Integration of the 1,2,3-Triazole "Click" Motif as a Potent Signalling Element in Metal Ion Responsive Fluorescent Probes

• Published in: Chemistry : a European journal 2013-02, Vol.19 (9), p.2990-3005
• Main Authors: Ast, Sandra, Fischer, Tobias, Müller, Holger, Mickler, Wulfhard, Schwichtenberg, Mathias, Rurack, Knut, Holdt, Hans-Jürgen
• Format: Article
• Language: English
• Subjects: Acetonitrile; charge transfer; Chemical compounds; Chemistry; click chemistry; Electron transfer; Fluorescence; fluorescent probes; Ions; Mathematical analysis; metal ions; Precursors; Receptors; Signalling
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201201575

In a systematic approach we synthesized a new series of fluorescent probes incorporating donor–acceptor (D‐A) substituted 1,2,3‐triazoles as conjugative π‐linkers between the alkali metal ion receptor N‐phenylaza‐[18]crown‐6 and different fluorophoric groups with different electron‐acceptor properties (4‐naphthalimide, meso‐phenyl‐BODIPY and 9‐anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge‐transfer (CT) type probes 1, 2 and 7, the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge‐separated states. In the presence of Na+ and K+ ICT is interrupted, which resulted in a lighting‐up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7, which contains a 9‐anthracenyl moiety as the electron‐accepting fluorophore, is the only probe which retains light‐up features in water and works as a highly K+/Na+‐selective probe under simulated physiological conditions. Virtually decoupled BODIPY‐based 6 and photoinduced electron transfer (PET) type probes 3–5, where the 10‐substituted anthracen‐9‐yl fluorophores are connected to the 1,2,3‐triazole through a methylene spacer, show strong ion‐induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3‐triazole fluoroionophores. Light up: Combination of a typical alkali‐metal ion receptor with various popular fluorophores in different signalling architectures through simple clicking of the modular precursors yields probes that integrate a new donor–acceptor‐substituted 1,2,3‐triazole motif, which gives rise to interesting absorption and fluorescence responses upon target binding.