Bright Blue‐Emitting Ce³⁺ Complexes with Encapsulating Polybenzimidazole Tripodal Ligands as Potential Electroluminescent Devices

Abstract

The versatile photophysical properties of lanthanide ions [1] have inspired vigorous research activities owing to a wide range of potential applications in the fields of bioassays, [2] sensor systems, [3] and optical materials. [4] The Eu 3+ and Tb 3+ ions are of particular interest owing to their long luminescence lifetime and narrow emission bands in the visible region. Some other lanthanide ions were also investigated for their near-infrared luminescence or diagnostic properties. [5] Recently, the electroluminescence of lanthanide ions has attracted increasing attention as potential light-emitting materials in light-emitting diodes (LEDs), and a number of Eu 3+ and Tb 3+ complexes have been incorporated into LED devices.[6] Compared with other lanthanide ions, the Ce 3+ ion is unique, characteristic of parity-allowed electric-dipole 4f! 5d transitions, which lead to fast decay times and high light outputs. [7] Great endeavors have been devoted to doping Ce 3+ ions into inorganic crystals to serve as metal phosphors with possible applications in solid-state lasers, quantum cutters, inorganic scintillators, and fluorescent lamps and displays. [7] By contrast, investigations of the luminescence properties of Ce 3+ ion in organic coordination environments remain rather rare, although that of the free Ce 3+ ion has been thoroughly studied [8] and its luminescence in Ce 3+ halides, organometallics, and polymer films has been studied. [9] It is well known that although the inner 4f orbitals of Ce 3+ are well shielded, their 5d orbitals are very sensitive to the ligand sphere. Many organic ligands have been found to quench Ce 3+ luminescence upon complexation, and contact of Ce 3+ ions with solvent molecules may engender nonradiative transitions to diminish the luminescence.[8] Nevertheless, studies have indicated that diazapolyoxabicyclic ligands (cryptands) could well shield the Ce 3+ ions and result in efficient luminescence in the ultraviolet region.[10] Some Ce 3+ complexes containing halide anions and certain carboxylate groups were also found to be luminescent, and the emission bands were remarkably red-shifted into the visible region up to 630 nm depending on the interactions of the 5d energy levels with the crystal field. [9,11] These findings suggest that, in principle, highly luminescent Ce 3+ complexes are achievable provided that a suitable organic ligand is designed to encapsulate the Ce 3+ ion. More important, as the ligand can be readily modified and decorated to provide an adjustable crystal field, the use of the Ce 3+ chromophore in luminescent materials can potentially offer tunable emission wavelength and strength, covering the UV and Vis regions. [7][8][9][10][11] Taking into account the well-studied red-emitting Eu 3+ complexes and green-emitting Tb 3+ complexes in LEDs, luminescent Ce 3+ complexes may provide an alternative as light-emitters in LED devices, in contrast with the commonly studied inorganic systems. [12] We and others [13] have studied lanthanide complexes with tripodal...

Crystal structure of (4-(1H-imidazol-5-yl)benzoic acid-κN) (4-(1H-imidazol-5-yl)benzoato-κN)silver(I), C20H15N4O4Ag

“…The organic linkers with N and O donors often have been employed as e ective building blocks in the construction of MOFs [5][6][7]. For example, the N-containing heterocyclic ring ligands including substituted tetrazole, imidazole, benzimidazole, 1,2,4-triazole have been extensively used to construct interesting MOFs [8][9][10]. On the other hand, carboxylate ligands play an important role in coordination chemistry, which may adopt diverse binding modes such as monodentate, chelating, and bridging con gurations.…”

Crystal structure of catena-poly[aqua-µ-1,4-benzenedicarboxylato-κ2O:O'-3,5-dimethyl-4-phenyl-1,2,4-triazole-κN-zinc(II)] monohydrate, Zn(H2O)(C8H4O4)(C10H11N3)·H2O, C18H17N3O6Zn

“…The rational design and construction of novel metal-organic frameworks (MOFs) are of current interest in the field of crystal engineering not only because of their promising applications in gas storage, separation, luminescence, heterogeneous catalysis and ion exchange, but also owing to their intriguing molecular architectures and topologies [1][2][3][4]. Generally, the multidentate organic ligands containing coordination sites of N donors such as triazole have favourable coordinate abilities and are widely utilized as building blocks in the construction of MOFs.…”

A new lanthanum(III) complex containing acetylacetone and 1H-imidazole

“…From the viewpoint of high luminescence efficiency, the luminescence based on the f-d transition of Ce 3+ is quite promising due to its allowed electronic transition. However, the emission of Ce 3+ in metalorganic complexes have been reported only occasionally, for example, in [Ce(triRNTB) 2 ](CF 3 SO 3 ) 3 [NTB = N-substituted tris(N-alkylbenzimidazol-2-ylmethyl)amine] and 1 3 [Ce(Im) 3 -(ImH)]ÁImH (Zheng et al, 2007;Meyer et al, 2015). One of the reasons for this is the difficulty of retaining a certain distance between Ce 3+ ions in order to avoid luminescence quenching caused by energy transfer between Ce 3+ ions.…”