Self-assembled bright luminescent hierarchical materials from a tripodal benzoate antenna and heptadentate Eu(III) and Tb(III) cyclen complexes

Abstract

The europium heptadentate coordinatively unsaturated (Eu(III)) and the terbium (Tb(III)) 1,4,7,10tetraazacyclododecane (cyclen) complexes 1 and 2 were used in conjunction with ligand 3 (1,3,5-benzene-trisethynylbenzoate) to form the supramolecular self-assembly structures 4 and 5; this being investigated in both the solid and the solution state. The resulting self-assemblies gave rise to metal centered emission (both in the solid and solution) upon excitation of 3, confirming its role as a sensitizing antenna. Drop-cased examples of ligand 3, and the solid forms of 4 and 5, formed from both organic and mixture of organic-aqueous solutions, were analyzed using Scanning Electron Microscopy, which showed significant changes in morphology; the ligand giving rise to one dimensional structures, while both 4 and 5 formed amorphous materials that were highly dense solid networks containing nanoporous features. The surface area (216 and 119 m 2 $g -1 for 4 and 5 respectively) and the ability of these porous materials to capture and store gases such as N 2 investigated at 77 K. The self-assembly formation was also investigated in diluted solution by monitoring the various photophysical properties of 3-5. This demonstrated that the most stable structures were that consisting of a single antennae 3 and three complexes of 1 or 2 (e.g., 4 and 5) in solution. By monitoring the excited state lifetimes of the Eu(III) and Tb(III) ions in H 2 O and D 2 O respectively, we showed that their hydration states (the q-value) changed from ~2 to 0, upon formation of the assemblies, indicating that the three benzoates of 3 coordinated directly to the each of the three lanthanide centers. Finally we demonstrate that this hierarchically porous materials can be used for the sensing of organic solvents as the emission is highly depended on the solvent environment; the lanthanide emission being quenched in the presence of acetonitrile and THF, but greatly enhanced in the presence of methanol.

Lanthanide-based MOFs: synthesis approaches and applications in cancer diagnosis and therapy

“…41,42 Savyasachi and coworkers reported a strategy for the assembly of Eu(III) and Tb(III) cyclen-based heptadentate complexes and ligand 1,3,5-benzene-trisethynylbenzoate. 43 The binding ability and flexible structure of ligands make it available for the formation of Ln-based MOFs. The Eu-MOFs and Tb-MOFs were synthesized via a microwave-assisted solvothermal method.…”

Tuning the Doping of Europium in Gadolinium Borate Microparticles at Mesoscale Toward Efficient Production of Red Phosphors

“…1−5 For instance, light-emitting diodes (LEDs) based on the use of rare-earth-doped phosphors have been widely recognized as a green lighting source in favor of energy saving and environment protection. 6−9 In such a module, phosphors play crucial roles in determining the performance and quality of LEDs and the fast development of LED raises the demand of phosphors with uniform size distribution, high luminescence quantum efficiency, and high thermal stability. 10 Typically, the phosphors are made up of host materials and activators, while their optical properties are extremely sensitive to their structures in mesoscale.…”

“…The rare-earth-doped luminescent nanoparticles and microparticles have found many applications, and the rare-earth ions with emission in every color are revolutionizing applications from lighting devices to television displays. − For instance, light-emitting diodes (LEDs) based on the use of rare-earth-doped phosphors have been widely recognized as a green lighting source in favor of energy saving and environment protection. − In such a module, phosphors play crucial roles in determining the performance and quality of LEDs and the fast development of LED raises the demand of phosphors with uniform size distribution, high luminescence quantum efficiency, and high thermal stability . Typically, the phosphors are made up of host materials and activators, while their optical properties are extremely sensitive to their structures in mesoscale. − The host materials include nitrogen/oxide, aluminate, , silicate, borate, and fluorides .…”