Excitation-Dependent Photoluminescence Color Tuning in Lanthanide-Organic Hybrid Materials

One-Dimensional Organic-Inorganic Lead Bromide Hybrids with Excitation-Dependent White-Light Emission Templated by Pyridinium Derivatives

Organic-inorganic hybrid metal halides have attracted widespread attention due to their excellent tunability and versatility. Here, we have selected pyridinium derivatives with different substituent groups or substitution positions as the organic templating cations and obtained six 1D chain-like structures. They are divided into three types: type I (single chain), type II (double chain), and type III (triple chain), with tunable optical band gaps and emission properties. Among them, only (2,4-LD)PbBr₃ (2,4-LD = 2,4-lutidine) shows an exciton-dependent emission phenomenon, ranging from strong yellow-white to weak red-white light. By comparing its photoluminescence spectrum with that of its bromate (2,4-LD)Br, it is found that the strong yellow-white emission at 534 nm mainly came from the organic component. Furthermore, through a comparison of the fluorescence spectra and lifetimes of (2,4-LD)PbBr₃ and (2-MP)PbBr₃ (2-MP = 2-methylpyridine) with similar structures at different temperatures, we confirm that the tunable emission of (2,4-LD)PbBr₃ comes from different photoluminescent sources corresponding to organic cations and self-trapped excitons. Density functional theory calculations further reveal that (2,4-LD)PbBr₃ has a stronger interaction between organic and inorganic components compared to (2-MP)PbBr₃. This work highlights the importance of organic templating cations in hybrid metal halides and the new functionalities associated with them.

Brightly Luminescent (TbxLu1-x)2bdc3·nH2O MOFs: Effect of Synthesis Conditions on Structure and Luminescent Properties

Luminescent, heterometallic terbium(III)-lutetium(III) terephthalate metal-organic frameworks (MOFs) were synthesized via direct reaction between aqueous solutions of disodium terephthalate and nitrates of corresponding lanthanides by using two methods: synthesis from diluted and concentrated solutions. For (Tb_xLu_1-x)₂bdc₃·nH₂O MOFs (bdc = 1,4-benzenedicarboxylate) containing more than 30 at. % of Tb³⁺, only one crystalline phase was formed: Ln₂bdc₃·4H₂O. At lower Tb³⁺ concentrations, MOFs crystallized as the mixture of Ln₂bdc₃·4H₂O and Ln₂bdc₃·10H₂O (diluted solutions) or Ln₂bdc₃ (concentrated solutions). All synthesized samples that contained Tb³⁺ ions demonstrated bright green luminescence upon excitation into the ¹ππ* excited state of terephthalate ions. The photoluminescence quantum yields (PLQY) of the compounds corresponding to the Ln₂bdc₃ crystalline phase were significantly larger than for Ln₂bdc₃·4H₂O and Ln₂bdc₃·10H₂O phases due to absence of quenching from water molecules possessing high-energy O-H vibrational modes. One of the synthesized materials, namely, (Tb_0.1Lu_0.9)₂bdc₃·1.4H₂O, had one of the highest PLQY among Tb-based MOFs, 95%.

3-Pyridylacetic-Based Lanthanide Complexes Exhibiting Magnetic Entropy Changes, Single-Molecule Magnet, and Fluorescence

Four complexes from lanthanides, 3-pyridylacetate, and 1,10-phenanthroline, formulated as [Ln2(3-PAA)2(μ-Cl)2(phen)4](ClO4)2 [Ln = Gd(1), Dy(2), Eu(3), Tb(4), 3-PAA = 3-pyridylacetic acid, phen = 1,10-phenanthroline], were obtained. The four compounds were characterized by IR spectra, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1-4 are isomorphous, and they have a dinuclear structure. Magnetic studies reveal that 1 shows the magnetocaloric effect with -ΔS m max = 19.03 J kg-1 K-1 at 2 K for ΔH = 5 T, and 2 displays a field-induced single-molecule magnet with U eff = 19.02 K. The photoluminescent spectra of 3 and 4 exhibit strong characteristic emission, which demonstrate that the ligand-to-EuIII/TbIII energy transfer is efficient.

Dicarboxylate Modulating Molecular-Ionic Platinum Compounds with Variable Stacking and Photoluminescence

Under solvothermal conditions, 10 molecular-ionic platinum compounds [Pt(NIA)₂]·(L)·nH₂O (L = dicarboxylate) were synthesized. In the reaction, acetonitrile undergoes trimerization in situ to generate N-(1-iminoethyl)acetamidine (NIA), which coordinates to Pt^II ions in forming the N-(1-iminoethyl)acetamidine platinum cation, while the organic carboxylates act as anions. Structural analysis shows that carboxylate ligands regulate the mode of packing of [Pt(NIA)₂] in those compounds. Photoluminescence studies show that the photoluminescence behaviors of those compounds also depended on the carboxylate ligands. 1-4, 6, and 7 show blue light emission with fluorescence emission wavelengths of 437-440 nm despite the different carboxylate ligands used. 5 and 8 show green emissions with maximum intensity peak positions of 522 nm. Compared with that of 5 and 8, the emission of 9 and 10 has the same red shifts with peak positions of 567 and 528 nm. The variable-temperature photoluminescence studies reveal that 8 and 10 show two different thermal quenching (TQ) zones in the range of 80-420 K, while the emission intensity of 9 shows negative thermal quenching at low temperatures of 80-220 K and TQ in the range of 220-420 K.

Achieving colour tuneable and white-light luminescence in a large family of dual-emission lanthanide coordination polymers

Expanding the family of lanthanide terpyridine coordination polymers has yielded eighteen new complexes with two different phases, Ln(TPC)₂(HCOO)(H₂O) (Ln-1) and Ln(TPC)(HCOO)₂ (Ln-2) (Ln = Sm-Lu, except Tm). Both structures are composed of lanthanide cations interconnected by 2,2':6',2''-terpyridine-4'-carboxylate ligands to yield one-dimensional chain topologies. However, the incorporation of an additional crystallographically unique decorative TPC ligand into Ln-1 gives rises to a distinct phase. The encapsulation of both metal- and ligand-based phosphors within single coordination polymers leads to dual-emission of the afforded materials. Furthermore, judicious lanthanide doping in heterometallic Ln-1 and Ln-2 allows for fine-tuning the photoluminescent colours over a wide range of gamut. Such a combination showcases the capability to fine-tune the emission colours from deep green, to red, and to blue. In addition, direct white-light emission upon UV excitation can be achieved in the Sm_xGd_1-x-1 system.

Shedding light on predicting and controlling emission chromaticity in multicomponent photoluminescent systems

Predictable colour tuning in multicomponent photoluminescent (PL) systems is achieved using mixtures of simultaneously emitting organic molecules. By mitigating the potential for energy transfer through the control of concentration, the resulting emission chromaticity of five dichromic PL systems is approximated as a linear combination of the emitting components and their corresponding brightness (χ i , ϕ i , and I ex,i ). Despite being limited to dilute solutions (10-6 M), colour tuning within these systems was controlled by (1) varying the composition of the components and (2) exploiting the differences in the components' excitation intensities at common wavelengths. Using this approach, white light emission (WLE) was realized using a pre-determined mixture of red, green, and blue emitting organic molecules. Based on these results, materials and devices with built-in or programmable emission colour can be achieved, including highly sought-after WLE.

Theoretical Modeling (Sparkle RM1 and PM7) and Crystal Structures of the Luminescent Dinuclear Sm(III) and Eu(III) Complexes of 6,6,7,7,8,8,8- Heptafluoro-2,2-dimethyl-3,5-octanedione and 2,3-Bis(2-pyridyl)pyrazine: Determination of Individual Spectroscopic Parameters for Two Unique Eu3+ Sites

Heteroleptic homo dinuclear complexes [Sm(fod)₃(μ-bpp)Sm(fod)₃] and [Eu(fod)₃(μ-bpp)Eu(fod)₃] and their diamagnetic analogue [Lu(fod)₃(μ-bpp)Lu(fod)₃] (fod is the anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod) and bpp is 2,3-bis(2-pyridyl)pyrazine) are synthesized and thoroughly characterized. The lanthanum gave a 1:1 adduct of La(fod)₃ and bpp with the molecular formula of [La(fod)₃bpp]. The ¹H NMR and ¹H-¹H COSY spectra of the complexes were used to assign the proton resonances. In the case of paramagnetic Sm³⁺ and Eu³⁺ complexes, the methine (of the fod moiety) and the bpp resonances are shifted in the opposite direction and the paramagnetic shifts are dipolar in nature, which decrease with increasing distance of the proton from the metal ion. The single-crystal X-ray analyses reveal that the complexes (Sm³⁺ and Eu³⁺) are dinuclear and crystallize in the triclinic P1 space group. Each metal in a given complex is eight coordinate by coordinating with six oxygen atoms of three fod moieties and two nitrogen atoms of the bpp. Of the two metal centers, in a given complex, one has a distorted square antiprism arrangement and the other acquires a distorted dodecahedron geometry. The Sparkle RM1 and PM7 optimized structures of the complexes are also presented and compared with the crystal structure. Theoretically observed bond distances are in excellent agreement with the experimental values, and the RMS deviations for the optimized structures are 2.878, 2.217, 2.564, and 2.675 Å. The photophysical properties of Sm³⁺ and Eu³⁺ complexes are investigated in different solvents, solid, and PMMA-doped thin hybrid films. The spectroscopic parameters (the Judd-Ofelt intensity parameters, radiative parameters, and intrinsic quantum yield) of each Eu³⁺ sites are calculated using the overlap polyhedra method. The theoretically obtained parameters are close to the experimental results. The lifetime of the excited state is 38.74 μs for Sm³⁺ and 713.62 μs for the Eu³⁺ complex in the solid state.

Multimetal lanthanide phosphonocarboxylate frameworks: structures, colour tuning and near-infrared emission

A series of isostructural lanthanide phosphonocarboxylate frameworks {(H3O)3[Ln7(pbpdc)6(DMF)4(H2O)3]·4H2O}n (named LnPCF, Ln = Tb, Eu and Gd, H4pbpdc = 4'-phosphono-[1,1'-biphenyl]-3,5-dicarboxylic acid) were solvothermally synthesized and characterized by the single crystal X-ray diffraction technique. By combining lanthanide cations with a phosphonocarboxylate ligand, a heptametallic lanthanide phosphonate [Ln7(PO3)6(COO)12] core was obtained. This core exhibited as a rare highly 18-connected node and was linked by the 3-connected pbpdc4- ligand, forming a (3,18)-connected framework with a novel topology of {43}6{438·676·839}. This LnPCF structure is an ideal platform for accommodating various lanthanide ions. The TbPCF and EuPCF show efficient luminescence emission due to the "antenna effect" and incorporating Gd3+ into the TbPCF results in a drastic luminescence enhancement. Fine colour tuning between green and red can be easily achieved in bimetallic TbxGd1-xPCFs. More significantly, upon combining a few percent of Nd3+ and Gd3+ with Tb3+, the resulting trimetallic Tb0.4Gd0.5Nd0.1PCF shows dual emissions of both visible and near-infrared light.

Tuning of the Network Dimensionality and Photoluminescent Properties in Homo- and Heteroleptic Lanthanide Coordination Polymers

Targeted synthesis, through a heteroleptic methodology, has resulted in three types of lanthanide (Ln) coordination polymers (CPs) with tailored dimensionality, tunable photoluminescent colors, and distinct luminescence quenching upon UV and X-ray irradiation. The homoleptic Ln(tpbz)(NO₃)₂ [CP-1; tpbz = 4-(2,2':6',2″-terpyridin-4'-yl)benzoate] is assembled from Ln cations and bridging tpbz ligands, accompanied by the decoration of NO₃^- anions, forming a one-dimensional (1D) chain structure. The presence of ancillary dicarboxylate linkers, 1,4-benzenedicarboxylate (bdc) and 2,5-thiophenedicarboxylate (tdc), promotes additional bridging between 1D chains to form a two-dimensional layer and a three-dimensional framework for Ln(tpbz)(bdc) (CP-2) and Ln(tpbz)(tdc) (CP-3), respectively. The multicolor and luminescence properties of the obtained CPs were investigated, displaying typical red Eu^III-based and green Tb^III-based emissions. The Sm^III-bearing CP-1-CP-3, however, exhibit diverse ratiometric Ln^III- and ligand-based emissions, with the photoluminescent colors varying from pink to orange to cyan. Notably, the Tb^III-containing CP-1-CP-3 display distinct luminescence quenching upon continuous exposure to UV and X-ray irradiation. To our best knowledge, CP-2-Tb represents one of the most sensitive UV dosage probes (3.2 × 10^-7 J) among all CPs.

A new family of dinuclear lanthanide complexes exhibiting luminescence, magnetic entropy changes and single molecule magnet behaviors

Four isomorphic and dinuclear lanthanide complexes were synthesized. Complexes Eu^III and Tb^III exhibit strong emissions, while Gd^III shows the magnetocaloric effect and Dy^III displays a single-molecule magnet.

Synthesis and photoluminescence of three bismuth(III)-organic compounds bearing heterocyclic N-donor ligands

Three bismuth(iii)-organic compounds, [Bi4Cl8(PDC)2(phen)4]·2MeCN (1), [BiCl3(phen)2] (2), and [Bi2Cl6(terpy)2] (3), were prepared from solvothermal reactions of bismuth chloride, 2,6-pyridinedicarboxylic acid (H2PDC), and 1,10-phenanthroline (phen) or 2,2';6',2''-terpyridine (terpy). The structures were determined through single crystal X-ray diffraction and the compounds were further characterized via powder X-ray diffraction, Raman and infrared spectroscopy, and thermogravimetric analysis. The photoluminescence properties of the solid-state materials were assessed using steady state and time-dependent techniques to obtain excitation and emission profiles as well as lifetimes. The compounds exhibit visible emission ranging from the yellow-green to orange region upon UV excitation. Theoretical quantum mechanical calculations aimed at elucidating the observed emissive behavior show that the transitions can be assigned as predominantly ligand-to-ligand and ligand-to-metal charge transfer transitions. The solid-state structural chemistry, spectroscopic properties, and luminescence behavior of the bismuth compounds are presented herein.

Luminescent EuIIIand TbIIIbimetallic complexes of N,N′-heterocyclic bases and tolfenamic acid: structures, photophysical aspects and biological activity

The isostructural bimetallic luminescent Eu^IIIand Tb^IIIdimers containing N,N′-heterocyclic bases and tolfenamic acid as a bridging ligands were evaluated for their structures, cellular imaging capability and photocytotoxicity.