Bright lanthanide based probes for optical bioimaging must rely on the antenna principle, where the lanthanide-centred excited state is formed by a complex sensitization process. Efficient sensitization of lanthanide-centred emission occurs via triplet states centred on the sensitizing chromophore. Here, the triplet state of thioxanthone chromophores is modulated by extending the π-system. Three thioxanthone chromophores-thioxanthone, benzo[c]thioxanthone, and naphtho[2,3-c]thioxanthone were synthesised and characterised. The triplet state energies and lifetimes is found to change as expected, and two dyes are found to be suitable sensitizers for europium(iii) luminescence. Reactive derivatives of thioxanthone and benzo[c]thioxanthone were prepared and coupled to a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) lanthanide binding pocket. The photophysics and the performance in optical bioimaging of the resulting europium(iii) complexes were investigated. It is concluded that while the energetics favour efficient sensitization, the solution structure does not. While it was found that the complexes are too lipophilic to be efficient luminescent probes for optical bioimaging, we successfully demonstrated bioimaging using europium(iii) luminescence following 405 nm excitation.

中文翻译：

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π扩展的噻吨酮-在可见光激发下，设计基于镧系元素的发光探针的噻吨酮敏化剂的三重态水平。

用于光学生物成像的基于镧系元素的明亮探针必须依靠天线原理，其中以镧系元素为中心的激发态是通过复杂的敏化过程形成的。通过以致敏发色团为中心的三重态实现对镧系元素中心发射的有效敏化。在此，噻吨酮生色团的三重态通过扩展π系统来调节。合成并表征了三种噻吨酮生色团-噻吨酮，苯并[c]噻吨酮和萘[2,3-c]噻吨酮。发现三重态能量和寿命按预期改变，并且发现两种染料是适合（（iii）发光的敏化剂。制备了噻吨酮和苯并[c]噻吨酮的反应性衍生物，并将其偶联至1,4,7,10-四氮杂环十二烷-1,4，7-三乙酸（DO3A）镧系元素结合口袋。研究了所得euro（iii）配合物的光物理性质和光学生物成像性能。结论是，尽管高能学有利于有效的敏化，但溶液结构却并非如此。虽然发现该复合物亲脂性太高，无法用作光学生物成像的有效发光探针，但我们成功地证明了在405 nm激发后使用（（iii）发光进行生物成像。