Lanthanide complexes with 2-(tosylamino)-benzylidene-N-(aryloyl

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Lanthanide complexes with 2-(tosylamino)-benzylideneN-(aryloyl)hydrazones - universal luminescent materials Anton Kovalenko, Pavel O. Rublev, Lyubov O Tcelykh, Alexander S. Goloveshkin, Leonid S. Lepnev, Anatolii S. Burlov, Andrey A Vashchenko, Lukasz Marciniak, Abel M. Magerramov, Namig G. Shikhaliyev, Sergey Z. Vatsadze, and Valentina V. Utochnikova Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b03675 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 4, 2019

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Chemistry of Materials

Lanthanide complexes with 2-(tosylamino)-benzylidene-N(aryloyl)hydrazones - universal luminescent materials Anton Kovalenko†,√, Pavel O. Rublev†, Lyubov O. Tcelykh†, Alexander S. Goloveshkin‡, Leonid S. Lepnev∆, Anatolii S. Burlov§, Andrey A. Vashchenko∆, Łukasz Marciniak∑, Abel M. Magerramov∞, Namig G. Shikhaliyev∞, Sergey Z. Vatsadze† and Valentina V. Utochnikova*,†,‰ †

Faculty of Chemistry, Lomonosov Moscow State University, Russia, 119991, Moscow 1, GSP-1, 1-3 Leninskiye Gory

√ Centre de Biophysique Moléculaire - UPR 4301, Center National De La Recherche Scientifique, France, 45071 Orléans, Rue Charles Sadron ‡

A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Russia, 119991, GSP-1, Moscow, Vavilova St. 28 ∆ Lebedev Physical Institute, Russian Academy of Sciences, Russia, 119991, GSP-1, Moscow, Leninsky Avenue 53 §

Institute of Physical & Organic Chemistry, Southern Federal University, Russia, 344090, Rostov-on-Don, Stachka Ave., 194/2 ∑ Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P Nr 1410, 50-950 Wrocław 2, Poland ∞ ‰

Faculty of Chemistry, Baku State University, Azerbaijan, Baku, AZ 1148, Academic Zahid Xalilov street, 23 SIA Evoled, Latvia,LV-1050, Riga, 1a-24 Puskina iela

ABSTRACT: Lanthanide complexes Ln(L1)(HL1) (Ln = Lu, Yb, Er, Gd, Eu, Sm) and Ln(L2)(HL2) (Ln = Lu, Yb, Gd, Eu) with 2(tosylamino)-benzylidene-N-(aryloyl)hydrazones (H2L1, aryloyl = 2-hydroxybenzoyl; H2L2, aryloyl = Isonicotinoyl) were obtained with the aim to explore them as new luminescent materials. They were found to form monomeric species independently on the aryloyl nature, their crystal structures were determined from single crystal X-ray data (Yb(L2)(HL2)·0.5(C2H5OH)), as well as from powder X-ray data by Rietveld refinement (Eu(L1)(HL1)). Ytterbium complexes exhibited intense luminescence, which allowed using them in host-free OLEDs, which demonstrated remarkable efficiency of NIR electroluminescence (50 µW/W) at low voltage (5V). Special mechanism of europium luminescence quenching allowed using europium complexes as luminescent thermometers, which demonstrated very high sensitivity up to 12%/K. The theory of luminescence thermometry based on three-level system was proposed which allowed predicting sensitivity with high accuracy (error within 20%).

INTRODUCTION Due to the filling of 4f electron shell, lanthanide ions posses unique optical properties, such as line-like emission bands, constant position of luminescence bands and long values of luminescence lifetimes, that makes lanthanide compounds irreplaceable luminescence materials1–8. At the same time, according to Laporte rule, f–f transitions are forbidden, and lanthanide ions posses low absorption coefficients, which makes photoexcitation of Ln3+ low-efficient9,10. To overcome this problem, different organic chromophores are used as “antennas“, which are able to absorb the energy of excitation light and sensitize the lanthanide ions11–13. Additionally to the increase of molar absorption coefficient, formation of coordination compounds gives an excellent possibility to design luminescence materials for application in bioimaging9,14–19, luminescence thermometry20–25, organic light emitting diodes26–37, answering specific demands38–40. Different classes of anionic and neutral ligands have been studied so far, among which beta-diketonates41–46 and acylpyrazolates47–49 excel because of their high volatility, aromatic carboxylates stand out due to high thermal and optical stability, and complexes with macrocyclic ligands are well-recognized for their excellent stability against

dissociation. Lanthanide complexes with Schiff bases are also in the scope of interest50–55, as their high stability and infinite design possibility allows obtaining brightly luminescent materials based on them for various applications. Nevertheless, they are much less investigated by now, and their potential is still hidden. In our previous works53,54 we started investigating lanthanide complexes with N,N,O,O-donor ligand 2(tosylamino)-benzylidene-N-benzoylhydrazone (H2L, R = Ph in Figure 1), which have already demonstrated excellent luminescent properties in the NIR range54, as well as proven themselves as highly sensitive luminescent thermometers53. In the present paper we keep investigating this class of materials in order to further improve their performance. So, two new ligands H2L with different substituents -R (Figure 1) were synthesized, and their lanthanide complexes were obtained and investigated: europium complexes were used for luminescent thermometry, while ytterbium complexes were studied as materials for NIR emitting organic light-emitting diodes (OLEDs).

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R1 = O

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H2Ln Figure 1. Structural formula of the ligands. H2L1: R1 = (2hydroxyphenyl), H2L2: R2 = (4-Pyridyl). H2L: R = Ph 53,54

RESULTS AND DISCUSSION Synthesis, characterization and structure of lanthanide complexes Complexes of the composition Ln(L1)(HL1) (Ln = Lu, Yb, Er, Gd, Eu, Sm) and Ln(L2)(HL2) (Ln = Lu, Yb, Gd, Eu) were obtained by the reaction between the freshly-prepared lanthanide hydroxide and the ligand in ethanol (H2L1) or ethanol-acetonitrile solution (H2L2). Ln(OH)3 + 2H2Ln = Ln(Ln)(HLn) + 2H2O The solubility of Ln(L1)(HL1) and Ln(L2)(HL2) was quite different: while the сomplexes Ln(L1)(HL1) were almost insoluble in common organic solvents, the complexes of composition Ln(L2)(HL2) possessed high solubility in ethanol and acetonitrile. Thus, Ln(L1)(HL1) precipitated during the reaction, while Ln(L2)(HL2) complexes were formed in solution. Therefore, to avoid the impurity of the initial compounds, the Ln(L1)(HL1) complexes were synthesized in the excess of the ligand in solution, while Ln(L2)(HL2) were synthesized in the excess of the insoluble lanthanide hydroxide. The single crystal of Yb(L2)(HL2)·0.5(C2H5OH) was obtained by the crystallization from ethanol, and its crystal structure was determined by single crystal X-ray diffraction experiments. It consists of the monomeric species [Yb(L2)(HL2)] (Figure 2a), in which the fragments of benzylidene-N-benzoylhydrazone were almost orthogonal to each other, and the coordination environment of the lanthanide ion (4O+4N) consisted of two oxygen and two nitrogen atoms from each of the two ligand anions. The monomeric species [Yb(L2)(HL2)] in crystal are linked by N···H–O and N···H-N hydrogen bonds and π-stacking interaction between aromatic rings (Figure 2b). Very similar structures were observed by us previously for lanthanide complexes [Ln(HxL)(HL)]Clx∙solv (x = 0, 1; solv = H2O, EtOH; H2L = 2-(tosylamino)-benzylideneN-benzoylhydrazone, Figure 1, R = Ph) 53. The solvent molecules and inorganic anions, even if present, were not coordinated by the lanthanide ion and did not influence the structure of the monomeric species [Ln(HxL)(HL)]x+ (x = 0, 1). At the same time, the packing of the monomeric fragments were different that resulted in different XRD powder diffraction patterns.

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According to powder XRD (see ESI), powders of Ln(L2)(HL2) (Ln = Eu, Gd, Lu) are isostructural in the row, and their powder patterns correspond to the individual compounds indexable in P21/c, a = 14.87 Å, b = 13.24 Å, c = 20.20 Å, β = 104.1̊ (for Eu(L2)(HL2), Figure 3b). At the same time, the experimental diffraction patterns and lattice parameters of powders Ln(L2)(HL2) did not coincide with those calculated from singe crystal X-ray data for Yb(L2)(HL2)·0.5(C2H5OH), despite the obtained cell parameters are close to each other. This can be explained by the presence of ethanol molecule in the single crystal and the absence of solvent molecules in powder that results in the different packing of monomeric species and different powder diffraction patterns. However, we can expect the similar structure of monomeric species in single crystal and powder, and the same situation was observed by us in 53, namely, similar monomeric species structure but different packing mode. The X-ray diffraction patterns of powders of Ln(L1)(HL1) (Ln = Sm, Eu, Gd, Yb, Lu, see ESI) correspond to the individual isostructural compounds with the lattice parameters P-1, a = 10.85 Å, b = 11.39 Å, c = 17.08 Å, α = 84,6,β = 75.6̊, γ = 84.3 (for Eu(L1)(HL1), Figure 3a). The obtained cell parameters of Ln(L1)(HL1) were closest to the published structure of Lu(HL)2Cl53. That is why we decided to solve the structure of Ln(L1)(HL1) by Rietveld refinement using the structure of Lu(HL)2Cl as a starting model. The hydroxyl groups were added to the phenyl rings, and the chlorine anion was deleted, then the structure of Eu(L1)(HL1) was refined (Figure 2c, for details of structure refinement see Experimental section). The important task of the structure refinement was the determination of the –OH group coordination abilities. The answer is that the -OH group forms hydrogen bonds and is not coordinated by Eu3+ (Figure 2d). The coordination environment (4O+4N) of the lanthanide ion in Eu(L1)(HL1) is the same as in Yb(L2)(HL2)·0.5(C2H5OH) and previously published structures53, the complex consists of the mononuclear species [Eu(L1)(HL1)]. In the refined structure the hydroxyl group O4-H4 of the first ligand in [Eu(L1)(HL1)] forms intermolecular bond with carboxyl O7 atom of the other mononuclear species, therear NH-group N3-H3 forms intermolecular bond with O4. Hydroxyl group O8-H8 of the second ligand forms hydrogen bond with N6 atom. The hydrogen bonded centrosymmetric dimers in crystal are bonded via C-H···O, C-H···π and π···π interactions. Additionally to X-ray diffraction data, the composition of the complexes was confirmed by elemental analysis. The absence of the solvent molecules in complexes was determined from the IR spectra by the absence of the characteristic broad –OH bands. According to the thermal analysis data, Eu(L1)(HL1) is stable up to 320 ̊C, while Lu(L2)(HL2) is stable up to 390 ̊C. Such a difference in the thermal stability between Ln(L1)(HL1) and Ln(L2)(HL2) may be attributed to the presence of the –OH group in the structure of H2L1 that may decrease the thermal stability of the complexes.


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Figure 2 Crystal structures of the complexes. a) The general view of Yb(L2)(HL2)·0.5(C2H5OH) in crystal. Atoms are represented by thermal displacement ellipsoids (p=50%). Hydrogen atoms with the exception of NH proton omitted for clarity. b) Hydrogen bonds in Yb(L2)(HL2)·0.5(C2H5OH), only NH and OH hydrogen atoms are shown for clarity. c) The general view of Eu(L1)(HL1) in crystal. Atoms are represented by thermal displacement ellipsoids (p=50%). Hydrogen atoms with the exception of NH and OH groups omitted for clarity. d) Hydrogen bonds in Eu(L1)(HL1), only NH and OH hydrogen atoms are presented for clarity.


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Figure 3 Le Bail fit of PXRD patterns of a) Ln(L1)(HL1) (in the case of Ln = Eu), and b) Lu(L2)(HL2) (in the case of Ln = Eu).The experimental (blue line), calculated (red line) and their difference (grey curve).

Luminescence spectroscopy of the lutetium and gadolinium complexes Gd(III) and Ln(III) ions do not possess the ionic luminescence so the luminescence of these complexes corresponds to the luminescence of organic ligand, thus they can be used to determine the energy of the singlet and triplet exited states of the ligands. The photoluminescence spectra of the complexes Lu(L1)(HL1), Lu(L2)(HL2), Gd(L1)(HL1), Gd(L2)(HL2) are presented in Figure 4. Both Lu(L1)(HL1) and Lu(L2)(HL2) complexes demonstrate broadband luminescence with the maximum at 540 nm and 520 nm, correspondingly, which can be attributed to the fluorescence of L2– as well as HL– anions. The energies of the singlet states, roughly estimated from the luminescence spectra maxima, were equal to: S1((L1)2–) = 18500 cm–1 and S1((L2)2–) = 20400 cm–1. Gadolinium complexes can demonstrate phosphorescence56 due to the high magnetic moment of Gd3+ that allows determining the energy of triplet state levels. Indeed, both Gd(L1)(HL1) and Gd(L2)(HL2) represent broadband phosphorescence at 298 K as well as 77 K with observed

lifetime 20±2 µs and 6±2 µs, correspondingly (see ESI), and these phosphorescence bands can be observed in the luminescence spectra with 10 µs time delay, in which no fluorescence can be observed (see ESI, Figures 17, 18). The triplet energy levels can be calculated from the Gd(L1)(HL1) and Gd(L2)(HL2) luminescence spectra with time delay according to the two different methods57: (i) from the position of the short wavelength edge of the phosphorescence band, which is taken as the value corresponding to the 0-0 transition58,59, and (ii) from the position of the maximum of the highest energy vibration band of the deconvoluted phosphorescence band60. In the present work the value obtained from the position of the maximum of the highest energy vibration band was used, as it was shown in 61 by some of us that this value allows predicting ability. Calculated triplet state values equals 17700 cm-1 for Gd(L1)(HL1) and 18500 cm-1 for Gd(L2)(HL2), which are a little higher than the previously reported53 value for unsubstituted ligand H2L (T1(L2−) = 17100 cm−1.).

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Diffuse reflection spectroscopy The diffuse reflection (DR) spectra of the complexes were obtained in order to determine the presence of ligand to metal charge transfer (LMCT) state, namely the state [(Ln)-…M2+], in which the electron transfer from the ligand to the metal ion occurs. This state can participate in the energy transfer processes and can strongly influence the luminescence properties of europium and ytterbium complexes, so the determination of its presence or absence is an important task in a discussion of sensitization and quenching mechanisms. The DR spectra of Ln(L1)(HL1) (Ln = Eu, Gd, Yb) and Ln(L2)(HL2) (Ln = Gd, Eu, Yb, Lu) are presented in the Figure 5a,b. The broad band, corresponding to the ligand absorption in the range from 200 to 420 nm, is dominating all the spectra, the absence of ionic lanthanide absorption bands is due to the extremely large molar absorption coefficient of the organic ligands (ε(H2L1) = 19300 M-1·cm-1, ε(H2L2) = 17600 M-1·cm-1, see ESI). It can be found in europium and ytterbium complexes by comparison of DR spectra of Ln(Ln)(HLn) (Ln = Eu, Yb, n = 1,2) with DR spectra of lutetium or gadolinium complexes, in which LMCT state, if present, has too high energy62. In the spectrum of Eu(L2)(HL2) there is a broad additional band, which can be attributed to the presence of the LMCT band. The presence LMCT state can be shown using the classical approach11,63,64, namely, the direct subtraction of the DR spectrum of Gd or Lu complex, in which LMCT state has too high energy62, from DR spectrum of Eu or Yb complex, in which LMCT state has relatively low energy62. Indeed, the difference between the spectra of Eu(L2)(HL2) and Gd(L2)(HL2) consists of the high intensity single band with the maximum at 460 nm (21700 cm–1, Figure 5c). This fact allows 1,0

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us to suggest the presence of LMCT state in Eu(L2)(HL2) with the energy of ca. 21700 cm–1. This state has almost the same energy as the singlet state of organic ligand (S1((L2)2–) = 20400 cm–1, see above), thus, the energy exchange between LMCT and S1 states can occur. According to Faustino et al65 , if the LMCT state in europium complex possess the same energy as the ligand states (singlet or triplet) or slightly lower, the energy transfer between the S1 or T1 and LMCT state can result in the significant quenching of europium luminescence. Thus, we expect that europium luminescence in Eu(L2)(HL2) will be quenched due to the presence of LMCT state. At the same time, DR spectra of Gd(L1)(HL1), Eu(L1)(HL1), Yb(L1)(HL1), as well as of Gd(L1)(HL1), Yb(L2)(HL2), Lu(L2)(HL2), do not demonstrate significant differences. The differences between these DR spectra (see ESI, Figures 10-12) indicate only small bands in the range 400-500 nm of the almost the same intensity as the intensity of the noise, and much lower than the intensity of the band in Figure 5c. These bands can be attributed to the differences in lanthanide ionic radii, which can result in the shift of absorption band position, or to the possible differences in particle sizes or aggregation states of the complexes. It does not allows us to make any solid conclusions about the absence of charge transfer states in complexes Eu(L1)(HL1), Yb(L1)(HL1) and Yb(L2)(HL2), however, we can assume that LMCT states in these complexes, if present, has higher energy than LMCT state in Eu(L2)(HL2). According to Faustino et al 65, if the energy of LMCT state in europium complex is higher than the energy of ligand S1 level, the presence of this state should not decrease the quantum yield value of lanthanide luminescence. Thus, we assume that the charge transfer states in Eu(L1)(HL1), Yb(L1)(HL1) and Yb(L2)(HL2), if present, does not influence lanthanide luminescence.

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Luminescence of europium complexes The luminescence spectra of Eu(L1)(HL1) and Eu(L2)(HL2) at 298 and 77 K are represented in Figure 6. Both complexes possess broadband ligand luminescence at 298 K, while europium ionic luminescence is either absent (in Eu(L1)(HL1)) or is of low intensity (in Eu(L2)(HL2)). This means that the quenching processes effectively take place in these complexes. However, the temperature behaviour of these complexes is significantly different: Eu(L1)(HL1) demonstrates intense ionic europium luminescence at 77 K while the luminescence spectrum of Eu(L2)(HL2) at 77 K is very similar to the spectrum at 298 K and consists of both ligand and europium luminescence. It proves that the mechanisms of europium luminescence quenching in these complexes are significantly different. To determine the nature of these processes, we investigated europium luminescence more deeply. From the ionic europium luminescence bands of Eu(L1)(HL1) and Eu(L2)(HL2), which correspond to 5D0→7FJ (J = 0–4) transitions of Eu3+ ion, the values of europium radiative lifetimes were calculated66,67: 𝐼tot 1 (1 = 14,65 × 𝑛3 × 𝐼 (s ―1) , 𝜏rad MD ) where Itot/IMD is the ratio of the total integrated emission from the 5D0 europium level to the 7FJ manifold (J = 0–6) to the integrated intensity of the magnetic dipole (MD) transition 5D →7F , and n is the refraction index; it was taken to be 1.5, 0 1 as it was proposed in 6 as a typical value for Ln(III) complexes with organic ligands, allowing estimating the europium radiative lifetime. Europium radiative lifetimes, roughly determined with different experimental error due to the different spectra quality, were found to be the same in both complexes and equaled to 2.0 ± 0.2 ms for Eu(L1)(HL1) and 2 ± 1 for Eu(L2)(HL2). This is not surprising given very similar europium coordination environment in both complexes.

( )

Two types of quenching processes most likely take place: firstly, quenching involving additional states, first of all, charge transfer states. Based on diffuse reflection spectra data (see above), the relatively low-energy ligand-to-metal charge transfer (LMCT) state was proposed in Eu(L2)(HL2).We suggested that this state can participate in energy transfer processes, resulting in quenching of europium luminescence, which explains the luminescence spectra of Eu(L2)(HL2). Secondly, taking into account the low energy gap between the ligand triplet state values (T1((L1)2–) = 17700 cm-1, T1((L2)2–) = 17500 cm–1) and the europium 5D0 level (17200 cm-1), the europium luminescence can be quenched due to the temperature activated back energy transfer 5D0 → T1. This process must strongly depend on temperature, so in order to determine the presence or absence of this process in europium complexes, the luminescence spectra of Eu(L1)(HL1) and Eu(L2)(HL2) were obtained in the temperature range from 77 to 298 K (Figure 7). The luminescence of Eu(L2)(HL2) (Figure 7a) almost does not depend on temperature, which is in agreement with the LMCT state presence. At the same time, the europium luminescence intensity in the spectra of Eu(L1)(HL1) (Figure 7b) rapidly decreases down to complete absence as the temperature increases from 77 K to room temperature. While luminescence of Eu3+ ion in Eu(L1)(HL1) strongly depends on temperature, the ligand luminescence remains almost constant (see ESI, Figures 13-14). The ligand luminescence band in Eu(L1)(HL1) spectra is not seen compared to intensive europium luminescence at low temperatures, while it dominates the spectra above 180 K.


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a)

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Figure 7. Luminescence spectra of the a) Eu(L2)(HL2), b) Eu(L1)(HL1) in powder at the range from 77 K to 298 K (λex = 337 nm).

Temperature-activated back energy transfer in Eu(L1)(HL1) (Figure 8Figure 7a) can be described by the classical Mott– Seitz model68,69 that considers the competition between radiative transition and non-radiative back energy transfer. The dependences of the integrated ionic europium luminescence intensity (I) on temperature in Eu(L1)(HL1) (Figure 8Figure 7b, see ESI for integration details), according to this model, is given by Equation (2), which was extended to the case of lanthanide coordination compounds 22,23,53,59,64,70: 𝐼0 𝐼= , ―𝐸a (2) 1 + 𝐴 ∙ 𝑒𝑥𝑝( ) 𝑘𝑇 where A is related to the ratio between the nonradiative back energy transfer (at T = 0) and radiative processes rates, k is the Boltzmann constant, I0 is the beam intensity at T=0 K and Ea is the activation energy of the de-excitation channel with respect to the energy of the 5D0 level. In order to minimize the number

of fitting parameters and simplify the function, the equation (2) was written in logarithmic form: 𝐸a1 (3) 𝑙𝑛(𝐼) = 𝑐𝑜𝑛𝑠𝑡 + . 𝑘𝑇 In this equation, const = ln(I0) – ln(A), the assumption that ln(I0/I–1) ≈ ln(I0/I) was done. Equation (3) is a linear function, and the activation energy value Ea = 800 ± 200 cm–1 of back energy transfer in Eu(L1)(HL1) was obtained by the least squares fit of ln(I) on reciprocal temperature (Figure 8b). The Ea value coincides very good with the energy gap [T1-5D0] = 500 cm–1, that proves the presence of back energy transfer in Eu(L1)(HL1). The similar situation was observed in previously studied by us Eu(L)(HL) and Eu(HL)2Cl 53, where low-lying ligand triplet states (T1(HL-) = 19 400 cm−1 and T1(L2-) = 17 100 cm−1) resulted in thermally activated back energy transfer processes from 5D0 europium(III) level to T1 and strong dependence of europium luminescence intensity on temperature. 18

Experimental Fit

2.5x107 16

ln(I)

Integral Itensity (countsnm/sec)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.0x107

14

1.5x107 12 1

1/T (K )

7

1.0x10

0.006

10

180 160

0.007

140

0.008

0.009

120

0.010

0.011

100

0.012

80

T (K)

5.0x106

0.0

80

a)

Ea = 800 cm-1

100

b)

120 140 Temperature (K)

160

180

Figure 8. a) The scheme of energy transfer process in Eu(L1)(HL1), b) The temperature dependence of the integrated europium luminescence intensity (I) in Eu(L1)(HL1); Inset: the dependence of ln(I) on reciprocal temperature (T–1). Black dots – experimental values, Red lines – fit by Equation (3) (Adj. R2 = 0.971).



thermometers20,74–78, and the calculated sensitivity values (Sr calc.) according to the Equation (7) were compared with experimental values (Sr exp.) published in literature (Table 1). It is necessary to notice that the Equation (7) was obtained for the three-level system with the assumption of the temperature dependence dominance of one transition, and it is exactly the formula obtained if the LIR parameter is described by the Boltzmann law governing the population of two thermallyactivated levels, which is applied for a three level-system. The calculated sensitivity values (Sr calc.) demonstrate very good agreement with experimental sensitivity values (Sr exp.). The relative difference (the difference between Sr calc. and Sr exp. divided by the Sr exp. value) does not exceed 20%. Thus, the obtained Equation (7) allows to predict the sensitivity values for three-level luminescence thermometer system in case of efficient back energy transfer and/or high temperature. From the other side, according to this formula, the sensitivity linear depends on the activation energy, which determines the sensitivity of such a system. It signifies that the sensitivity values of terbium-europium luminescence thermometer (Ea = [Т5D4(Tb3+)-5D0(Eu3+)] = 3200 cm-1) in physiological range, which is one of the most important temperature range for luminescence thermometer design, equals 0.5 %/K. Indeed, the experimentally observed sensitivity of previously published terbium-europium terephthalates78 or fluorides24 is about 0.5%/K. Thus, to reach a high sensitivity in physiological range it is necessary to move from three-level system to more complicated system. For example, due to the effective triplet energy value of the ligand, Tb0.957Eu0.043(cpda) (H3(cpda) = 5-(4-carboxyphenyl)-2,6-pyridinedicarboxylic acid) possesses the sensitivity value up to 16%/K at 300 K 73.

600 12 500 10 400 8 300

6

200

Sensitivity (%K1)

Luminescence thermometer based on Eu(L1)(HL1) Such a pronounced temperature dependence of Eu(L1)(HL1) luminescence allows to consider this compound as a candidate for luminescence thermometry. The ratio of europium luminescence intensity at 612 nm to the ligand luminescence intensity at 565 nm was selected as the signal LIR = IEu/ILig (Luminescence Intensity Ratio, Figure 9). The thermometer based on Eu(L1)(HL1) can be effectively used below 180 K, when the europium luminescence intensity is sufficient to be compared with the intensity of ligand luminescence (see ESI, Figure 13). The important characteristic of the temperature dependent luminescence is its relative thermal sensitivity, which indicates the relative change of the thermometric parameter per degree of temperature change and is defined by Equation (4)22,23,71: 1 𝑑 𝐿𝐼𝑅 (4) 𝑆𝑟 = 𝐿𝐼𝑅 𝑑 𝑇 While the typical sensitivity values usually do not exceed a few percent, Eu(L1)(HL1) possesses the sensitivity value up to 12%/K (at 125 K, Figure 9) which is one of the highest values obtained to date and the highest value at the temperature range 100 – 140 K(the highest values are 31%/K at 4 K72 and 16%/K at 300 K23,73). The dependence of europium luminescence intensity on temperature is described by the Equation (2), the ligand luminescence intensity almost does not depend on temperature (see ESI, Figures 14). It allows us to write the LIR as follows: 𝐼𝐸𝑢(𝑇) 𝐼0 1 𝐿𝐼𝑅 = = · 𝐼𝐿𝑖𝑔(𝑇) 𝐼𝐿𝑖𝑔 ―𝐸a (5) 1 + 𝐴 ∙ 𝑒𝑥𝑝( ) 𝑘𝑇 Using the Equation (5), the sensitivity can be written as follows: 𝐴𝐸a 1 𝑆𝑟(𝑇) = 2 · (%/𝐾) 𝐸a (6) 𝑘𝑇 𝐴 + 𝑒𝑥𝑝 ( ) 𝑘𝑇 This equation describes the sensitivity dependence on temperature depending on parameters A, Ea of three-level luminescence thermometer with the assumption of the temperature dependence dominance of one transition (see ESI for analysis of the formula). One particular case of Equation (6) deserves consideration. If A >> exp(Ea/kT), that can be if the back energy transfer is an efficient process and/or the temperature is high, the Equation (6) simplifies to the Equation (7). 𝐸𝑎 𝑆𝑟 = 2 (%/𝐾) (7) 𝑘𝑇 This formula allows to calculate the sensitivity value depending on only Ea. To examine whether the formula (7) describes the real sensitivity behaviour, the sensitivity values were calculated for the published luminescence

LIR (IEu/ILig)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 19

4

100

2

0

0 80

100

120

140

160

180

Temperature (K)

Figure 9. LIR and sensitivity values of Eu(L1)(HL1)-based luminescent thermometer.


Page 9 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. The experimental and calculated according to the Equation (7) sensitivity values Sr. Ref.

Compound

20

Eu0.02Gd0.98(dsb)

20

Tb0.09Eu0.05Gd0.86(dsb) asd

Ligand SO3H

HO3S

CO2H

Ea (cm–1)

T (K)

Sr exp. (%·K-1)

Sr calc. (%·K-1)

13[a]

20[f]

4.64

4.68

210[a]

65[f]

7.14

7.16

4600[b]

180[f]

1.84

2.0

3600[c]

180[f]

1.40

1.6

3200[d]

150–250[g]

1.27

1.37

3200[d]

160–320[g]

1.05

1.13

1700[e]

293[f]

0.31

0.29

7400[e]

293[f]

1.28

1.24

3200[d]

313[f]

0.40

0.47

3200[d]

318[f]

0.37

0.46

H3dsb

74

{[Tb(cpbOH)(H2O)2](cpb)}∞

74

{[Tb(cpbOH)(H2O)2](cpb)}∞

B(OH)3

HO2C -

[HcpbOH]

75

Tb0.999Eu0.001(bpdc) NH2 N

75

Tb0.999Eu0.001(bpdc)(ad)

HO2C

N H

H2bpdc

76

N

CO2H

Eu@Zr6(μ3-O)4(OH)4(bpydc)12

N

ad

HO2C

CO2H N

N

H2bpydc

77

[Eu2(qptca)(NO3)2(DMF)4] (CH3CH2OH)3(perylene)

HO2C

CO2H

H4qptca

HO2C

24

CO2H

[email protected] HO2C

CO2H

H2tph

78

Tb0.99Eu0.01(tph)1.5(H2O)2 HO2C

CO2H

H2tph

[a] The activation energy were calculated in

20.

[b] The activation energy was calculated as Ea = [Т1-5D4(Tb3+)], T1 was calculated corresponding to the maximum of the first phosphorescence band in gadolinium complex spectrum. [c] The activation energy was calculated as Ea = [Т1-5D2(Eu3+)], T1 was calculated corresponding to the maximum of the first phosphorescence band in gadolinium complex spectrum. [d] The activation energy was calculated as Ea = [5D4(Tb3+)-5D0(Eu3+)]. [e] The activation energy was calculated as Ea = [Т1-5D0(Eu3+)], T1 was calculated corresponding to the maximum of the first phosphorescence band in gadolinium complex spectrum. [f] The temperature corresponds to the maximum value of Sr, published in the work. [g] The average Sr value of the temperature range was calculated.



Yb(L2)(HL2)

Yb(L1)(HL1)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 19

900

950

a)

1000 1050 Wavelength (nm)

1100

b)

900

950

1000

1050

1100

Wavelength (nm)

Figure 10. Luminescence spectra of a) Yb(L1)(HL1), b) Yb(L2)(HL2) in powder (λex = 365 nm).

Infrared luminescence Another interest in the investigation of the lanthanide complexes with Schiff bases is their ability to sensitize ytterbium luminescence, so infrared luminescence upon through-ligand excitation of ytterbium complexes Yb(L1)(HL1) and Yb(L2)(HL2) was studied. Both Yb(L1)(HL1) and Yb(L2)(HL2) luminescence spectra (Figure 10) demonstrated typical Yb3+ ion emission, corresponding to 2F 2 7/2 → F5/2 transition. Quantum yield (QY) values of Yb(L1)(HL1) and Yb(L2)(HL2) in powder achieved 0.5±0.2 % and 0.9±0.2 %, correspondingly (Table 2). Although these values are quite high for NIR luminescence, as the typical values of NIR QY do not exceed 1% with few exceptions 32,55,79–86, the obtained QY values are lower than QY values of the ytterbium complexes with H2L ligand that reached 1.4% 53. In the case of Yb(L1)(HL1) such a decrease can be connected with the presence of –OH group in the ligand structure, which is wellknown as a luminescence quencher 13,25,34,87–89. The decrease of the quantum yield value of Yb(L2)(HL2) can not be connected with vibrational quenching, as it is a temperature dependent process, and the luminescence intensity of Yb(L2)(HL2) absolutely does not depend on temperature (Figure 11). To understand the factor limiting quantum yield values, we calculated both the sensitization efficiency 𝜂𝑠𝑒𝑛𝑠 and internal quantum yield 𝑄𝑌𝑌𝑏 𝑌𝑏, which product is the overall quantum 𝑌𝑏 yield 𝑄𝑌𝐿𝑌𝑏 = 𝜂𝑠𝑒𝑛𝑠 × 𝑄𝑌𝑌𝑏. Internal quantum yield equals the ratio between observed and radiative lifetimes 𝑄𝑌𝑌𝑏 𝑌𝑏 = 𝜏𝑜𝑏𝑠 𝜏𝑟𝑎𝑑. Observed lifetimes were obtained to be 6±1 and 12 ±1 μs for Yb(L1)(HL1) and Yb(L1)(HL1) in powder, respectively (see Table 2), while for ytterbium(III) the radiative lifetime can also be calculated from the absorption spectrum corresponding to the emission spectrum with the help of the modified Einstein’s equation[57] 1 𝜏𝑟𝑎𝑑

= 2303 ×

8𝜋𝑐𝑛2𝜈2𝑢𝑙 (2𝐽 + 1) 𝑁𝐴

∫𝜀(𝜈)𝑑𝜈 ,

(2𝐽′ + 1)

DMSO (see ESI), the radiative lifetimes were calculated to be the same 6 ±1 μs for both complexes (Table 2). Coincidence of these values are in agreement with the same coordination environment of ytterbium ions, according to the crystal structure data (Figure 2). Assuming that the radiative lifetimes of ytterbium complexes in solution is the same as in powders, we calculated 𝜏𝑜𝑏𝑠 the internal quantum yield values 𝑄𝑌𝑌𝑏 𝑌𝑏 = 𝜏𝑟𝑎𝑑 (Table 2). It turned out that, as expected, the limiting factor was the internal quantum yield, which equalled ca. 2.2% for Yb(L2)(HL2) and below 1% for Yb(L1)(HL1). Additional decrease of the QYYbYb value in case of Yb(L1)(HL1) is definitely connected with the presence of the highly quenching OH-group. Such low values of QYYbYb of both complexes is connected with the ease of Yb luminescence quenching. 𝑌𝑏

The sensitization efficiencies 𝜂𝑠𝑒𝑛𝑠 = 𝑄𝑌𝐿𝑌𝑏/𝑄𝑌𝑌𝑏 of Yb by both ligands were almost the same within experimental error (~50%, see Table 2), that is in agreement with the same ligand triplet state values. These values are rather high for infrared luminescence. The sensitization efficiency values of ytterbium ion are rarely reported in the literature, and among published the high value can be found (i.e. 100% in 90), usually these values do not exceed several percentages14, if published.

(8)

where c is the speed of light in vacuum (cm sec-1), n is refractive index, NA is Avogadro’s number, J and J’ are the quantum numbers for the ground and excited states, respectively, ∫𝜀(𝜈)𝑑𝜈 is the integrated spectrum of the f-f ∫𝜈𝜀(𝜈)𝑑𝜈

transition, 𝜈2𝑢𝑙 = ∫𝜀(𝜈)𝑑𝜈 is the barycenter of the transition. From absorption spectra of Yb(L1)(HL1) and Yb(L1)(HL1) in


Page 11 of 19

Figure 11. Luminescence of Yb(L2)(HL2) in powder in the range from 77 K to 298 K (λex = 365 nm).

obtained for solutions while quantum yields were obtained for powders of the complexes, it does not allow us to directly calculated the brightness. However, comparing the ε and QY values of the complexes separately, we can conclude that the brightness of the complexes is mostly determined by the QY values, because ε values of the complexes are very similar due to the similar ligand structure. Thus, Yb(L2)(HL2) should posses higher brightness than Yb(L1)(HL1), while both complexes should posses less brightness than previously published complexes with H2L ligand53.

Table 2. Overall (QYLYb) and internal (QYYbYb) quantum yields, radiative (τrad) and observed (τobs) luminescence lifetimes, sensitization efficiency (ηsens) and maximum absorption coefficient (εmax) of ytterbium complexes. Compound

Yb(L1)(HL1)

Yb(L2)(HL2)

QYLYb ±0.2 (%)[a]

0.5

0.9

τobs ±1 (μs) at 298 K[a]

6

12

0.6

0.6

1.0

2.2

60

40

~38000

31000

τrad ±0.1 (ms) at 298 ±0.2

(%)[c]

ηsens ±30 (%)[d] εmax ± 3000 [a]

M-1cm-1 [e]

QYLYb

OLED based on Yb(L2)(HL2) High solubility of Yb(L2)(HL2) and rather high quantum yield, together with the expected charge carrier mobility due to the presence of both electron-poor and electron-rich fragments allowed testing this material as emitting layer in a host-free OLED. The obtained OLED with the heterostructure ITO/PEDOT:PSS (50 nm)/PVK (13 nm)/Yb(L2)(HL2) (29 nm)/TPBi (11 nm)/LiF(1 nm)/Al (43 nm) demonstrated intense NIR luminescence intensity, corresponding to the Yb(L2)(HL2) emission. Rather high current density of the obtained diode with the host-free emission layer (Figure 12) proves that indeed the emission layer exhibits charge carrier mobility. The presence of the parasitic band at ca. 400 nm corresponds to the emission of PVK and TPBi, witnessing not perfectly balanced charge carriers. Despite this, the obtained luminescence intensity, as well as efficiency, is rather high: so, 8.25 µW/cm2 were reached at 10V and 70.8 mA/cm2, while maximum efficiency reached 50 µW/W at 5 V and external quantum efficiency achieved 0.02% at 5 V for Yb-based luminescence. This is a rather high value of Yb-based NIR luminescence intensity. Indeed, except for several papers32,91,92, the maximum efficiency of Yb-based OLEDs obtained worldwide do not exceed 10 µW/W 80,93,94. It is particularly important that this value was obtained for the complex with moderate quantum yield, which proves the dramatic importance of the charge carrier mobility for the use in OLED.

and τobs were measured for complexes in powder.

[b] Calculated from the absorption spectra of Yb(Ln)(HLn) (n = 1, 2) in DMSO (see ESI) according to Equation (8). [c] Were 𝜏𝑜𝑏𝑠

calculated

according

to

the

formula

𝑄𝑌𝑌𝑏 𝑌𝑏 =

𝜏𝑟𝑎𝑑. An assumption that τrad for solution of complexes is the same as for powders was made. [d] Were calculated ηsens = QYLYb / QYYbYb.

according

to

the

formula

[e] For Yb(L2)(HL2), calculated for acetonitrile solution. For Yb(L1)(HL1), roughly estimated like double molar absorption coefficients of H2L1 in DMSO(see ESI).

Although the quantum yield is a widely discussed parameter, for photoluminescent applications, the so-called parameter Brightness (B), which is also known as Luminosity, is of practical interest, which describes not only the ability of complex to emit light but also the excitation ability. Brightness is defined by the formula[13] B = ε·QY, (9) where ε is a molar extinction coefficient and·QY is a quantum yield of the complex. Because the absorption coefficients were

60000 55000 50000 45000 40000

2

50

Efficiency (µW/W)

65000

35000 30000 25000 20000

F5/22F7/2

60

120

50

100

40

80

30

60

20

40

10

20

0

0

40

8V

Efficiency (µW/W)

70000

30 20 10 0

0

10 20 30 40 50 60 70 80 2 I (mA/cm )

7V 6V

15000

2

Yb

K[b]

I (mA/cm )

QYYb

Intensity (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10000

5V

5000 0

200

a)

400

600

Wavelength (nm)

800

1000

0

b)

2

4

U (V)

6

8

10

Figure 12. a) Electroluminescence spectra at different voltages and current-efficiency dependence, b) current-voltage and currentefficiency curves of the OLED with heterostructure ITO/PEDOT:PSS/PVK/Yb(L2)(HL2)/TPBi/LiF/Al.



CONCLUSIONS We synthesized lanthanide complexes with two 2-(tosylamino)-benzylidene-N-(aryloyl)hydrazones (H2L1, 2 aryloyl = 2-hydroxybenzoyl; H2L , aryloyl = Isonicotinoyl) Ln(L1)(HL1) and Ln(L2)(HL2) and investigated their structure and luminescene properties in comparison with previously published53,54 complexes with 2-(tosylamino)-benzylidene-N(benzoyl)hydrazone Ln(L)(HL) and Ln(HL)2Cl. Crystal structure of Yb(L2)(HL2)·0.5(C2H5OH) was determined from single crystal XRD, while structure of Yb(L1)(HL1) was obtained from powder data by Rietveld refinement. Both complexes are built from the same mononuclear species [Yb(Ln)(HLn)] (n = 1, 2), similar to those found in the structures of various complexes with L2- and (HL)-. Different luminescence quenching mechanisms of Eu(Ln)(HLn) for n = 1 or 2 results in the different luminescence properties of europium complexes. In case of Eu(L2)(HL2), the europium luminescence was quenched due to presence of LMCT state, which was assumed based on diffuse reflectance spectra data, and this complex possesses lowintensive europium luminescence, independing on temperature. At the same time, due to the presence of temperatureactivated back energy transfer from 5D0 europium level to the ligand triplet level, Eu(L1)(HL1) possesses strongly temperature-depend luminescence, which intensity was described by Mott–Seitz model (Equation (2)). It allowed using this complex for luminescent thermometry, and the sensitivity value reached 12%/K at 125K, which is the highest in this temperature range and 3rd highest among all the published values. The theory of luminescence thermometry for three-level systems (ground state and two excited states) was proposed, which allows predicting sensitivity with high accuracy (Equation (7), error below 20%). In particular, it was calculated that sensitivity of Tb-Eu thermometers in physiological range is limited by ca. 0.5%/K. Ytterbium complexes demonstrated high luminescence intensity in the NIR range. This is due to rather high quantum yield and either high absorption in case of photoluminescence or charge carrier mobility in case of electroluminescence. The latter allowed obtaining NIR emitting host-free OLED with heterostructure ITO/PEDOT:PSS/PVK/Yb(L2)(HL2)/TPBi/LiF/Al which demonstrated remarkable efficiency up to 50 µW/W at 5V. EXPERIMENTAL SECTION Synthesis of the ligands Synthesis of 2-(tosylamino)-benzylidene-N(2-hydroxybenzoyl)-hydrazone (H2L1). To the solution of 2tosylaminobenzaldehyde (2.75 g, 10 mmol) in ethanol (50 ml) the 2-hydroxybenzhydrazide (1.52 g, 10 mmol) in ethanol (20 ml) was added. The mixture was heated under stirring for 2 hours. The precipitate was filtered, washed 2x5 ml with ethanol, recrystallized from ethanol : chloroform (2 : 1) mixture and dried in drying cabinet at 120 ̊C. Yield 3.68 g (90%). Colorless needle crystals, m.p. 209-210 ̊C. Elemental analysis. Calcd. (%): C 61.60, H 4.68, N 10.26, S 7.83; Found (%): C, 61.68; H, 4.60; N, 10.30; S, 7.95. 1H NMR spectra in DMSO, δ (ppm): 2.31 (3Н, s, СН3), 6.98-7.03 (2H, m, CHAr), 7.18-7.22 (1H, t, CHAr), 7.28-7.37 (4H, m, CHAr), 7.46-7.50 (1H, t, CHAr), 7.62-7.67 (3H, m, CHAr), 7.92-7.95 (1H, d,

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CHAr), 8.54 (1H, s, CH=N), 11.00 (1H, s, NH or OH), 11.83 (1H, s, NH or OH), 12.01 (1H, s, NH or OH). IR spectra, ν (cm-1), only most characteristic bands are presented: broad 3356 (NH), broad 3159 (OH), 1633 (С=О), 1606 (СH=N), 1327 (as SO2), 1147 (s SO2). Synthesis of 2-(tosylamino)-benzylidene-N(isonicotinoyl)-hydrazone (H2L2). To the solution of 2tosylaminobenzaldehyde (2.75 g, 10 mmol) in ethanol (50 ml) the isonicotinic acid hydrazide (1.37 g, 10 mmol) in ethanol (10 ml) was added. The mixture was heated under stirring for 2 hours. The precipitate was filtered, washed 2x5 ml with ethanol, recrystallized from ethanol-chloroform (2 : 1) mixture and dried in drying cabinet at 120 ̊C. Yield 3.3 g (86%). White crystals, m.p. 215-216 ̊C. 1H NMR spectra in DMSO, δ (ppm): 2.32 (3Н, s, СН3), 7.19-7.24 (2H, t, CHAr), 7.33-7.36 (3H, t, CHAr), 7.64-7.69 (3H, t, CHAr), 7.87-7.89 (2H, d, CHAr), 8.61 (1H, s, CH=N), 8.82 (2H, d, CHAr), 10.89 (1H, s, NH), 12.34 (1H, s, NH). IR spectra, ν (cm-1), only most characteristic bands are presented: broad 3208 (NH), 1690 (С=О), 1666, 1607 (H=N), 1341 (as SO2), 1159 (s SO2). The 2-hydroxybenzhydrazide and isonicotinic acid hydrazid are obtained from Alfa Aesar. Syntheses of the lanthanide complexes Synthesis of Ln(L1)(HL1). A freshly prepared lanthanide hydroxide (0.25 mmol) was added to a hot solution of 0.2 g (0.55 mmol) H2L1 in 50 ml ethanol. The mixture was heated under stirring for 24 hours resulted in yellowish crystalline precipitate, which was filtered off, washed with ethanol and air-dried. Elemental analysis. Lu(L1)(HL1), Calcd. (%): C, 50.91; H, 3.56; N, 8.48; Found (%): C, 50.62; H, 3.57; N, 8.44. Yb(L1)(HL1), Calcd. (%): C, 51.01; H, 3.57; N, 8.50; Found (%): C, 50,64; H, 3,71; N, 8,36. S, 5,76. Er(L1)(HL1), Calcd. (%): C, 51,31; H, 3,59; N, 8,55; Found (%): C, 50,59; H, 3,78; N, 8,37. Gd(L1)(HL1), Calcd. (%): C, 51,84; H, 3,63; N, 8,64; Found (%): C, 51,53; H, 3,79; N, 8,43. Eu(L1)(HL1), Calcd. (%): C, 52,12; H, 3,64; N, 8,68;Found (%): C, 51,87; H, 3,83; N, 8,44. Sm(L1)(HL1), Calcd. (%): C, 52.21; H, 3.65; N, 8.70; Found (%): C, 52,81; H, 3,75; N, 8,56. Synthesis of Ln(L2)(HL2). To a solution of H2LPy (0,5 mmol) in 50 ml ethanol-acetonitrile (2:1) the excess of a freshly prepared lanthanide hydroxide (0,5 mmol) was added. The obtained mixture was heated under stirring for 24 hours resulted in yellowish solution of complex, containing precipitate of unreacted lanthanide hydroxide. The mixture was filtered off, and obtained clear solution was evaporated to dryness resulted in yellowish powder. Elemental analysis. Lu(L2)(HL2), Calcd. (%): C, 50,00; H, 3,65; N, 11,66; Found (%): C, 50,15; H, 3,64; N, 11,61. Yb(L2)(HL2), Calcd. (%): C, 50,10; H, 3,47; N, 11,69; Found (%): C, 50,01; H, 3,69; N, 11,89. Gd(L2)(HL2), Calcd. (%): C, 50.94; H, 3.53; N, 11.88; Found (%): C, 50,51; H, 3,64; N, 11,99. Eu(L2)(HL2), Calcd. (%): C, 51.23; H, 3.55; N, 11.95; Found (%): C, 51,02; H, 3,50; N, 11,87. Crystal structure determination Yb(L2)(HL2)·0.5EtOH Single crystals of C41H36N8O6.5S2Yb [Yb(L2)(HL2)·0.5EtOH] were grown from EtOH. A suitable crystal was selected and kept on a Bruker II CCD diffractometer. The crystal was kept at 120 K during data collection. Using Olex2 95, the structure was solved with the


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ShelXS 96 structure solution program using Direct Methods and refined with the XL 96 refinement package using least square method. Crystal Data for [Yb(L2)(HL2)·0.5EtOH]. C41H36N8O6.5S2Yb (M =981.94 g/mol): monoclinic, space group P21/c (no. 14), a = 16.876(3) Å, b = 13.3570(19) Å, c = 19.197(3) Å, β = 108.490(3)°, V = 4103.8(10) Å3, Z = 4, T = 120 K, μ(MoKα) = 2.439 mm-1, Dcalc = 1.589 g/cm3, 47469 reflections measured (3.78° ≤ 2Θ ≤ 56.68°), 10208 unique (Rint = 0.1758, Rsigma = 0.1369) which were used in all calculations. The final R1 was 0.0583 (>2sigma(I)) and wR2 was 0.1441 (all data). The crystallographic data for Yb(L2)(HL2)·0.5EtOH were deposited in CCDC 1864563. Eu(L1)(HL1) The powder pattern of Eu(L1)(HL1) was measured on Bruker D8 Advance Vario diffractometer with LynxEye detector and Ge (111) monochromator, (CuKα1) = 1.54060 Å, θ/2θ scan from 4.0° to 90°, step size 0.007859°, in transmission mode, with the sample deposited between Mular films. The patterns were indexed using SVD-Index97 as implemented in TOPAS 4.2 software98. The obtained cell parameters were closest to the published structure of Lu(HL)2Cl 53. That is why we used structure of Lu(HL)2Cl as start model for further Rietveld refinement. The hydroxyl groups were added to the phenyl rings and the chlorine anion was deleted. Then the start model was refined using soft (parabolic) bond and angle restraints; the obtained distribution of the deviations of the bond lengths from restrained values (Δd) contained no outliers, indicating a consistent structural model according to approach outlined in 99. Crystal Data for Eu(L1)(HL1). C42H35EuN6O8S2 (M =967.86 g/mol): triclinic, space group P-1 (no. 2), a = 10.86215(15) Å, b = 11.41095(11) Å, c = 17.09812(16) Å, α = 84.6203(5)°, β = 75.4586(8)°, γ = 84.3682(9)°, V = 2036.22(4) Å3, Z = 2, T = 298 K, μ(CuKα~1~) = 12.495 mm1,Dcalc = 1.579 g. At average Δd of 0.010 Å (K =7) the 1 refinement converged to Rp/RP’/RWP/RWP’/RBragg values of 0.826/1.799/1.087/2.098/0.320 % with Rexp/Rexp’ of 0.668/1.290 %, GOF=1.627 (Figure 13). The crystallographic data for Eu(L1)(HL1) were deposited in CCDC 1864562.

Figure 13 The Rietveld fit for Eu(L1)(HL1). The experimental (blue line) and calculated (red line) powder patterns for Eu(L1)(HL1) and their difference (grey curve).

Photoluminescence spectra in the visible range were recorded on a multichannel spectrometer S2000 (Ocean Optics) using a nitrogen laser LGI-21 (λex = 337 nm) or diode laser (λex = 365 nm) as an excitation source at 298 K.

Photoluminescence spectra at 77 K were recorded on the same device by placing the sample in the liquid nitrogen cryostat. Photoluminescence spectra in the NIR range were measured using an Edinburgh Instruments FLS980 Fluorescence Spectrometer equipped with a 450 W xenon lamp. Both the excitation and emission 300 mm focal length monochromators were in the Czerny Turner configuration. The excitation arm was supplied with holographic grating of 1800 lines per mm, blazed at 250 nm. While the emission spectra were supplied with ruled grating, 1800 lines per mm blazed at 500 nm. The spectral resolution was 0.1 nm. The R5509-72 photomultiplier tube from Hamamatsu in nitrogen-flow cooled housing was used as a detector for the near infrared range. Quantum yields in NIR range were determined using the same equipment. To record the photoluminescence spectra in the range from 77 K to 298 K, the handcrafted facility using the heating element and the thermal control device was used (Figure 14). Into a vacuum liquid-nitrogen cryostat KP-15 M (1), a sample (2) was placed on the copper stage (3) which was, on the one hand, cooled by the cooling loop from stainless steel (4) connecting the liquid-nitrogen storage tank (5) and, on the other hand, heated by the handcrafted furnace from a constantan wire (d = 0.3 mm) (6). The heating was controlled by using a high precision temperature controller BTP-3 (7) which allowed the calculation based on the data obtained from a measuring thermocouple (type T) (8) and a reference thermocouple (type T) in liquid nitrogen (9). The measuring thermocouple voltage was showed by using a voltmeter V7-23 (10) and recalculated into temperature using the calibration scale. Photoluminescence spectra in the visible range were recorded on a multichannel spectrometer S2000 (Ocean Optics) (in visible range) or on a FLS980 Fluorescence Spectrometer (in NIR range) (11) using a nitrogen laser LGI21 (λex = 337 nm) (12) as an excitation source.

Figure 14. The scheme of facility for photoluminescence spectral measurements in the range from 77 to 298 K. 1 – Liquid-nitrogen cryostat KP-15 M; 2 – sample; 3 – copper stage; 4 – cool loop from stainless steel; 5 – liquid-nitrogen storage tank; 6 – handcrafted furnace from a constantan wire (d = 0.3 mm); 7 – high precision temperature controller BTP-3; 8 – measuring thermocouple (type T); 9 – reference thermocouple (type T) in liquid nitrogen; 10 – voltmeter V7-23; 11 – multichannel spectrometer S2000 (Ocean Optics) (in visible range) or FLS980



Fluorescence Spectrometer (in NIR range); 12 – nitrogen laser LGI-21 (λex = 337 nm).

Diffuse refection spectra were recoded using a PerkinElmer LAMBDA 950 spectrometer. Elemental analyses (C, H, N, S) were performed on a Vario Micro Cube analyzer (Elementar, Germany). Thermal analysis was carried out on a thermoanalyzer STA 409 PC Luxx (NETZSCH, Germany) in the temperature range of 20-1000 ºC in air, heating rate 10 º/min. IR spectra in the ATR mode were recorded on a spectrometer Spectrum One (Perkin-Elmer) in the region of 400-4000 cm-1. X-ray powder diffraction (XRD) measurements were performed on a on a Bruker D8 Advance diffractometer (Vario geometry) in the 2θ range of 4–80° equipped with a Cu Kα1 Ge(111) focusing monochromator and a LynxEye onedimensional position-sensitive detector. The powder X-ray diffraction patterns were indexed using TOPAS 5.0 software. Absorption spectra were obtained using Perkin Elmer LAMBDA 950 spectrometer. OLED manufacturing Substrate preparation. Substrates with pre-partened ITO of 12 Ohm/sq resistance were purchased from Lumtec Taiwan. Before spin-coating, the substrates underwent standard cleaning procedure of ultrasonication in KOH solution, bidistillated water, isopropanol for 15 minutes each followed by drying with nitrogen flow. Then the substrates were placed in an UV-cleaning chamber (Ossila UK) where additional cleaning and O3 – enrichment of ITO took place during 25 minutes in order to increase wettability of the substrates. Solutions spin-coating. In experiments we used a spin coater KW-4A by Chemat Technology operating in the air. To form PEDOT-PSS film (Lumtec LT-PS001), a 200 ml of aqueous solution was poured on the resting ITO-substrate, followed the rotation at 2000 rpm for 1 min. The obtained 50 nm PEDOT-PSS were dried at 100 C for 30 min in the air. 13 nm PVK (Lumtec LT-N4077) films were spin-coated on ITO/PEDOT-PSS from 5 g/l solution in toluene by applying 200 ml of solution on the resting substrate followed by 2000 rpm rotation for 1 min. The obtained structures were then dried at 100 C for 10 min in the air. The 3 g/l solution of Yb(L2)(HL2) in ethanol was filtered through 0.45 mkm syringe filter prior to deposition. Spincoating of 100 mkl of solution at 1250 rpm during 1 min in the air gives 29 nm film. The obtained structures of ITO/PEDOTPSS/PVK/Yb(L2)(HL2) were then moved to argon glove-box with O2 and H2O content lower than 10 ppm. The structures were finally dried at 100 C for 10 minutes. Thermal deposition. 15 nm TPBi (Lumtec LT-E302) film was thermally deposited in vacuum less than 10-3 Pa from a quartz cuvette heated by tantalum spiral. Then 1nm of LiF (Lumtec LT-E001) at rate 0.1 A/s and 40 nm of aluminum at rate 0.5 nm/s were thermally deposited through a mask to form four 12 mm2 pixels. The obtained devices were encapsulated with Star Technology UV-curable adhesive UVA-4103. Deposition rate was measured in situ by a deposition controller Leybold Inficon IC-6000 calibrated by NT-MDT atomic force microscope of Integra family. Thicknesses of spin coated films were also measured by NT-MDT atomic force microscope directly on an OLED structures.

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Measurements. The electroluminescence spectra were obtained with an Ocean Optics Maya 2000 Pro CCD spectrometer sensitive within 200-1100 nm. Current-voltage characteristics were obtained using two DT 838 Digital multimeters. OLED optical power was determined using a Coherent FieldMaxII Laser Power Meter with an optic filter removing visible part of the spectra.

ASSOCIATED CONTENT Supporting Information includes the absorption spectroscopy data, infrared spectroscopy data, thermal analysis of the complexes, comparison of diffuse reflectance spectra, details of the europium luminescence spectra processing, luminescence spectra of gadolinium complexes with time delay, lifetimes of gadolinium complexes luminescence, analysis of sensitivity formula, crystal structure data, X-ray powder diffraction patterns of lanthanide complexes, 1H NMR spectra of organic ligands. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Valentina V. Utochnikova [email protected]

Present Addresses † Faculty of Chemistry, Lomonosov Moscow State University, Russia, 119991, Moscow 1, GSP-1, 1-3 Leninskiye Gory.

Funding Sources This work was supported by Russian Science Foundation (17-7310072). OLED fabrication was supported by Russian Foundation for Basic Research (17-32- 80050).

ACKNOWLEDGMENT This work was supported by Russian Science Foundation (17-7310072). OLED fabrication was supported by Russian Foundation for Basic Research (17-32- 80050). The contribution of Centre for molecular composition studies of INEOS RAS is gratefully acknowledged.

ABBREVIATIONS DR, diffuse reflection; ESI, electronic supplementary information; H2L , 2-(tosylamino)-benzylidene-N-benzoylhydrazone; H2L1, 2(tosylamino)-benzylidene-N-(2-hydroxybenzoyl)-hydrazone; H2L2, 2-(tosylamino)-benzylidene-N-(isonicotinoyl)-hydrazone; LMCT, ligands-to-metal charge transfer; NIR, near infrared; OLED, organic light emitting diode; QY, quantum yield; XRD, X-ray diffraction.

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Lanthanide complexes with 2-(tosylamino)-benzylidene-N-(aryloyl

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