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Solid-Emission-Tunable Squaraine with Thermal-Promoted Aggregate-State Transitions for Fast Thermal History Sensing
Liming Yang1, Engui Zhao2, Guan Wang1
1Beijing Advanced Innovation Center for Soft Matter Science and Engineering, State Key Laboratory of Chemical Re-source Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
Abstract:
Determining thermal history is crucial in many industrial processes, but reliable and sensitive organic thermal history indicators are currently absent. Herein, we report on the development of a squaraine-based fluorescent molecule, DPEA-SQ, for the detection of thermal exposure histories up to 436 K. DPEA-SQ forms multiple single crystals (DPEA-SQ-I, DPEA-SQ-II, and DPEA-SQ-III) with different conformations and aggregate-state packing modes, contributing to their different fluorescence wavelengths, lifetimes, and efficiencies. Interestingly, DPEA-SQ-I and DPEA-SQ-III undergo aggregate-state structural transitions to form the thermodynamically more stable DPEA-SQ-II, which are accompanied by changes in their fluorescence. By taking advantage of similar aggregate-state structural transformations during heating, a high-temperature thermal exposure history of up to 436 K is recorded and reflected by their fluorescence. To demonstrate the potential practical applications of DPEA-SQ, a DPEA-SQ-Powder/PDMS film is prepared and coated on an electric circuit board, which enables real-time monitoring of localized overheating by the naked eye. Additionally, the fluorescence peaks of DPEA-SQ-Powder and DPEA-SQ-Powder/PDMS films remain unchanged after storage at 373 K for 52 days, demonstrating high aggregate-state stability. The fast and reliable responses of this system make it an excellent candidate for the detection of overtemperature traces in electronic components and circuit diagnosis.
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