Ytterbium 10-carboxyperylene-3,4,9-tricarboxylates for targeted NIR luminescent bioimaging.

Two new ytterbium coordination compounds Yb(HPTC)(H2O)2 (Yb1) and Yb(HPTC)(Phen) (Yb2) were obtained using 10-carboxyperylene-3,4,9-tricarboxylate ion (HPTC3-) as a sensitizer. Both coordination compounds exhibited intense NIR-II luminescence upon excitation in the visible range and formed stable suspensions with nanoparticles of 50-70 nm in size in an aqueous solution of sodium alginate. Both complexes demonstrated non-toxicity up to at least 25 mg L-1 in two cell cultures: cancer cells MCF7 and embryonic cells HEK293T - making them suitable for bioimaging. For both complexes, the accumulation in cells was directly measured and it was shown that the accumulation of Yb2 was the same for both cell types (0.51-0.52 πg per cell), while Yb1 demonstrated selective accumulation in cancer cells (0.04 πg per cell for HEK293T and 7.00 πg per cell for MCF7). Thus, Yb1 can also be proposed as a selective vis-excited NIR emitting bioprobe.

The increase of europium-based OLED luminance through reducing the excited state lifetime by mixed-ligand complex formation.

An approach to the luminance increase of the europium-based OLED is proposed through the formation of the mixed-ligand complex. The introduction of two diverse anionic ligands around one europium ion forming a mixed-ligand complex is confirmed by powder X-ray diffraction, 1H and 19F NMR spectroscopy, MALDI MS spectroscopy, and luminescence spectroscopy. A decrease in the symmetry of the coordination environment leads to a 50% reduction of the lifetime of the excited state. The obtained OLEDs based on mixed ligand europium complexes are significantly superior in luminance to OLEDs based on individual complexes.

Solution-Processed OLED Based on a Mixed-Ligand Europium Complex.

An approach to increase the efficiency of europium-based OLEDs was proposed through the formation of a mixed-ligand complex. The design of a series of europium complexes, together with an optimization of the solution deposition, including the host selection, as well as the variation of the solvent and deposition parameters, resulted in a noticeable increase in OLED luminance. As a result, the maximum luminance of the Eu-based OLED reached up to 700 cd/m2, which is one of the highest values for an Eu-based solution-processed OLED. Finally, its stability was investigated.

A 50% increase in the terbium-based OLED luminance through reducing the excited-state lifetime due to the introduction of gold nanoparticles.

An increase in the efficiency for a terbium-based OLED was achieved by introducing gold nanoparticles into the PEDOT:PSS hole injection layer and was mainly due to the improvement in carrier injection and the reduction of the excited-state lifetime. The introduction of plasmon-resonant gold nanoparticles resulted in a 50% increase in the Tb(czb)3TDZP luminance, which reached 480 cd m-2 and is the highest result for OLEDs based on aromatic carboxylates.

NIR luminescence thermometers based on Yb-Nd coordination compounds for the 83-393 K temperature range.

Multimetallic neodymium-ytterbium-gadolinium compounds with 9-anthracenate and 9-acridinate anions were tested in order to create the first luminescent thermometer for elevated temperatures. High luminescence intensity and high signal resolution were reached thanks to the concentration quenching elimination due to the partial substitution of the emitting ions with Gd3+. As a result, NIR emitting materials for luminescence thermometry in the wide temperature range (83-393 K) based on lanthanide coordination compounds (CCs) were obtained. The best thermometric properties among the studied systems were demonstrated by Yb0.02Nd0.12Gd0.86(ant)3, and its temperature sensitivity reached 1.8% K-1 in the temperature range of 293-393 K.

Record efficiency of 1000 nm electroluminescence from a solution-processable host-free OLED.

New ytterbium complexes K(Solv)x[Yb(Ln)2] (Solv = ethanol and/or water) with 2-tosylaminobenzylidene-aryloylhydrazones (H2L1, aryloyl = benzoyl; H2L2, aryloyl = 2-naphthoyl) demonstrated high solubility and hole mobility (ca. 2.6 × 10-6 cm2 V-1 s-1), while their electron mobility and PLQY were different. The substitution of a benzoyl substituent with naphthoyl resulted in a significant increase of the electron mobility (6.9 × 10-7vs. 1.7 × 10-6 cm2 V-1 s-1) and a decrease of the quantum yield (1.2% vs. 0.6%). As a result, the optimized OLEDs based on the K[Yb(Ln)2] layer demonstrated efficiencies up to 385 µW W-1 and 441 µW W-1, indicating the superior importance of charge mobility over the quantum yield. These are the highest efficiencies of the Yb electroluminescence.

Europium complexes with dinitropyrazole: unusual luminescence thermal behavior and irreversible temperature sensing.

Europium 3,5-dinitropyrazole complexes demonstrate an unusual luminescence behavior upon heating, i.e. there is a noticeable increase of the luminescence intensity beyond a temperature of 200 °C. We propose and successfully demonstrate the possibility of using this phenomenon for sensing overheating above this temperature. An on/off ratio of 37 is reached.

Identifying lifetime as one of the key parameters responsible for the low brightness of lanthanide-based OLEDs.

OLEDs based on lanthanide complexes have decisive optical advantages but are hampered by low brightness. Despite the efforts to optimize several parameters such as quantum yield and charge carrier mobility, there seems to be another key parameter that hinders their performances. Experimental data are therefore collected for mixed-ligand europium complexes with bathophenanthroline and different classes of anionic ligands and screened to identify the key parameter responsible for this situation, which turns out to be the long lifetime of their excited states. A broad literature search supports this conclusion, showing that lanthanide complexes are inferior to other classes of OLED emitters often because of their long lifetimes; furthermore, among a series of lanthanide complexes, the best results are achieved for those with the shortest lifetimes, even though they suffer from low quantum yields.

Eu(tta)3DPPZ-based organic light-emitting diodes: spin-coating vs. vacuum-deposition.

The effect of the emission layer deposition method on the characteristics of OLEDs was studied on the example of the europium mixed-ligand complex Eu(tta)3DPPZ (tta: 2-thenoyltrifluoroacetone, DPPZ: dipyrido[3,2-a:2'c,3'c-c]phenazine). The maximum brightnesses of both OLEDs almost coincided, though OLED based on the spin-coated layer operated at lower voltages. The reason for that was the higher density and smoothness of the solution-processed layer.

Dual vis-NIR emissive bimetallic naphthoates of Eu-Yb-Gd: a new approach toward Yb luminescence intensity increase through Eu → Yb energy transfer.

Homo- and heteroligand mono-, bi-, and trimetallic lanthanide naphtoates EuxYbyGd1-x-y(naph)3(Phen)n (n = 0, 1) were obtained and thoroughly investigated. Homoligand naphthoates of the new phase were obtained as anhydrous powders from water. The photophysical properties of the obtained compounds were studied in detail. The first example of Eu-to-Yb energy transfer was found in these systems. Careful selection of the metal ratio allowed a dual vis-NIR emissive complex with a ytterbium quantum yield of 1.5% to be obtained.

Highly NIR-emitting ytterbium complexes containing 2-(tosylaminobenzylidene)-N-benzoylhydrazone anions: structure in solution and use for bioimaging.

Solution behaviour in DMSO using 1D and 2D NMR spectroscopy was performed for lanthanide complexes Ln(L)(HL) and Ln(HL)2Cl, containing non-macrocyclic 2-(tosylamino)-benzylidene-N-benzoylhydrazone (H2L), and the structure of [Yb(L)]+ cation in solution was determined. Based on the NMR data, the possibility to obtain novel complexes containing [Ln(L)2]- was predicted, which was successfully synthesized, and the crystal structure of K(C2H5OH)3[Yb(L)2] was determined. Thanks to its high quantum yield of NIR luminescence (1.3 ± 0.2%), high absorption, low toxicity, and the stability of its anion against dissociation in DMSO, K(H2O)3[Yb(L)2] was successfully used for bioimaging.

Various Structural Design Modifications: para-Substituted Diphenylphosphinopyridine Bridged Cu(I) Complexes in Organic Light-Emitting Diodes.

The well-known system of dinuclear Cu(I) complexes bridged by 2-(diphenylphosphino)pyridine (PyrPhos) derivatives Cu2X2L3 and Cu2X2LP2 (L = bridging ligand, P = ancillary ligand) goes along with endless variation options for tunability. In this work, the influence of substituents and modifications on the phosphine moiety of the NP-bridging ligand was investigated. In previous studies, the location of the lowest unoccupied molecular orbital (LUMO) of the copper complexes of the PyrPhos family was found to be located on the NP-bridging ligand and enabled color tuning in the whole visible spectrum. A multitude of dinuclear Cu(I) complexes based on the triple methylated 2-(bis(4-methylphenyl)phosphino)-4-methylpyridine (Cu-1b-H, Cu-1b-MeO, and Cu-1b-F) up to complexes bearing 2-(bis(4-fluorophenyl)phosphino)pyridine (Cu-6a-H) with electron-withdrawing fluorine atoms over many other variations on the NP-bridging ligands were synthesized. Almost all copper complexes were confirmed via single crystal X-ray diffraction analysis. Besides theoretical TDDFT-studies of the electronic properties and photophysical measurements, the majority of the phosphino-modified Cu(I) complexes was tested in solution-processed organic light-emitting diodes (OLEDs) with different heterostructure variations. The best results of the OLED devices were obtained with copper emitter Cu-1b-H in a stack architecture of ITO/PEDOT-PSS (50 nm)/poly-TPD (15 nm)/20 wt % Cu(I) emitter:CBP:TcTA(7:3) (45 nm)/TPBi (30 nm)/LiF(1 nm)/Al (>100 nm) with a high brightness of 5900 Cd/m2 and a good current efficiency of 3.79 Cd/A.

New approach to increase the sensitivity of Tb-Eu-based luminescent thermometer.

The formation of trimetallic terbium-europium-gadolinium complexes was proposed as an approach to increase the sensitivity of the corresponding terbium-europium complexes for temperature measurement due to the suppression of multiphotonic emission. This approach results in over a 2-fold increase of the sensitivity of Eu-Tb carboxylate, which reached 5.3% K-1 in the physiological range.

On the development of a new approach to the design of lanthanide-based materials for solution-processed OLEDs.

The targeted design of lanthanide-based emitters for solution-processed organic light-emitting diodes (OLEDs) resulted in obtaining an NIR OLED with one of the highest efficiencies among ytterbium-based solution-processed OLEDs (30 µW W-1). The design was aimed at the combination of high luminescence efficiency with solubility and charge carrier mobility. The latter was achieved thanks to the introduction of the purposefully selected neutral ligands, which combine electron mobility and the ability to sensitize lanthanide luminescence. Besides, the HOMO and LUMO energies and charge carrier mobility of solution-processed thin films of coordination compounds were measured experimentally for the first time, and novel highly luminescent europium-based materials with PLQYs of up to 80% and purely NIR luminescent ytterbium complexes were obtained.

TbO+ in a calcium apatite matrix featuring a triple trigger-type relaxation of magnetization.

Tb for Ca substituted hydroxyapatite ceramic samples with composition Ca10-xTbx(PO4)6(OH1-x/2-δ)2, where x = 0.1, 0.5, were synthesized by solid-state reaction at 1300 °C in air, and their crystal structure, vibrational spectra, luminescence, and magnetic properties were studied. Implanting Tb3+ into the calcium apatite crystal lattice results in formation of an effective TbO+ ion which displays a short terbium-oxygen bond of 2.15 Å and a stretching vibration at 534 cm-1. The Tb3+ electronic structure has been revealed by analyzing the luminescence spectra and dc/ac magnetization data. Accordingly, the ground state represents a pseudo doublet with MJ = ±6 and the first exited level is by 112 cm-1 higher in energy. The ion exhibits field induced magnetic bistability with the magnetization reversing over the first exited state. Three paths of magnetization relaxation with field-temperature controlled switching between the paths have been identified.

The development of a new approach toward lanthanide-based OLED fabrication: new host materials for Tb-based emitters.

To develop the recently proposed approach toward host selection for lanthanide-based emitters, four phosphine oxides PO = PO1-PO4 were investigated which are able to both increase the electron mobility and to sensitize terbium luminescence. New highly soluble and brightly luminescent terbium complexes TbCl3(PO)·H2O and Tb(pobz)3(PO)·(CH3)2CO (pobz- = phenoxybenzoate) with a quantum yield of up to 100% were synthesized and thoroughly characterized. To study the electroluminescence properties of these materials, a series of solution-processed OLED devices were fabricated and their heterostructures were selected based on the HOMO and LUMO energies of PO1-PO4, which were carefully assessed by the combination of DFT and TDDFT methods. Thus, the effectiveness of the proposed approach was proved, and the influence of the anionic ligand was shown. The maximum OLED luminance reached 75 Cd m-2, which is a high value for solution-processed OLEDs based on terbium complexes.

Remarkable high efficiency of red emitters using Eu(iii) ternary complexes.

We have synthesized Eu(iii) ternary complexes possessing record photoluminescence yields up to 90%. This high luminescence performance resulted from the absence of quenching moieties in the Eu coordination environment and an efficient energy transfer between ligands, combined with a particular symmetry of the coordination environment.

The peculiarities of complex formation and energy transfer processes in lanthanide complexes with 2-(tosylamino)-benzylidene-N-benzoylhydrazone.

Depending on the local excess of lanthanide ions (Ln = Lu, Yb, Er, Dy, Tb, Gd, Eu, Nd) or 2-(tosylamino)-benzylidene-N-benzoylhydrazone (H2L), lanthanide complexes, containing either a mono-deprotonated ligand (Ln(HL)2X, X = Cl, NO3) or both mono- and dideprotonated ligands (Ln(L)(HL)), were preparatively obtained. The crystal structures of Lu(HL)2Cl, Yb(L)(HL)(H2O)2, Yb(L)(HL)(EtOH)2(H2O) and Er(L)(HL), determined by single crystal diffraction data or from powder diffraction data using Rietveld refinement, have shown the surprising resemblance. The study of luminescence temperature dependence of Eu(HL)2Cl and Eu(L)(HL) showed that europium luminescence is quenched by thermally-activated 5D0 → T1 energy transfer. Luminescent thermometers based on these complexes demonstrated the sensitivity of up to 7.7% at 85 K which is the highest value above liquid-nitrogen temperatures obtained to date.

From Isolated Anions to Polymer Structures through Linking with I2: Synthesis, Structure, and Properties of Two Complex Bismuth(III) Iodine Iodides.

We report the synthesis, crystal structures, and optical properties of two new compounds, K18Bi8I42(I2)0.5·14H2O (1) and (NH4)7Bi3I16(I2)0.5·4.5H2O (2), as well as the electronic structure of the latter. They crystallize in tetragonal space group P4/ mmm with the unit cell parameters a = 12.974(1) and c = 20.821(3) Å for 1 and a = 13.061(3) and c = 15.162(7) Å for 2. Though 1 and 2 are not isomorphous, their crystal structures display the same structural organization; namely, the BiI6 octahedra are linked by I2 units to form disordered layers in 1 and perfectly ordered chains in 2. The I-I bond distances in the thus formed I-I-I-I linear links are not uniform; the central bond is only slightly longer than in a standalone I2 molecule, whereas the peripheral bonds are significantly shorter than longer bonds typical for various polyiodides, which is confirmed by Raman spectroscopy. The analysis of the electronic structure shows that the atoms forming the I-I-I-I subunits transfer electron density from their occupied 5p orbitals onto their vacant states as well as onto 6s orbitals of bismuth atoms that center the BiI6 octahedra. This leads to low direct band gaps that were found to be 1.57 and 1.27 eV for 1 and 2, respectively, by optical absorption spectroscopy. Luminescent radiative relaxation was observed in the near-IR region with emission maxima of 1.39 and 1.24 eV for 1 and 2, respectively, in good agreement with the band structure, despite the strong quenching propensity of I2 moieties.

"Isolated" DyO+ Embedded in a Ceramic Apatite Matrix Featuring Single-Molecule Magnet Behavior with a High Energy Barrier for Magnetization Relaxation.

Meeting the challenges of Moore's Law, predicting ambitious miniaturization rates of integrated circuits, requires to go beyond the traditional top-down approaches, and to employ synthetic chemistry methods, to use bottom-up techniques. During the recent decades, it has been shown that open-shell coordination compounds may exhibit intramolecular spontaneous magnetization, thus offering promising prospects for storage and processing of digital information. Against this background we regarded it rewarding to implement similar magnetic centers into a ceramic material, which would provide better long-term mechanical and chemical durability. Here we present new robust inorganic compounds containing separate DyO+ ions in an apatite matrix, which behave like single-molecule magnets. The materials exhibit a blocking temperature of 11 K and an energy barrier for spin reversal of a thousand inverse centimeters which is among the highest values ever achieved.