Excimer Disaggregation Enhanced Emission: A Fluorescence “Turn-On” Approach to Oxoanion Recognition

Abstract

A new approach to anion sensing that involves excimer disaggregation induced emission (EDIE) is reported. It involves the anion-mediated disaggregation of the excimer formed from a cationic macrocycle. This leads to an increase in the observed fluorescence intensity. The macrocycle in question, cyclo[1]N 2,N 6-dimethyl-N 2,N 6-bis­(6-(1H-imidazolium-1-yl)­pyridin-2-yl)­pyridine-2,6-diamine­[1]­1,4-dimethylbenzene (1 2+; prepared as its PF6 – salt), is obtained in ca. 70% yield via a simple cyclization. X-ray diffraction analyses of single crystals revealed that, as prepared, this macrocycle exists in a supramolecular polymeric form in the solid state. Macrocycle 1 2+ is weakly fluorescent in acetonitrile. The emission intensity is concentration dependent, with the maximum intensity being observed at [1 2+] ≈ 0.020 mM. This finding is ascribed to formation of an excimer, followed possibly by higher order aggregates as the concentration of 1 2+ is increased. Addition of tetrabutylammonium pyrophosphate (HP2O7 3–) to 1 2+ (0.020 mM in acetonitrile) produces a ca. 200-fold enhancement in the emission intensity (λex = 334 nm; λem = 390–650 nm). These findings are rationalized in terms of the HP2O7 3– serving to break up essentially non-fluorescent excited-state dimers of 1 2+ through formation of a highly fluorescent anion-bound monomeric complex, 1 2+·HP2O7 3–. A turn-on in the fluorescence intensity is also seen for H2PO4 – and, to a lesser extent, HCO3 –. Little (HSO4 –, NO3 –) or essentially no (N3 –, SCN–, F–, Cl–, Br– and I–) response is seen for other anions. Solid-state structural analysis of single crystals obtained after treating 1 2+ with HP2O7 3– in the presence of water revealed a salt form wherein a H2P2O7 2– anion sits above the cone-like macrocycle.

Advances in fluorescent and colorimetric sensors for anionic species

“…31d. Sessler, Gong and co-workers reported the first example of oxoanion sensing using excimer disaggregation induced emission (EDIE) [94]. Macrocycle 40, comprised of two "halves" (one half consisting of three pyridine moieties and the other a bis-imidazolium system), was found to form excimer aggregates in acetonitrile which had notably poor fluorescence.…”

Cyclometalated iridium(iii) complex of a 1,2,3-triazole-based ligand for highly selective sensing of pyrophosphate ion

“…, imidazolium and thiazolium). 37–42 The C–H bond of 1,2,3-triazole can act as an amine bond surrogate unit for detecting anions due to the electronegativity of three nitrogen atoms of the ring in the triazole unit and an enormous dipole situated toward the triazole C–H bond exerted by the lone pair of nitrogen atoms. 43–46 Further, the acidity of triazole C–H proton strengthens on coordinating the triazole nitrogen with the metal center, thus promoting the binding ability of this C–H toward anions.…”

Subtle Structural Changes of Dyes Lead to Distinctly Different Fluorescent Behaviors in Cellular Context: The Role of G-Quadruplex DNA Interaction Using Coumarin–Quinazolinone Conjugates as a Case Study

“…The cellular environment which is full of biologically relevant species may interact with dyes and induce dye disaggregation to recover fluorescence . In the past years, the aggregation–disaggregation sensing mechanism or disaggregation-induced emission (DIE) has been applied for multiple bioanalyte sensing, including small biomolecules, , biomacromolecules such as proteins, − and others. , Thus, understanding the photoluminescent behaviors of dyes in a cellular context is particularly important.…”