Terpyridyl-Imidazole Based Ligand Coordinated to Ln(Hexafluoroacetyl acetonate)3 Core: Synthesis, Structural Characterization, Luminescence Properties, and Thermosensing Behaviors in Solution and PMMA Film

A new array of ternary lanthanide complexes of the form [Ln(hfa)3(tpy-HImzphen)] have been synthesized and thoroughly characterized wherein Ln = LaIII (1), EuIII (2), SmIII (3), and TbIII (4); hfa = hexafluoroacetylacetonate; and tpy-HImzphen = 2-(4-[2,2':6',2″]terpyridin-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole. Incorporation of tpy-HImzphen onto the Ln-hfa moiety induced a bathochromic shift of the absorption window of the complexes into the visible region. Extensive investigations of the luminescence characteristics have been conducted both at RT and at 77 K to understand the deactivation pathways of the complexes. Both steady-state and time-resolved emission spectral behaviors indicate four distinctive behaviors upon incorporation of tpy-HImzphen onto the lanthanide core, viz., a huge red-shift of the ligand-centered peak for LaIII; almost complete energy transfer for EuIII; very little energy transfer for SmIII, while reverse energy transfer in the case of TbIII. In addition, the EuIII-complex exhibits its excellence in luminescence thermometry in the solution state as well as in poly(methyl methacrylate) (PMMA) thin films. The thermosensitive luminescence response in solution was further utilized to mimic set-reset flip-flop logic operation. A plausible energy transfer scheme has been devised to explain dissimilar luminescence behaviors in the complexes. The role of LMCT was also considered for the observed thermosensing property of the Eu(III) complex.

Heteroleptic samarium complexes with high quantum yields for temperature sensing applications

Two new crystallographically characterized samarium complexes, [Sm(fod)3(L1)] (1) and [Sm(fod)3(L2)] (2) {L1 = 4,7-diphenyl-1,10-phenanthroline (bath), L2 = 2,2':6',2''-terpyridine and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}, were synthesized and thoroughly characterized. Single-crystal (SC) analysis shows that complex 1 is an eight-coordinate structure with a distorted square antiprism geometry (D4d), whereas complex 2 possesses a nine-coordinate structure with distorted muffin geometry (Cs). The NMR results are in line with SC-XRD analysis, which further validate that the complexes remain intact in solutions. The photophysical characteristics of the complexes were studied in both visible and near infra-red (NIR) regions. The PLQY values of the present complexes were found to be higher than those reported in the literature except for a tetrakis Sm complex. This result indicates that both the ligands act as effective antennas for the present systems. A comparison of PLQY and emission lifetime values within the present complexes (in solid state) reveals that energy transfer from terpy to Sm3+ is more effective than that from the bath ligand. Various color parameters of the complexes were calculated, and the determined CCT values suggest that the complexes may be used as warm light sources. The determined band gap values for the complexes are in the range of those for semiconductors, which suggest the application of present systems in the field of optoelectronics. The curve between the emission intensity and temperature for complex 1 shows a perfect linearity (χ2 = 0.99), which suggests that this complex can have potential application as a temperature sensor in the range 60-350 K.

Tuning the Photometric Properties of Ternary Sm3+ Complexes Involving Mixed-Ligands

This research article deals with the synthesis of ternary Sm³⁺ complexes with 6,8-dichlorochromone-3-carboxaldehyde through solution-precipitation method. The photometric properties of resultant complexes were tuned by coordinating N-donor heterocyclic ligands with Sm³⁺ ion. The emission spectra, obtained in the visible region have been studied. Under optical excitation of 370 nm, the complexes displayed characteristic Sm³⁺-centered emission peaks at ~ 563, 600 and 647 nm in solution as well as in powder state. The complexes showed thermal stability up to 175 °C. The complexes delivered quantum yield as high as 7.91% and longest emission lifetime of 0.564 ms. The color coordinates of the complexes, located in deep orange (in solution) and red (in powder) spectral region, matched well with the Society of Motion Picture and Television Engineers and European Broadcasting Union. The properties of complexes have been investigated to a significant extent due to their easy synthesis and potential applications as orange-red light emitter in a wide range of photonic applications such as display devices, OLEDs, dashboards, optical systems.

Fluorinated β-diketone-based Sm(III) complexes: spectroscopic and optoelectronic characteristics

The synthesis and characterization of a series of octa-coordinated Sm(III) complexes with 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (TFNB) and 2,2'-bipyridine (Bpy) derivatives as ancillary ligand are described here. The complexes were analyzed by elemental, spectroscopic such as infrared spectroscopy, ¹ H NMR, and thermogravimetric analyses. The fluorinated TFNB ligand absorbs in the range from 200 to 400 nm. The complexes show the sharp and structured Sm-based emissions in visible region upon irradiation in UV range. Excitation spectra of complexes show similarity to the absorption spectra of ligands suggesting that excitation energy is transferred from ligands to Sm(III) centre by the antenna effect. Photoluminescence emission spectra and colour parameters affirmed that the complexes show luminescence in orange-red region. These luminous Sm(III) complexes might be applied as emissive layer in organic electroluminescent devices.

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.

Lanthanide nitrato complexes bridged by the bis-tridentate ligand 2,3,5,6-tetra(2-pyridyl)pyrazine: Syntheses, crystal structures, Hirshfeld surface analyses, luminescence properties, DFT calculations, and magnetic behavior

Six dinuclear lanthanide(III) nitrato complexes [Ln(NO₃)₃(H₂O)]₂(μ-tppz) (where tppz = 2,3,5,6-tetra(2-pyridyl) pyrazine and Ln(III) = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), and Dy (6)) with bis-tridentate N-heterocyclic 2,3,5,6-tetra(2-pyridyl)pyrazine as bridging ligand have been solvothermally synthesized and characterized via elemental analysis, infrared spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction, and powder X-ray diffraction. The 3-D Hirshfeld surface and 2-D fingerprint plots show that the main interactions in 1-6 are the O⋯H/H⋯O intermolecular interactions with relative contributions of about 62%. Although the poor lanthanide(III)-centered luminescence properties clearly point to the efficiency of nonradiative quenching processes (presence of water molecules in the coordination sphere of the lanthanide(III) ions), the ligand tppz is better suited to sensitize the lanthanide(III)'s emissions of Eu^III and Nd^III than Sm^III, Tb^III, and Dy^III. Finally, the magnetic data of Dy^III comple×6 reveals antiferromagnetic coupling between Dy^III ions.

Optical Properties of New Terbium(III) Ternary Complexes Containing Anionic 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and Neutral Sensitizers in Solution, Solid and PMMA Thin Films: Intra and Interphase Colour Tuning

Four new terbium(III) ternary complexes, [Tb(fod)₃ (indazole)] (1), [Tb(fod)₃ (tptz)] (2), [Tb(fod)₃ (impy)] (3) and [Tb(fod)₃ (tppo)₂ ] (4) with 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, (Hfod) and N and O donors are synthesized and structurally characterized. The photoluminescence of the complexes are studied in solid, chloroform solution and thin PMMA hybrid films (PMMA is a poly(methyl methacrylate)). The ligand-based emission is dominant in solution of 3 and 4. The effect of ancillary ligands on the photoluminescence of terbium(III) ion is investigated. The mechanism of energy transfer is discussed and correlates the luminescence of acceptor terbium ion with the triplet state energy level of donor ligands. Among the four complexes studied, the luminescence from 1 is most intense followed by 2, 4 and 3. The Commission International de I'Eclairage (CIE) color coordinates of these complexes are calculated and presented. The complexes 3 and 4 show intraphase color tuning when excited under different UV wavelengths. The emission color of [Tb(fod)₃ (tppo)₂ ] (4) changes from pure blue to turquoise green via almost pure white under 360, 328 and 280 nm UV excitation wavelengths respectively. The [Tb(fod)₃ (impy)] (3) show similar results. The complex [Tb(fod)₃ (tptz)] (2) displays interphase color tuning from yellow (solution) to turquoise green (solid) and fascinatingly incorporation of complex in PMMA polymer generates white light under same excitation wavelength (360 nm).

Two homochiral EuIII and SmIII enantiomeric pairs showing circularly polarized luminescence, photoluminescence and triboluminescence

Two homochiral EuIII and SmIII tris(β-diketonate) enantiomeric pairs, based on fluorinated β-diketone (Hbtfa) and enantiopure asymmetric N,N'-donor ligands (LR and LS), Λ-Eu(btfa)3LR (R-1-Eu)/Δ-Eu(btfa)3LS (S-1-Eu) and Λ-Sm(btfa)3LR (R-2-Sm)/Δ-Sm(btfa)3LS (S-2-Sm) (btfa- = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate and LR/LS = (-)/(+)-4,5-pineno-2,2'-bipyridine) were synthesized. The electronic circular dichroism (ECD) spectra confirmed their enantiomeric nature. R-1-Eu/S-1-Eu and R-2-Sm/S-2-Sm exhibit intense characteristic emissions of EuIII (red) and SmIII (orange-red) ions both in the solid state and in DCM with long lifetimes and high luminescence quantum yields. For example, the overall quantum yields reach up to 61% and 53% along with very high sensitization efficiency values of 82 and 79 for R-1-Eu in the solid state and in DCM, respectively. Notably, the corresponding values are determined to be 6.5% (solid state) and 3.1% (DCM) for R-2-Sm, which are among the highest quantum yields for rare SmIII tris(β-diketonate) luminescent complexes reported to date. Furthermore, R-1-Eu and R-2-Sm show a strong triboluminescence (TL) phenomenon visible with the naked eye in daylight. Moreover, R-1-Eu/S-1-Eu and R-2-Sm/S-2-Sm show circularly polarized luminescence (CPL) properties. Particularly, the luminescence dissymmetry factors (glum) for R-2-Sm/S-2-Sm are larger than those for R-1-Eu/S-1-Eu despite the fact that SmIII complexes usually show poorer emission than EuIII homologues, which is very rare in the reported EuIII and SmIII CPL-active complexes.

Seven-coordinate LnIII complexes assembled from a bulky MesacacH ligand: their synthesis, structure, photoluminescence and SMM behaviour

The reaction of a bulky acetyl acetone ligand 1,3-dimesitylpropane-1,3-dione (MesacacH) with hydrated lanthanide chlorides in the presence of tetramethylammonium hydroxide afforded a new family of neutral mononuclear LnIII complexes [Ln(Mesacac)3(DMF)] (Ln = Dy (1); Tb (2); Y0.91Dy0.09 (3); and Er (4)). The molecular structures of these complexes were confirmed by single crystal X-ray diffraction studies. The coordination geometries of the LnIII centre were analysed by SHAPE analysis which revealed a capped octahedral geometry in 1-4. Photoluminescence studies showed ligand-sensitized green emissions for 2 with an appreciable quantum yield of 0.83%. Static (dc) and dynamic (ac) magnetic studies of complexes 1 and 3 were performed. The dynamic magnetic study revealed that complex 1 exhibits zero-field slow relaxation of the magnetization without showing a clear maximum in the out-of-phase ac susceptibility plots. However, magnetic dilution of 1 with the YIII metal ion (complex 3) and/or the application of a dc magnetic field induces a strong frequency dependence of the ac susceptibility signals with χ''M peaks in the 3-10 K temperature range, thus supporting field-induced SMM behaviour of 1. The relaxation process takes place through a combination of the Orbach and Raman mechanisms. The fitting of the temperature dependence of the relaxation time to the equation τ-1 = τ0-1 exp(-Ueff/kBT) + BTn, allows the extraction of the effective energy barrier Ueff/kB = 70 K (48.7 cm-1) and pre-exponential parameter of τ0 = 2.7 × 10-7 s for the Orbach mechanism (first term) and the parameters B = 0.04 s-1 K-n and n = 6.11, for the Raman mechanism (second term).

Effect of ancillary ligands on visible and NIR luminescence of Sm3+β-diketonate complexes

Two new Sm³⁺ complexes with pyrazolic β-diketones bearing a CF₃ group acting as main ligands and with 2,2'-bipyridine or 1,10-phenanthroline being the ancillary ligand were studied, and their energy level structure was established. Stark splitting observed in the photoluminescence spectra of the complexes points to their non-cubic symmetry, confirmed by the calculated Judd-Ofelt intensity parameters. Internal quantum yields obtained for the compounds by the Judd-Ofelt calculations were of the order of 5.5%, whereas the measured external quantum yields were 0.75% and 1.5% for Sm³⁺ complexes involving 2,2'-bipyridine and 1,10-phenanthroline ancillary ligands, respectively, with the corresponding sensitization efficiencies calculated as 0.16 and 0.26. It was demonstrated that replacing the 1,10-phenanthroline ancillary ligand with 2,2'-bipyridine provides an increase in the intensity of 650 nm emission of the Sm³⁺ complexes, with the branching ratio reaching 55%. Intensive emission of the studied complexes at 650 nm offers hope for their use as spectrally pure red emitters.

A conjugated porphyrin as a red-light sensitizer for near-infrared emission of ytterbium(iii) ion

A conjugated porphyrin with broader absorption in the visible region was synthesized for sensitizing the near-infrared emission of ytterbium(iii) ions.

Luminescent europium(iii) and terbium(iii) complexes of β-diketonate and substituted terpyridine ligands: synthesis, crystal structures and elucidation of energy transfer pathways

A series of coordinatively saturated Ln^III complexes: [Ln(R-TPY)(TTA)₃] (1–6) were designed and structurally characterized and plausible energy transfer (ET) pathways determined using a theoretical method.

Syntheses and crystal structures of new dinuclear lanthanide complexes based on 3-(4-hydroxyphenyl)propanoic acid: Hirshfeld surface analyses and photoluminescence sensing

A series of ten new lanthanide complexes, [Ln₂(HPA)₆(bipy)₂·4H₂O·2bipy], were synthesized and their photoluminescence sensing and Hirshfeld surface analyses performed.