α‑Monoacylated and α,α′- and α,β′-Diacylated Dipyrrins as Highly Sensitive Fluorescence “Turn-on” Zn2+ Probes

With the purpose of developing readily synthesized CHEF (chelation-enhanced fluorescence) type Zn2+ probes with relatively simple molecular structures and excellent sensing behavior, p-anisoyl chloride was used for the acylation of 5-(penta­fluoro­phenyl)­dipyrro­methane. Interestingly, the α,β′-diacylated product PS2 with a unique substitution mode was obtained in high yield in addition to the normal α-substituted mono- and diacylated products PS1 and PS3. Further oxidation of PS1–PS3 afforded dipyrrins S1–S3. Crystal structure and 1H NMR measurements of S2 demonstrate the existence of a pure tautomer, which is consistent with DFT calculations. S1–S3 show highly Zn2+ selective “turn-on” fluorescence based on a CHEF mechanism by the formation of 2:1 (probe:metal) Zn2+ complexes. The emission colors can be easily tuned from green to red by changing the dipyrrin substitution modes. Furthermore, these probes demonstrate fast responses and wide applicable pH ranges. Among them, S2 shows the highest Zn2+ sensitivity, with a detection limit of 4.4 × 10–8 M.

为开发具有相对简单分子结构与优异传感性能、易于合成的螯合增强荧光（CHEF，chelation-enhanced fluorescence）型Zn²+探针，本研究以对茴香酰氯对5-（五氟苯基）二吡咯甲烷进行酰化反应。有趣的是，除得到常规的α位单酰化与二酰化产物PS1、PS3外，还以高产率获得了具有独特取代模式的α,β′-二酰化产物PS2。对PS1~PS3进行进一步氧化反应，即可得到二吡咯烯类化合物S1~S3。对S2的晶体结构与氢谱（¹H NMR）表征结果证实其存在单一互变异构体，该结果与密度泛函理论（DFT，Density Functional Theory）计算结果相符。S1~S3可通过形成2:1（探针:金属）型Zn²+配合物，基于CHEF机制实现对Zn²+的高选择性“点亮”型荧光响应。通过改变二吡咯烯的取代模式，可便捷地将发射颜色从绿色调控至红色。此外，该系列探针还展现出响应迅速、适用pH范围广的特性。其中，S2对Zn²+的传感灵敏度最高，检出限可达4.4×10⁻⁸ mol/L。