In xanthene dyes the upper aryl moiety is often a benzene ring, but in this work an L-shaped dibenzoxanthene dye (4) was synthesized with a five-membered (benz)imidazole ring as the upper aryl moiety. Although 4 was designed with the π-face of the dibenzoxanthene and the π-plane of the aryl moiety as coplanar, the reactivity of the compound at the triaryl carbon was quite high and easily attacked by solvent, such as methanol. The consequent discoloration is caused not only by the external exposure of the triaryl carbon, but also by the greatly reduced LUMO level and increased reactivity to nucleophilic attack when the π-system of the xanthene ring is expanded. The introduction of the 2,6-dimethylphenyl group was found to be effective to avoid nucleophilic attack by solvent. A compound, labeled 9c, with a 2,6-dimethylphenyl group as the aryl moiety, had sufficient stability to solvent, an emission maximum at 828 nm in DMF, and a fluorescence quantum yield of 8%.


中文翻译：

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基于荧光素开发近红外荧光染料的另一种方法

在x吨染料中，上部芳基部分通常是苯环，但在这项工作中，合成了L型二苯并氧杂蒽染料（4 ），其中五元（苯并）咪唑环作为上部芳基部分。虽然4被设计成与二苯并氧杂和芳基部分如共面的π共平面的π共面，在三芳基碳的化合物的反应性是相当高的，并通过溶剂容易受到攻击，例如甲醇。随之而来的变色不仅是由于三芳基碳的外部暴露引起的，而且是由于by吨环的π系统扩展时，LUMO含量大大降低以及对亲核攻击的反应性增强而引起的。2,6-dim的介绍发现乙基苯基可有效避免溶剂的亲核攻击。具有2,6-二甲基苯基作为芳基部分的标记为9c的化合物对溶剂具有足够的稳定性，在DMF中在828 nm处有最大发射，并且荧光量子产率为8％。