Tetraphenylethylene-Based Nanogels by Physical Encapsulation Technology: An AIEgen Transparent Film Thermometers

AIEgens have attracted intensive interest because of the unusual fluorescence feature. Although AIEgen-based materials have been developed for responding to the diverse ex-stimuli, such as mechano-, electro-, and thermal-stimuli, the practical application of AIEgen-based thermoluminescence is hampered for the following reasons: (1) high cost attributed to the complicated chemical modification, (2) low contrast and responsiveness resulting from the chromophoric property of the thermal functional group. In this contribution, a facile encapsulation technology-based strategy without any chemical modifications is developed to form the encapsulated TPE nanogels for the preparation of the AIEgen-based thermoluminescence. Thanks to the coexistence of the liquid and solid phases, the nanogel-based AIEgens can not only attain the transparent feature but also a reversible transformation between the single-molecule and aggregated state by ex-thermal stimuli. In the nanogel, the two aggregated states of TPE molecules are observed that result from being tangled by poly-TPGDA and from being self-assembled, respectively. Furthermore, the nanogels prepared at different temperatures demonstrate the controllable fluorescence intensity. The higher preparation temperature results in more aggregated TPE and higher fluorescence intensity. Finally, the nanogels are easily formed into the transparent film thermometers because of their flowability, which shows a switchable and stable fluorescence by ex-thermal stimuli. The transparent film thermometer demonstrates high potential in anticounterfeiting technology and biological imaging.