Sensitized terbium(iii) macrocyclic-phthalimide complexes as luminescent pH switchesElectronic supplementary information (ESI) available: 1H NMR study on kinetics of hydrolysis of LaL1a. See DOI: 10.1039/c3dt51236c

Four new macrocyclic-phthalimide ligands were synthesised via the coupling of N -(3-bromopropyl)phthalimide either to cyclen (1,4,7,10-tetraazacyclododecane) itself or its carboxylate-functionalized analogues, and photophysical studies were carried out on their corresponding Tb( iii ) complexes in aqueous media as a function of pH. Luminescence intensities of Tb·L 1a -Tb·L 3a were in ' switched off ' mode under acidic conditions (pH < 4), and were activated on progression to basic conditions as the phthalimido functions therein were hydrolysed to their corresponding phthalamates Tb·L 1b -Tb·L 3b . Emission of phthalamate-based macrocyclic Tb( iii ) complexes Tb·L 1b -Tb·L 3b was in ' switched on ' mode between pH 4 and 11, exhibiting high quantum yields ( Φ ) and long lifetimes ( τ ) of the order of milliseconds at pH ∼ 6. Tb( iii ) emissions were found to decline with increasing number of chromophores. The values of Φ and τ were 46% and 2.4 ms respectively for Tb·L 1b at pH ∼ 6 when activated. This is the best pH-dependent sensor based on a Tb( iii ) complex reported to date, benefiting from the macrocyclic architecture of the ligand. Four new macrocyclic-phthalimide ligands were synthesised and photophysical studies were carried out on their corresponding Tb(III) complexes in aqueous media as a function of pH.