Sensitized terbium (III) macrocyclic-phthalimide complexes as luminescent pH switches
Author(s)
Author(s)
Chen, G.
Wardle, N. J.
Sarris, J.
Chatterton, N. P.
Date Issued
2013
Publisher
Royal Society of Chemistry
Journal
Dalton Transactions
Volume
42
Issue
39
Start page
14115
End page
14124
Abstract
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·L1a1a–Tb·L3a3a 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·L1b1b1b–Tb·L3b3b3b. Emission of phthalamate-based macrocyclic Tb(III) complexes Tb·L1b1b1b–Tb·L3b3b3b 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·L1b1b 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.
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