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Water-soluble amino(ethanesulfonate) and [bis(ethanesulfonate)] anthracenes as fluorescent photoinduced electron transfer (PET) pH indicators and Fe3+ chemosensors

Lookup NU author(s): Dr Ulrich Baisch


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Two novel water-soluble anthracene-based fluorescent indicators appended with amino(ethanesulfonate) groups were designed and synthesised. A monoethanesulfonated or diethanesulfonate ligand is located in the proximity of a tertiary amino moiety separated by a methylene spacer at the 9-position of an anthracene fluorophore. The molecular structure of the monoethanesulfonated species was determined by single crystal X-ray diffraction. The molecules were studied by UV-visible absorption and fluorescence spectroscopy in water as molecular probes for protons and cations. The anthracene probes function according to a photoinduced electron transfer (PET) mechanism based on a 'fluorophore-spacer-receptor' format resulting in blue fluorescence on protonation. The excited state pK(a)* values were evaluated to be 5.7 and 7.4, respectively, for the di- and monoethanesulfonated anthracenes at a constant ionic strength of 0.1 M NaCl. The monoethanesulfonated indicator exhibits a high fluorescence quantum yield of 0.62 in acidic solution, and an enhancement factor (EF) of 9, while the diethanesulfonated indicator has a more modest fluorescence quantum yield of 0.17 and an EF of 2.4. Under acidic conditions both indicators are susceptible to selective quenching of the fluorescence by Fe3+ with linear responses between 0.6-8.9 mM and 0.3-5.0 mM Fe3+ for the diethanesulfonated and monoethanesulfonated anthracenes, respectively. The lack of a vertex in the Job's plots indicates no metal-ligand complexation suggesting the fluorescence quenching may be due to an inner filter effect from Fe3+ absorbance.

Publication metadata

Author(s): Cardona MA, Mallia CJ, Baisch U, Magri DC

Publication type: Article

Publication status: Published

Journal: RSC Advances

Year: 2016

Volume: 6

Issue: 5

Pages: 3783-3791

Print publication date: 06/01/2016

Online publication date: 06/01/2016

Acceptance date: 17/12/2015

ISSN (electronic): 2046-2069

Publisher: Royal Society of Chemistry


DOI: 10.1039/c5ra22341e


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Funder referenceFunder name
European Social Fund (ESF) under Operational Programme II - Cohesion Policy
University of Malta
CM1005European Cooperation in Science and Technology (COST Action)