Abstract Azobenzene (azo) has attracted tremendous attention on solar thermal fuels on account of controllable energy storage and release. However, it remains great challenge to realize the light-induced rapid heat output due to the limited structure transformation. Herein, we synthesized two kinds of azo compounds (T-Azo, F-Azo) with different alkyl chains. The compounds combine multiple functions, reversible phase (solid-to-liquid) transition and trans-cis isomerization, to realize optically controllable heat release at room temperature. Compared with the F-Azo (8.2 °C), the relatively short-chain T-Azo obviously decreases to −6.3 °C in crystallization temperature after trans-to-cis isomerization due to weak molecular interaction. The F-Azo releases photo-thermal energy and phase-change enthalpy reaching a high energy density of 198.4 J g−1, which is 16% higher than that of T-Azo (170.5 J g−1). The IR thermal imaging camera shows that the temperature difference of F-Azo attains 2.1 °C at room temperature (25 °C) under the illumination of blue light (420 nm). This work puts an insightful understanding of controlling photo-thermal energy by phase change and photoisomerization.

中文翻译：

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烷基接枝的偶氮苯分子通过相变和光异构化的整合功能用于光致储热和释放

摘要 偶氮苯（azo）由于能量储存和释放可控，在太阳能热燃料方面引起了极大的关注。然而，由于有限的结构转变，实现光诱导的快速热输出仍然是一个巨大的挑战。在此，我们合成了两种不同烷基链的偶氮化合物（T-Azo、F-Azo）。该化合物结合了多种功能，可逆相（固-液）转变和反顺式异构化，在室温下实现光学可控的放热。与 F-Azo (8.2 °C) 相比，由于分子相互作用较弱，在反式到顺式异构化后，相对短链的 T-Azo 的结晶温度明显降低至 -6.3 °C。F-偶氮释放光热能和相变焓，达到 198.4 J g-1 的高能量密度，比 T-Azo (170.5 J g-1) 高 16%。红外热像仪显示，在室温（25°C）蓝光（420 nm）照射下，F-Azo的温差达到2.1°C。这项工作对通过相变和光异构化控制光热能提供了深刻的理解。