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

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posted on 07.06.2013, 00:00 authored by Yubin Ding, Xin Li, Tong Li, Weihong Zhu, Yongshu Xie
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 PS1PS3 afforded dipyrrins S1S3. Crystal structure and 1H NMR measurements of S2 demonstrate the existence of a pure tautomer, which is consistent with DFT calculations. S1S3 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.