Colorless polyimide (CPI) is a key material of flexible displays characterized by high thermal stability and flexibility. However, it is susceptible to photodegradation induced by ultraviolet (UV) light exposure in its operating environments, thus necessitating the development of a new UV absorber to address this issue. Meanwhile, the high-temperature processing required for CPI synthesis makes the development of novel UV absorbers challenging. Here, we developed a novel thermally stable and highly soluble star-shaped trimeric UV absorber compatible with CPI. Various hydroxyphenyl benzotriazoles (HBTs) were designed to explore molecular structure dependent changes in thermal stability and solubility that are changed following molecular trade-offs between planarity and distortion. HBTs were synthesized by substituting them on a central phenyl linker to obtain 3 dimers (-PBT-PBT, and -PBT) and 1 trimer (TPBT). UV/VIS spectroscopy, computational calculation, solubility test, thermalgravimetric analysis, and powder X-ray diffraction result supported the molecular structure-dependent changes in optical absorption, solubility, thermal stability, and crystallinity. Interestingly, among the synthesized UV absorbers, a star-shaped trimer TPBT with optimized distortion and planarity exhibited great solubility (>8 wt% in NMP solvent) and outstanding thermal stability (1 wt% loss at 360 °C). Furthermore, due to its strong UV absorption characteristics, the TPBT efficiently prevented the photodegradation of CPI film after xenon lamp irradiation. This study highlights the key roles of tailoring trade-offs in molecular planarity and distortion to develop thermally stable and highly soluble UV absorbers for CPI films.

中文翻译：

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用于无色聚酰亚胺薄膜的热稳定且高度可溶的紫外线吸收剂：星形羟基苯基苯并三唑，在分子平面度和畸变之间进行定制权衡

无色聚酰亚胺（CPI）是柔性显示器的关键材料，具有高热稳定性和柔韧性。然而，它很容易受到工作环境中紫外线 (UV) 光照射引起的光降解，因此需要开发一种新的紫外线吸收剂来解决这个问题。同时，CPI合成所需的高温处理使得新型紫外线吸收剂的开发具有挑战性。在这里，我们开发了一种与 CPI 兼容的新型热稳定且高度可溶的星形三聚紫外线吸收剂。设计了各种羟基苯基苯并三唑（HBT）来探索热稳定性和溶解度的分子结构依赖性变化，这些变化随着平面性和变形之间的分子权衡而变化。通过在中心苯基连接体上取代 HBT 来合成 HBT，以获得 3 个二聚体（-PBT-PBT 和 -PBT）和 1 个三聚体（TPBT）。 UV/VIS 光谱、计算计算、溶解度测试、热重分析和粉末 X 射线衍射结果支持分子结构依赖性的光吸收、溶解度、热稳定性和结晶度变化。有趣的是，在合成的紫外线吸收剂中，具有优化变形和平面度的星形三聚体TPBT表现出巨大的溶解度（在NMP溶剂中> 8 wt%）和出色的热稳定性（360°C时损失1 wt%）。此外，由于TPBT具有较强的紫外吸收特性，有效防止了氙灯照射后CPI薄膜的光降解。这项研究强调了在分子平面度和畸变方面进行权衡的关键作用，以开发用于 CPI 薄膜的热稳定和高度可溶的紫外线吸收剂。