Development of efficient unimolecular visible light photoinitiators (PIs) with photobleaching capabilities, which is essential for various biomedical applications and photopolymerization of thick materials, remains an emerging challenge. Based on the photochemistry of heteroaromatic compounds, unimolecular visible light oxime ester PIs (2-O, 2-S, 3-O, and 3-S), which contain coumarin derivatives as visible light chromophores, were designed and synthesized. Photophysical and photochemical properties of these PIs have been investigated using UV-Vis spectroscopy, fluorescence spectroscopy and electron spin resonance (ESR). The oxime-esters photolyse rapidly under 450 nm LED light irradiation, especially 2-S, and have good photobleaching capabilities. Also, we have, for the first time, shown that heterocyclic radicals efficiently initiate free radical polymerization of acrylate monomers. Notably, these photobleaching initiators can be used to induce thiol-based click photopolymerization to prepare materials with a thickness of up to 10 mm.

中文翻译：

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具有末端杂环部分的可裂解香豆素基肟酯：可光漂白的引发剂，用于在可见光照射下进行深层光固化

具有光漂白能力的高效单分子可见光光引发剂（PI）的开发对于各种生物医学应用和厚材料的光聚合必不可少，仍然是一个新兴的挑战。基于杂芳族化合物的光化学，设计并合成了包含香豆素衍生物作为可见光发色团的单分子可见光肟酯PIs（2-O，2-S，3-O和3-S）。已使用UV-Vis光谱，荧光光谱和电子自旋共振（ESR）研究了这些PI的光物理和光化学性质。肟酯在450 nm LED光照下迅速裂解，尤其是2-S，并具有良好的光漂白能力。同样，我们第一次表明，杂环基可以有效地引发丙烯酸酯单体的自由基聚合。值得注意的是，这些光致漂白引发剂可用于引发基于硫醇的点击光聚合，以制备厚度最大为10mm的材料。