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

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·L1a–Tb·L3a 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·L1b–Tb·L3b. Emission of phthalamate-based macrocyclic Tb(III) complexes Tb·L1b–Tb·L3b 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·L1b 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.

Luminescence Properties of Self-Aggregating TbIII-DOTA-Functionalized Calix[4]arenes

“…This points to a better protection of the Tb III ion from non-radiative deactivations in the case of the monomers. An increase of Tb-luminescence lifetimes occurs upon exclusion of water molecules from the first coordination sphere of the metal ion (Murru et al, 1993 ; Chen et al, 2013 ). In our case, a possible explanation of the shortening of luminescence lifetimes found for the micellar Tb III -DOTA-functionalized calix[4]arenes could be an enhanced cross-relaxation between Tb III ions and the formation of a more defined second coordination sphere around the micelle consisting of water molecules clustered via hydrogen bonds.…”

Water-Soluble Polymeric Probes for the Selective Sensing of Mercury Ion: pH-Driven Controllable Detection Sensitivity and Time

“…Similarly, the carboxylic acid has a tendency to be converted into a carboxylate (sodium salt) at high pH above the p K a value of P3 . If transition or lanthanide metal cations are added to this solution, they will replace sodium and form metal complexes because the carboxylate anion has more affinity toward transition or lanthanide metal cations than the sodium cation. − As shown in Figure , during the addition of Hg 2+ ion into low pH (below p K a ) solutions, the dithioacetal group can easily be deprotected by Hg 2+ ion with the assistance of the CO···Hg coordination interaction, leading to fast sensing of Hg 2+ ions. In the case of high pH (above p K a ) solutions, mercaptopropionic acid would be expected to be fully ionized and exist as a carboxylate anion with which Hg 2+ ions can preferentially form −COO – Hg 2+ –OOC– ion complexes in the beginning.…”

Fluorescent Rotary Switches: Four- vs Three-Substituted Phthalimide Boron Difluoride Schiff Base Complexes

“…The molecular design of fluorescent materials plays a crucial role in their photoluminescence performance and applications. Phthalimide fluorophores find a broad range of applications in photonics and biomedical technology, and they exhibit very good fluorescence quantum yields in solution and solid state, covering the blue-green-red spectral region. − Due to the strong electron-accepting nature of the imide ring, they have a low-lying LUMO level, which allows tuning of the emission by environmental polarity, substitution pattern of the phthalimide ring, and nature of substituents. ,− Upon photoexcitation, electron-donating substituents at the 4- or 3-position cause photoinduced intramolecular or twisted charge transfer, resulting in broad-range emission. ,,,− Phthalimide-based molecular or supramolecular complexes are important functional materials in photonics, − ,,,, bioimaging, , photodynamic therapy, ,, organic light-emitting diodes, and sensor ,, technology. Until now, only a few papers have reported on the boron difluoride phthalimide-based complexes and their photoluminescence properties, which exhibit good quantum yields in the blue-green spectral region. ,− Boron dipyrromethene (BODIPY) − and boron difluoride hydrazone (BODIHY) dyes are attracting increasing research interest due to their very good photoluminescence properties coupled with an aggregation-induced emission phenomenon that allows tuning of absorption/emission bands covering all visible spectral range.…”