A new rhodamine-based chemosensor 1 with a six-membered spirocyclic ring has been synthesized, which exhibits excellent pH stability and shows selective “turn-on” fluorescent detection of Cu²⁺ ions over a series of other metal ions including Cu⁺ ions. The expansion of spirocycle improves the stability and selectivity of the chemosensors in sensing of metal ions. Till today only few rhodamine structures R1–R5 with thiourea-, hydrazine amide-, or pyrrole-decorated six-membered spirocyclic rings are known that exhibit metal-ion sensing via C–N bond cleavage of the spiro ring. In this context, rhodamine compound that responds to the metal ion through C–C bond cleavage of the six-membered spiro ring is completely unknown. The present example is a first-time report that demonstrates selective sensing of Cu²⁺ ions through C–C bond cleavage over the conventional existing systems in the literature. The chemosensor 1 is cell permeable and can detect Cu²⁺ in live cells using confocal microscopy in the biologically relevant pH range with high photostability.

中文翻译：

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通过CC键断裂选择性感应Cu ^2+的新型六元pH不敏感若丹明螺环及其在细胞成像中的应用

合成了具有六元螺环的新型基于罗丹明的化学传感器1，该传感器具有出色的pH稳定性，并且对包括Cu ⁺离子在内的一系列其他金属离子显示出对Cu ²⁺离子的选择性“开启”荧光检测。螺环的扩展提高了化学传感器在金属离子感测中的稳定性和选择性。到今天为止，只有很少的罗丹明结构R1 - R5已知带有硫脲，肼酰胺或吡咯修饰的六元螺环的环通过螺环的C–N键断裂显示出金属离子感测。在这种情况下，通过六元螺环的CC键断裂对金属离子作出反应的若丹明化合物是完全未知的。本示例是首次报告，该报告演示了通过文献中常规现有系统通过C–C键断裂对Cu ²⁺离子的选择性感测。化学传感器1是可渗透细胞的，并且可以使用共聚焦显微镜在生物学相关的pH范围内以高光稳定性检测活细胞中的Cu ²⁺。