A chemically unlocked binary molecular switch

Abstract

A highly luminescent and sensitive terbium complex of a ligand comprising of a phthalimide group appended to a DO3A moiety is an active pH sensor that is conditional on its previous pH.

Sensitized terbium(iii) macrocyclic-phthalimide complexes as luminescent pH switches

“…Design and synthesis of ligands L 1a -L 4a and their corresponding Tb(III) complexes Our first design, reported earlier, 8 was based on the use of the well-known macrocyclic moiety DO3A, conjugated with a phthalimide chromophore via a propyl-bridge: 1,4,7-tris(carboxymethyl)-10-(3-[ phthalimide]propyl)-1,4,7,10-tetraazacyclododecane (L 1a , Scheme 1). Intermediate L 1 incorporated a DO3A-tert butyl ester structure as a protected chelator function, and an N-propylphthalimide function as the chromophore.…”

“…[3][4][5] Luminescent sensors based on lanthanide ions are known to have various advantages over purely organic systems stemming from the unique photophysical properties of these f-block elements. 6,7 For example, the lanthanide ion Tb(III) is known to exhibit long-lived (∼ms) excited states 8 and distinctive linelike emissions at long wavelengths (450-650 nm), 9 which offer an advantage over most shorter-lived (∼sub-μs) light scattering from organic chromophores yielding detection of analytes at extremely low concentrations. [10][11][12] However, like all lanthanide ions, Tb(III) must be excited indirectly via non-radiative energy transfer as f-f transitions themselves are Laporte forbidden, 13 giving rise to weak molar extinction coefficients (typically 1-10 M −1 cm −1 ) for the free unbound ions.…”

“…[16][17][18][19] Several lanthanide containing species, normally Eu(III) complexes or the generally more luminescent Tb(III) systems, have been employed as pH dependent molecular switches. 8,[20][21][22] Recent reports have shown various examples of pH switches in systems possessing sensitizing antenna conjugated to the DO3A moiety. 23, 24 Parker and Gunnlaugsson showed their phenanthridine- [25][26][27] and naphthalene-based 28,29 lanthanide complexes, which are switched on under basic conditions.…”

“…16,30,[34][35][36] Recently we reported an active molecular switch involving a ligand derived from a phthalimide chromophore conjugated to a DO3A moiety complexed to Tb(III): a system which was activated under basic conditions. 8 A systematic study on the effect of pH on the luminescent properties of lanthanide complexes using such macrocyclic-phthalimide ligands has not been reported to date. It is known that a phthalimide unit undergoes facile hydrolysis at pH 9-10 yielding an irreversible phthalamate-based system, 37,38 and we reasoned that this could be exploited, deriving a pH-dependent exclusion of water from the lanthanide centre as a result of the extra carboxylate donor so formed.…”

Photophysics of metal complexes

“…Moreover, the complex perform logic functions with luminescent pH response conditional in the pH to which is was previously exposed. 184 Eu(III) and Tb(III) complexes containing ligands of the form (mesityl) 2 B-p-C 6 H 4 -CO 2…”