Scheme 1 (A) Tetraphenylethylene-bismaleimide (TPE–M2) and the “on/off” switch via photoinduced electron transfer (PET) by maleimides. If both maleimides participate in Diels-Alder, the PET effect is absent and the TPE group becomes emissive. The Diels-Alder reaction is reversed by heat and results in fluorescence quenching again. (B) The structure and components used in furan-maleimide systems containing TPE. The on/off effect of TPE by reversible crosslinking in the matrix is depicted.#

Fig.1 Overview of aggregation-induced emission by TPE–FMA, measured at an excitation wavelength of 385 nm. (A) The fluorescence emission of TPE–FMA solutions (100 µM concentration) as a function of v/v acetonitrile/water solvent ratio expressed as percentage of water. The insets are pictures of the solutions taken under a 365 nm excitation lamp. (B) Tetraphenylethylene-bismaleimide (TPE–M2) and TPE–FMA in powder form, illustrating the fluorescence quenching mechanism. (C) Dynamic light scattering results of TPE–FMA in a fluorescent 90% H2O solution at a concentration of 100 µM.#

实验验证涵盖模型化合物的溶液相AIE分析，以及不同交联密度薄膜（低交联F3BM与高交联F6BM）的固态荧光演化测试。采用共聚焦显微镜评估探针在微米尺度上的均匀性，借助荧光光谱仪（采用385 nm激发波长以规避光致褪色）与示差扫描量热法（DSC）分析热可逆性。实验结果表明：共聚焦图像证实TPE–M2在聚合物基质中呈微米级均匀分散；DSC测试表明微量探针的加入未改变材料的玻璃化转变温度与逆狄尔斯-阿尔德反应热行为；在115°C–120°C下加热2.5分钟引发逆狄尔斯-阿尔德反应后，荧光几乎完全熄灭，降至室温后随着交联恢复，荧光强度完全复原，且5次加热-冷却循环后未出现性能衰退。动力学模拟与荧光强度的拟合表明，归一化荧光强度与狄尔斯-阿尔德反应转化率呈现幂律指数为 6.7–6.8 的强非线性关系（$I \propto X^n$），相比理论预测的二次方依赖，这种高阶响应极大地提升了对固化后期微小交联度变化的检测灵敏度。

Fig.2 Fluorescence intensity at an excitation wavelength of 385 nm. (A) F3BM scaffolds and (B) F6BM scaffolds, as a function of tetraphenylethylene (TPE) incorporation. The indicated percentage is expressed as the molar percentage of TPE-bismaleimide (TPE–M2) with respect to BMI–689. One sample was prepared in bulk (F3BM) and measured in the same experimental setup, as discussed in the next section. The inset images are taken under an ultraviolet (UV) excitation wavelength of 366 nm, measured with an optical fiber.#

Fig.3 Confocal microscopy images and corresponding bright-field images of F3BM (top) and F6BM systems (bottom) containing a varying wt% of tetraphenylethylene-bismaleimide (TPE–M2), measured 25 µm below the surface.#

Fig.4 Fluorescence recovery recorded after quenching at 120°C for 2.5 min by leaving the material at 60°C for an hour, followed by curing at room temperature. (A) F3BM-0.5% and (B) F6BM-0.5%. The full recovery (cycle 2) was measured three days after the heating step.#

Fig.5 (A) The measured temperature during the fluorescence reversion procedure, including two images of the thermal camera. (B) Simulated maleimide conversion within the network using kinetic parameters based on literature values [35]. (C) Normalized photoluminescence intensity plotted versus the conversion of the Diels-Alder system. The data are fitted using an empirical fitting equation that takes into account background fluorescence (x = conversion, y = fluorescence intensity).#

Fig.6 Differential scanning calorimetry results of (A) F3BM and (B) F6BM containing a varying amount of tetraphenylethylene-bismaleimide (TPE–M2). The second cycle is displayed, which was measured at a heating rate of 10°C min−1. The raw data are shown, and the graphs were not horizontally translated. The first cycle is included for both systems in the Supporting information (Figure S24).#

Fig.7 The effect of heating and cooling cycles on the relative fluorescence for (A) F3BM-0.5% and (B) F6BM-0.5%. (C) A comparison of the maximum and minimum fluorescence intensity at 370 nm. (D) Overview of the hot-writing principle, where relative differences in fluorescence intensity can be observed after writing, under excitation with a long-range ultraviolet (UV) lamp (385 nm).#

研究的完整执行流程包含探针与多官能团单体合成、薄膜铸造与固化、热刺激-光学光谱循环测试以及动力学方程求解。除光谱与动力学指标外，研究还通过热刻写实验进行了局部热历史跟踪与自修复示范：使用热刻写笔在材料表面局部加热可瞬间熄灭荧光并“写入”文字（如“TPE”），在室温下放置一周后由于交联自发恢复，文字完全消退。这证明了该方法对局部热历史及自修复过程具备极佳的原位空间分辨跟踪能力。