A ratiometric fluorescent probe for magnesium employing excited state intramolecular proton transfer

A simple fluorescent sensor has been developed for the ratiometric recognition of Mg2+ in semi-aqueous solution at pH 7.0. The sensor, a Schiff base, undergoes Excited State Intramolecular Proton Transfer (ESIPT) to generate a keto tautomer with proficient Mg2+ binding capability. The sensor displays good selectivity over other metal ions including alkali/alkali earth ions and can measure Mg2+ ion concentration between 2.0 and 30.0 μM. The binding stoichiometry was established as 2:1 (host:guest) with an association constant (K21) of (1.4 ± 0.1) × 104 M−2. The sensor could potentially be used to detect conditions such as hypermagnesaemia.