AbstractRecent developments in materials showing photo-induced liquefaction and softening, including molecular materials, gels, and polymers, are described. A macrocyclic azobenzene molecule that has long alkoxy chains was first reported to show a photo-induced solid–liquid phase transition at room temperature through trans–cis photoisomerization. The structure–property relationship for understanding the photo-induced phase transition has since been investigated by using model compounds with a simple molecular design. Such azobenzene-based materials also exhibited dynamic motion on glass and water surfaces; these motions are driven by continuous liquefaction/crystallization and dissolution of the liquefied material. Photo-induced liquefaction has been further developed in middle molecular and polymeric materials. The effects of the alkyl chain length, functional groups, and number of azobenzene units on the photo-induced behavior have been extensively investigated. In addition, by using photoresponsive gelators, the photo-induced quasi-solid–liquid (gel–sol) phase transition of gels was accomplished. Moreover, very recently, a photoresponsive plasticizer that can plasticize “photo-inactive” polymers by light irradiation has been proposed.This review focuses on the recent developments on the photo-induced liquefaction and softening of azobenzene-based materials. The trans–cis photoisomerization of azobenzene units incorporated in molecular materials, polymers, and gels induces a variety of state changes such as solid–liquid, gel–sol, and glass–rubber transitions of those materials isothermally. Several novel applications such as reusable and environmentally friendly photoresists, reworkable adhesives, and self-healing materials can be expected using the photochemical liquefaction and softening.

中文翻译：

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分子材料、聚合物和相关化合物的光化学液化和软化

摘要描述了显示光致液化和软化的材料的最新进展，包括分子材料、凝胶和聚合物。首次报道了具有长烷氧基链的大环偶氮苯分子在室温下通过反式-顺式光异构化显示出光诱导的固-液相转变。此后，通过使用具有简单分子设计的模型化合物研究了用于理解光致相变的结构 - 性质关系。这种基于偶氮苯的材料在玻璃和水表面上也表现出动态运动；这些运动是由液化材料的连续液化/结晶和溶解驱动的。光致液化在中分子和聚合物材料中得到了进一步发展。烷基链长、官能团和偶氮苯单元数量对光诱导行为的影响已得到广泛研究。此外，通过使用光响应凝胶剂，实现了凝胶的光诱导准固-液（凝胶-溶胶）相变。此外，最近还提出了一种光敏增塑剂，它可以通过光照射使“光不活泼”聚合物增塑。本文重点介绍了偶氮苯基材料的光致液化和软化的最新进展。结合在分子材料、聚合物和凝胶中的偶氮苯单元的反式-顺式光异构化会引起各种状态变化，例如这些材料的等温固-液、凝胶-溶胶和玻璃-橡胶转变。