polarity sensing. Combining AIE and TICT effects that manipulated by the intramolecular motions, a sensitive humidity sensor is developed by embedding AIE molecules into a water-captured polymer.
Dry spinning AIE/polymer microfiber sensor. Dry-spinning technology is utilized to fabricate AIE/polymer microfibers, and polyvinylpyrrolidone (PVP) is chosen as a material support. AIE/PVP micro-fibrous film shows chromatic fluorescence response and linear response to ambient humidity, serving as sensitive woven fabrics for spatial-temporal humidity mapping. Assembly of microfibers and UV silicone tube could be integrated to develop fiber-shaped flexible device, which can act as a built-in sensor for easy identification of RH and also be able to serve as color-tunable lighting for smart displays.
Electro-spinning AIE/polymer nanofiber sensor. Polyacrylic acid (PAA) nanofibers from electro-spinning characterized with large surface area, high porosity, and fine flexibility, are used as a physical medium for AIE molecules to achieve instant humidity response sensitivity. The nanofibrous nonwoven membranes show ultrafast response and recovery (< 1 s) to a neglectable amount of water, which can be applied as axial positioning interface for future integrated wearable systems.
The mechanism of intramolecular motion of AIE molecules has been demonstrated for developing highly sensitive AIE/polymer fiber sensor. The fluorescence response performance is amplified by refining the fiber structure and changing the chemical structure of polymers. Additionally, fibrous sensors can be used to build various architectures, facilitating multifunctionality in terms of spatial humidity mapping, high device-integration capability, and touchless positioning. The strategy of combining AIE and 1D fiber structure will not only provide a new route for humidity sensor, but also serve as artificial nerves to sense wide environmental stimuli.
This research received funding from the Fundamental Research Funds for the Central Universities, the National Natural Science Foundation of China, the Science and Technology Commission of Shanghai Municipality, the National Key Research and Development Program of China, the Program for Changjiang Scholars and Innovative Research Team in University, and International Joint Laboratory for Advanced Fiber and Low-Dimension Materials.
See the article:
Yunmeng Jiang, Yanhua Cheng*, Shunjie Liu, Haoke Zhang, Xiaoyan Zheng, Ming Chen, Michidmaa Khorloo, Hengxue Xiang, Ben Zhong Tang*, and Meifang Zhu*
Solid-state intramolecular motions in continuous fibers driven by ambient humidity for fluorescent sensors
Natl Sci Rev 2020; doi: 10.1093/nsr/nwaa135
The National Science Review is the first comprehensive scholarly journal released in English in China that is aimed at linking the country's rapidly advancing community of scientists with the global frontiers of science and technology. The journal also aims to shine a worldwide spotlight on scientific research advances across China.