An unexpected phenomenon of intense luminescence of aqueous solutions of macromolecular europium complexes

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Yakimansky, Elena L. Krasnopeeva, Tatiana N. Nekrasova, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9513611/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Amphiphilic cylindrical brushes consisting of a cellulose backbone and grafted poly(methacrylic acid) chains (Cell-g-PMAA) with high grafting density were synthesized. Their interaction with europium ions in dilute aqueous solutions (0.002–0.02 wt%) was investigated. A comparative study of photophysical properties of (europium-phenanthroline) complexes with Cell-g-PMAA and (europium-phenanthroline) complexes with linear poly(methacrylic acid) was carried out. It was found that the intensity of Eu 3+ luminescence in the complexes with Cell-g-PMAA is an order of magnitude higher than the corresponding value for europium complexes with linear PMAA. It is suggested that solubilization of phenanthroline in the hydrophobic part of the brush (i.e., in the layer between the main chain and grafted chains) enhances its Eu 3+ binding efficiency, which, in turn, leads to the replacement of water molecules in the inner coordination sphere with phenanthroline molecules. In addition, the decrease in the mobility of grafted chain segments near the backbone “strengthens” the structure of the complex. The obtained results indicate that structural organization of a macromolecular ligand plays a significant role in the formation of europium ion complexes and contributes to the enhancement of photoluminescence. Macromolecular ligands Topology Luminescence Europium ions Aqueous solutions Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Along with the development of chemistry of low molecular weight coordination complexes of lanthanide ions, primarily Tb 3+ , Eu 3+ , Sm 3+ , Er 3+ , Yb 3+ , which demonstrate luminescence in the visible and near-infrared spectral regions [ 1 – 3 ], the chemistry of macromolecular complexes of lanthanides (MCL) attracts attention of researchers. MCL retain the unique optical properties of lanthanide ions, such as quasi-monochromatic emission (their luminescence band width is equal to 5–10 nm, while for organic chromophores it exceeds 100 nm), stability of emission over time (the absence of bleaching), and independence of the position of luminescence bands from the nature of a ligand and a solvent. In addition, they demonstrate large Stokes shifts, high values of excited state lifetimes, and independence of the shape of photoluminescence spectrum from the ligand nature for practically all lanthanides, with the exception of Eu 3+ ions, in whose spectra the Stark splitting of f -levels is observed (caused by a change in the crystal field of a ligand). At the same time, compared to low molecular weight complexes of lanthanide ions, MCL have a number of advantages; for example, they can be used to obtain mechanically strong and stable materials in the form of films, gels, coatings, to prolong the action of drugs in the body, etc. [ 3 ]. Varying the structure of a macromolecular ligand not only provides means for targeted modification of luminescent properties of MCL, but also offers a number of additional possibilities. For example, the use of biologically active comonomers or comonomers containing covalently attached drugs makes it possible to visualize the interaction of complexes with cells and monitor their distribution in organs and tissues, to prolong the action of biosensors and probes, which allows for a reduction in the dose of the administered drug [ 4 ]. Lanthanide radioisotopes are also of interest for medicine [ 5 ]. In the last decade, luminescent lanthanide complexes have been actively studied as promising materials demonstrating a wide range of antitumor activity [ 6 – 8 ]. Ligands play an important role in the coordination of the properties of the respective complexes and are particularly significant for biological, biochemical, and medical applications [ 9 ]. Therefore, the synthesis of new low-toxicity, water-soluble ligands that form stable luminescent complexes with lanthanide ions is of fundamental and practical interest. The authors of [ 10 , 11 ] demonstrated the prospects and effectiveness of using amphiphilic brushes in photodynamic therapy; these brushes consisted of polyimide or cellulose backbones, to which poly(methacrylic acid) chains were regularly grafted. Such copolymers are capable of solubilizing (incorporating) large organic molecules and organometallic complexes in aqueous media and can serve as nanocontainers. Diphilic macromolecular brushes with a polyimide backbone and poly(methacrylic acid) blocks in side chains bind lanthanide ions [ 12 ]. Their luminescent complexes may be of interest for fluorescence diagnostics and photodynamic therapy. In this work, the amphiphilic cellulose-g-poly(methacrylic acid) (Cell-g-PMAA) brush was used as a macromolecular ligand to obtain luminescent complexes with Eu 3+ ions. The influence of ligand topology on photophysical properties of the complex in dilute aqueous solutions was investigated. Experimental Materials Microcrystalline cellulose (MCC) with an average particle size of 50 µm (degree of polymerization ~ 330) was purchased from Acros Organics (Buchs SG, Switzerland). 2-Bromo-isobutyryl bromide (BiBB), 1-butyl-3-methylimidazolium chloride (BMIMCl) (ionic liquid), N,N-dimethylformamide (DMF) (solvent), pentamethyldiethylenetriamine (PMDETA), and tert -butyl methacrylate monomer (TBMA, 98%) were distilled twice under vacuum before use. Copper (I) bromide (CuBr) was purchased from Sigma Aldrich. Orthophosphoric acid (99%) used for acid hydrolysis was purchased from Saint-Louis, MS, USA. Trifluoroacetic acid, methylene chloride (reagent grade), tetrahydrofuran (THF) (chemically pure), ethyl alcohol, methyl alcohol, and potassium hydroxide were purchased from Vekton (Saint-Petersburg, Russia). Europium chloride hexahydrate (EuCl 3 ×6H 2 O) and 1,10-phenanthroline were purchased from Sigma Aldrich. Synthetic Procedures The synthesis of Cell-g-PMAA samples included three stages. Scheme 1 demonstrates the chemical route for preparation of this polymer brush. In the first stage, the macroinitiator Cell-BiB was prepared in ionic liquid (BMIMCl), and it was further used to polymerize tert -butylmethacrylate (TBMA) via ATRP mechanism, using CuBr/pentamethyldiethylenetriamine (PMDETA) catalytic system. Finally, thus prepared polymer brush Cell-g-PTBMA with cellulose backbone and poly(TBMA) side chains was subjected to acidic hydrolysis by CF3COOH in CH2Cl2, producing a water-soluble molecular brush Cell-g-PMAA with cellulose backbone and poly(methacrylic acid) side chains. The syntheses of the macroinitiator Cell-BiB, Cell-g-PTBMA and Cell-g-PMAA were carried out according to the method described in detail in [ 11 ] (see Supplementary material). Determination of macroinitiator composition The content of Br and C (ω(Br) and ω(C), in wt.% respectively) in macroinitiators was measured with energy dispersive X-ray (EDX) spectroscopy using a scanning electron microscope VEGA 3 SBH (Tescan, Czech Republic) equipped with an Aztec Energy X-act microanalysis system (Oxford Instruments, UK). The amount of isobutyroyl bromide per cellulose unit (n(BiB)/n(cell) = x see Scheme 1 ) was calculated as: $$\:x=\frac{\text{n}\left(\text{B}\text{i}\text{B}\right)}{\text{n}\left(\text{C}\text{e}\text{l}\text{l}\right)}=\frac{6\:\omega\:\left(Br\right)}{79.9\left(\frac{\omega\:\left(C\right)}{12}-4\frac{\omega\:\left(Br\right)}{79.9}\right)}$$ Preparation of [Cell-g-PMAA]/[PHEN]/[Eu] solutions A weighed amount (10 mg) of Cell-g-PMAA was dissolved in 1 mL of 0.1N NaOH; after dissolution, 9 mL of distilled water was added. The initial solution was used to prepare a series of solutions with concentrations varying from 0.03 to 0.5 mmol (8 solutions). Then, 1 mL of Eu 3+ /phenanthroline (PHEN) solution was added to each sample, in which concentrations [Eu 3+ ] = 2×10 − 4 mol/L, [PHEN] = 4×10 − 4 mol/L. The solution was left to stay for 1 h, then the measurements were taken. IR spectroscopy The IR spectra of samples were obtained at room temperature in the 400–4000 cm − 1 wavenumber range (resolution: 4 cm − 1 ; number of scans: 30) using a “Vertex 70” FTIR spectrometer (Bruker, Ettlingen, Germany) equipped with a ZnSe attenuated total reflection (ATR) attachment (“Pike Technologies”, Madison, WI, USA). During the registration of the ATR spectra, a correction was made that took into account light penetration depth as a function of wavelength. Gel permeation chromatography Determination of molecular weights of grafted PTBMA chains in Cell-g-PTBMA In order to determine molecular weights of grafted PTBMA chains in Cell-g-PTBMA, these side chains were cleaved from the backbone by means of an alkaline hydrolysis as described in Supplementary materials. The cleaved PTBMA side chains were analyzed by size-exclusion liquid chromatography (SEC) using an Agilent-1260 Infinity chromatographic complex equipped with PLgel (7.5 × 50 mm, 5 µm) guard column and two Agilent PLgel MIXED-C columns (7.5 ⋅ 300 mm, 5 µm). THF was used as eluent at flow rate 1 ml/min (isocratic mode) and column temperature 40°C. Molecular weight characteristics were determined from refractometric detection data using calibration with PS standards. Chromatographic data were analyzed using Agilent GPC/SEC Software version 1.2. Luminescence spectroscopy The excitation and photoluminescence spectra of the solutions, as well as the kinetic phosphorescence decay curves, were recorded using an LS-100 spectrofluorometer (PTI, Canada). The excitation spectra of photoluminescence were recorded at an emission wavelength of λ em = 615 nm. The photoluminescence spectra were recorded at an excitation wavelength of 299 nm. The lifetime of the excited state of Eu 3+ in complexes (τ phosph ) was determined from the kinetic phosphorescence decay curves. All measurements were performed in a quartz cuvette with an optical path length of 1 cm, in a thermostated cell at 25°C. Results and discussion Characterization of the synthesized Cell-g-PMAA copolymers Two Cell-g-PMAA samples, Cell-g-PMAA1 and Cell-g-PMAA2, were prepared and characterized. They were obtained by acidic hydrolysis of side chains of Cell-g-PTBMA1 and Cell-g-PTBMA2 samples, respectively. In turn, Cell-g-PTBMA1 and Cell-g-PTBMA2 samples were synthesized by ATRP of TBMA on macroinitiators Cell-BiB1 and Cell-Bib2, differing in the weight fraction of Br. molar fraction x of BiB-containing units (Scheme 1 ). According to EDX, the prepared macroinitiators Cell-BiB1 and Cell-Bib2 have 16 and 11 wt% Br, while carbon content was 46.9 and 50.2 wt.%, respectively. Calculations showed that sample 1 has an average of 10 grafting points per 25 cellulose monomer units, while sample 2 has 10 grafting points per 40 cellulose monomer units. From these data, molar fraction x of BiB-containing units (Scheme 1 ) and average monomer unit molecular weights for macroinitiators Cell-BiB1 and Cell-Bib2 were found (Table 1 ). Table 1 Compositions of macroinitiators Cell-BiB1 and Cell-Bib2. Sample x (Scheme 1 ) average monomer unit molecular weight, Da Cell-BiB1 0,40 222 Cell-BiB2 0,24 200 The molecular weights, M n , of grafted PTBMA chains in Cell-g-PTBMA polymer brushes, determined by GPC, were 16 and 19 kDa for samples Cell-g-PTBMA1 and Cell-g-PTBMA2, respectively, corresponding to M n = 9,7 and 11,5 kDa for side PMAA chains of Cell-g-PMAA1 and Cell-g-PMAA2, respectively (degrees of polymerization ~ 105 and ~ 127, respectively). The Cell-g-PMAA1 and Cell-g-PMAA2 samples were further characterized by the wt. fraction of PMAA side chains, using their IR spectra (Fig. 1 ). The Pike attachment guarantees the same degree of pressing and, consequently, the same depth of penetration of IR radiation into the sample. The obtained spectra can be used to estimate the content of comonomer units in the copolymer based on the Bouguer-Beer-Lambert law. Figure 1 shows the spectra of Cell-g-PMAA1, Cell-g-PMAA2, and the PMAA homopolymer. Using the corresponding option of the OPUS program built into the device, the integral intensities of the 1700 cm − 1 band (corresponding to the vibrations of COOH groups in PMAA) were calculated (the band at 1063 cm − 1 band, characterizing the vibrations of cellulose fragments, was too weak to be used for quantitative analysis). Assuming the PMAA content for the PMAA homopolymer to be 100%, the PMAA contents, f , for Cell-g-PMAA1 and Cell-g-PMAA2 were found to be 90 and 85 wt.%, respectively (Table 2 ). On the other hand, the f values may be calculated from Eq. (1), using M n values for PMAA side chains of Cell-g-PMAA1 and Cell-g-PMAA2 samples and average monomer unit molecular weights, \(\:\stackrel{-}{M}\left(MI\:unit\:cell\right),\) for the corresponding macroinitiators, Cell-BiB1 and Cell-BiB2 (Table 2 ), if an average number, z , of cellulose unites per one grafted PMAA side chain is known: $$\:f=\frac{{M}_{n}\left(PMAA\right)}{{M}_{n}\left(PMAA\right)+z\stackrel{-}{M}\left(MI\:unit\:cell\right)}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(1\right)$$ Since the f values for Cell-g-PMAA1 and Cell-g-PMAA2 are known from the quantitative analysis of IR spectra, the z values, characterizing the grafting density (Table 2 ), may be found from Eq. (2): $$\:z=\frac{{(1-f)M}_{n}\left(PMAA\right)}{f\stackrel{-}{M}\left(MI\:unit\:cell\right)}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(2\right)$$ Table 2 Compositions of polymer brushes Cell-g-PMAA1 and Cell-g-PMAA2. Sample M n (PMAA), Da \(\:\stackrel{-}{M}\left(MI\:unit\:cell\right),\) Da f z Cell-g-PMAA1 9700 222 0.90 4.8 Cell-g-PMAA2 11500 200 0.85 10.1 PMAA - - 1 - Photophysical properties of heteroligand complexes of Eu 3+ with Cell-g-PMAA copolymers in aqueous solutions The solutions obtained by mixing diluted aqueous solutions of EuCl 3 and the Cell-g-PMAA sample exhibit very weak luminescence due to low absorption; this is because the f–f transitions within individual ions are forbidden. Therefore, to obtain complexes of europium with carboxyl-containing copolymers that are capable of intense luminescence in aqueous solutions, we used the approach widely applied in lanthanide photophysics: the introduction of a sensitizer for the transfer of electron excitation energy to the radiating level of the lanthanide ion. As a sensitizer, phenanthroline (PHEN), one of the most effective sensitizers of europium luminescence, was used [ 13 – 14 ]. Its role is not limited to participation in the energy transfer process; it also displaces water molecules (which are effective luminescence quenchers) from the coordination sphere and modifies the coordination environment of the lanthanide ion. As a result of interaction with PHEN, the luminescence intensity of Eu 3+ solutions increases significantly. Figure 2 shows the excitation and phosphorescence spectra of Eu 3+ ions in complex with PHEN ([PHEN]/[Eu 3+ ] = 2) in solutions of Cell-g-PMAA2 molecular brush of varying concentrations and in the solution without the molecular brush (curve 3 ). The luminescence spectra contain bands, corresponding to 5 D 0 → 7 F j (j = 1–4) transitions for Eu 3+ ions. The maximum in the 585–600 nm region corresponds to the magnetic dipole transition. The most intense maximum in the 614–616 nm region corresponds to the 5 D 0 → 7 F 2 electric dipole transition. The weak maxima observed in the 653 nm and 680–710 nm regions are the 5 D 0 → 7 F 3 and 5 D 0 → 7 F 4 transitions, respectively [ 15 ]. It should be noted that curve 3 was obtained at an amplification factor of photodetector 100 times greater than that for curves 1 and 2 . Thus, for a correct comparison of the luminescence intensity, I lum , values shown in Fig. 2 , the I lum values for curve 3 should be divided by 100. In the absence of Cell-g-PMAA2, an aqueous solution of the Eu 3+ /PHEN complex of a similar concentration exhibits only very weak emission. At the same time, the luminescence of the heteroligand complex Eu 3+ /PHEN/Cell-g-PMAA2 exceeds the luminescence of the Eu 3+ /PHEN solution of the same concentration by more than 300 times. This dramatic increase in I lum indicates (a) the binding of Eu 3+ /PHEN by the Cell-g-PMAA2 molecular brush and the formation of a macromolecular coordination complex (polymer effect), (b) an efficient transfer of excitation energy from the triplet level of the phenanthroline ligand to the radiating level of Eu 3+ (antenna effect). For Cell-g-PMAA1 and Cell-g-PMAA2 samples 1 and 2 of Cell-g-PMAA molecular brushes in the concentration range from 0.02 to 0.2 mg/mL, positions of the maxima and shapes of the bands in the excitation and luminescence spectra do not depend on the concentration of the molecular brush, but the luminescence intensity I lum changes significantly. Figure 3 shows the dependence of I lum on the concentration of PMAA, expressed in moles of monomeric acid units, for Cell-g-PMAA1 and Cell-g-PMAA2. With an increase in the concentration of PMAA units in the solution from 10 − 4 to 10 − 3 mol/L, the value of I lum increases by more than 20 times. A further increase in the concentration of the copolymer leads to a decrease in luminescence due to concentration quenching [ 16 ]. The maximum I lum is observed at the ratio [COO – ]/[Eu 3+ /PHEN] = 12–13. Such a high ratio indicates that some of the PMAA units do not participate in the formation of the complex with Eu 3+ /PHEN due to steric restrictions caused by the polymeric nature of the ligand. For comparison, the dependence of I lum on the concentration of COO – units for linear PMAA is presented in Fig. 3 . It may be seen from Fig. 3 that the I lum values for Eu 3+ /PHEN complexes with Cell-g-PMAA1 and Cell-g-PMAA2 molecular brushes exceed the corresponding values for similar complexes with linear PMAA by more than an order of magnitude. This raises the question of how the topology of polymeric ligand affects the formation of the Eu 3+ /PHEN macromolecular complex with Cell-g-PMAA and photophysical properties of the product. In our opinion, this effect is related to the following factors: 1) Water is a selective solvent for Cell-g-PMAA, namely, a good solvent for ionized grafted PMAA chains [ 17 ] and a precipitant for the cellulose backbone. Under these conditions, a “core-shell” structure is formed in the brushes, in which the main rigid hydrophobic chain is surrounded by grafted hydrophilic chains of ionized PMAA. Such structures are capable of incorporating poorly water-soluble compounds into the hydrophobic region [ 10 , 11 ]. 2) Phenanthroline forms complexes with Eu 3+ that show more intense luminescence in nonpolar solvents compared to aqueous solutions. 3) The mobility of PMAA chain segments near the grafting point is inhibited compared to the mobility of PMAA segments distant from backbone [ 18 ], making the complex more rigid. Under these conditions, vibrations of OH groups of water molecules, causing strong luminescence quenching, become weaker [ 19 ]. The combination of these factors explains the observed increase in I lum values of Eu 3+ /PHEN in the presence of Cell-g-PMAA compared to the luminescence of the complex with linear PMAA. Apparently, due to solubilization of phenanthroline in the hydrophobic part of the brush (in the layer between the cellulose backbone and the grafted PMAA chains), the efficiency of binding between the polymer and Eu 3+ increases, which leads to displacement of luminescence-quenching water molecules from the inner coordination sphere of the metal ion (Fig. 4 ). In other words, in the vicinity of the main cellulose chain of the Cell-g-PMAA molecular brush (which is dissolved in water), certain “dry” zones are formed, in which the Eu 3+ /PHEN complex does not contain water molecules in the coordination sphere of the metal. In addition, reduction in the mobility of the segments of grafted chain localized near the backbone also suppresses non-radiative degradation of the excited states of the complex. The obtained results indicate the role of structural organization of a macromolecular ligand in the formation of europium ion complexes, which contributes to the enhancement of photoluminescence. Thus, amphiphilic brushes can be used not only as nanocontainers for poorly water-soluble substances, but also as nanoreactors in which heteroligand complexes are formed. A necessary condition for practical applications of lanthanide macromolecular complexes is their stability upon diluting their aqueous solutions (the absence of dissociation). It was shown above that in the concentration range of Cell-g-PMAA molecular brushes 0.02–0.2 mg/mL, the Eu 3+ /PHEN/Cell-g-PMAA complexes are stable, as indicated by the constancy of shape of the luminescence excitation spectra in the given concentration interval. At the concentration of Cell-g-PMAA equal to 0.003 mg/mL, the intensity of the band at 299 nm in the excitation spectra decreases, and a new band at 279 nm appears (Fig. 5 ). This is indicative of the appearance of a new emitting center due to the dissociation of the complex. In addition, with a decrease in the concentration of Cell-g-PMAA in the solution, the ratio of the intensities of the 615 and 590 nm bands (which characterize the symmetry of the europium ion environment) changes from 2.1 to 3.9, which also suggests a certain change in the composition of the inner coordination sphere of europium ion in the complex. An important photophysical characteristics of MCL, which is highly sensitive to any change in the composition of the inner coordination sphere, is the lifetime of the excited state of Eu 3+ in the complex, τ phosph . Constant values of τ phosph are usually considered as evidence of the constancy of composition and structure of a complex [ 20 ]. The τ phosph values for Eu 3+ in the complex were determined in solution from the kinetic curve of the phosphorescence intensity decay. Due to steric constraints caused by the polymeric nature of the ligand, metal complexes with different amounts of carboxyl groups are present in solution. Therefore, unlike the situation with low molecular weight complexes, the phosphorescence decay curves of macromolecular complexes are usually described by the following multi-exponential dependence: $$\:I={I}_{0}\left({A}_{i}{exp}(-t/{\tau\:}_{i})\right)\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(3\right)$$ where I 0 is the initial intensity; A i is the portion of intensity corresponding to the i -th emitting variant of a complex; t is the time elapsed since the moment of excitation; τ i is the lifetime of excited state of the i -th variant of a complex. The curves of phosphorescence intensity decay for the Eu 3+ /PHEN/Cell-g-PMAA and Eu 3+ /PHEN/PMAA complexes were described by a biexponential dependence. The obtained values of τ i and A i are given in Table 3 . The presence of two τ phosph values indicates that there are at least two types of emitting centers in the system, differing in the composition of the inner coordination sphere (both in the number of coordinated water and phenanthroline molecules and in the number of carboxyl groups) and testifies to the heterogeneous structure of the complexes. Higher values of τ 1 and τ 2 for the Eu 3+ /PHEN/Cell-g-PMAA complex compared to Eu 3+ /PHEN/PMAA are noteworthy. Most probably, this is due to the fact that the complex forms at the phase boundary in the “core-shell” structure, i.e., Cell-g-PMAA is both a nanocontainer for hydrophobic phenanthroline and a nanoreactor in which its complex with europium is formed. In the case of Eu 3+ /PHEN/PMAA, lower τ values are indicative of both the presence of complexes with a large number of water molecules (5–6) [ 21 ] and a less effecient role of the sensitizer due to weak binding of phenanthroline in aqueous solution. Table 3 Parameters describing the phosphorescence decay curves of Eu 3+ ions in the solution of Eu 3+ /PHEN/Cell-g-PMAA complexes in a biexponential representation. λ ex = 299 nm, [PHEN]/[Eu 3+ ] = 2. Polymer [Cell-g-PMAA], mg/mL A 1 τ 1 ,, µs A 2 τ 2 ,, µs Cell-g-PMAA1 0.09 0.65 333 0.35 863 Cell-g-PMAA2 0.09 0.65 333 0.35 901 PMAA 0.1 0.232 158 0.768 462 Interestingly, both Eu 3+ /PHEN/Cell-g-PMAA samples contain complexes with a phosphorescence lifetime τ phosph approaching 1 ms. It may be concluded that complete displacement of water molecules with phenanthroline molecules in the inner coordination sphere of the complex occurs, and a rigid environment around lanthanide ion is formed, in which the processes of non-radiative degradation of excited states are significantly hindered due to reduced mobility of the PMAA units adjacent to cellulose backbone [ 21 ]. Conclusion Amphiphilic molecular brushes Cell-g-PMAA were synthesized; the influence of structural organization (topology) of this macromolecular ligand on photophysical properties of europium complexes in dilute aqueous solutions was investigated. A comparison of photophysical properties of the Eu 3+ /PHEN/Cell-g-PMAA and Eu 3+ /PHEN/PMAA heteroligand complexes was carried out. It was revealed that the intensity of Eu 3+ luminescence in its complexes with Cell-g-PMAA exceeds the corresponding values for the complexes of Eu 3+ with linear PMAA by more than an order of magnitude. It is suggested that the Cell-g-PMAA copolymers serve not only as nanocontainers for hydrophobic phenanthroline molecules, but also as effective nanoreactors, in which the complex between Eu 3+ /PHEN and the PMAA units localized near the main hydrophobic cellulose backbone is formed. The formation of intensely luminescent complexes at the hydrophobic boundary occurs not only due to incorporation of phenanthroline molecules in the coordination sphere and substitution of water molecules with phenanthroline; in addition, the PMAA units located near the main chain (whose mobility is inhibited compared to the mobility of units remote from the main chain) are included in the complex with europium. The obtained results show the promise of Eu 3+ /PHEN/Cell-g-PMAA luminescent complexes as materials for photodynamic therapy; they may also be applied as probes or sensors for studying the mechanism of interaction between Cell-g-PMAA molecular brushes (used as carriers for hydrophobic anticancer drugs) and cells or tissues. Declarations Acknowledgements The work was carried out as a part of State Assignment № 1023031700043-2-1.4.4. Author contributions Elena L. Krasnopeeva: Investigation (lead). Tatiana N. Nekrasova: Investigation (supporting). Elena Yu. Melenevskaya: Investigation (supporting). Elena N. Vlasova: Investigation (supporting). Anna V. Kashina: Investigation (supporting). Michael A. Smirnov: Data curation (supporting); formal analysis (lead); writing – original draft (lead). Alexander V. Yakimansky: Data curation (lead); formal analysis (lead); resources (lead); supervision (lead); writing – review and editing (lead). Funding The National Research Center “Kurchatov Institute”, state assignment № 1023031700043-2-1.4.4. Data availability Data sharing does not apply to this article as no datasets were generated or analyzed during the current study. Conflict of interest The authors declare no conflicts of interest. References Bunzli J-CG (2014) Review: Lanthanide coordination chemistry: from concepts to coordination polymers. J Coord Chem 67:3706–3733. https://dx.doi.org/10.1080/00958972.2014.957201 Bunzli J-CG (2016) Lanthanide light for biology and medical diagnosis. 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Coord Chem Rev 295:1–45. https://doi.org/10.1016/j.ccr.2015.02.015 Guillet J (1985) Polymer photophysics and photochemistry: an introduction to the study of photoprocesses in macromolecules. Cambridge University Press, New-York Brandrup J, Immergut EH (1975) Polymer Handbook. Second Edition, Wiley Pautov VD, Nekrasova TN, Anan’eva TD, Meleshko TK, Ilgach DM, Yakimansky AV (2013) Intramolecular Mobility of Side Chains of Poly(methacrylic acid) in Regularly Grafted Copolyimides in Solution. Polym Sci Ser A 55:526–534. https://doi.org/10.1134/S0965545X13080051 Wang P, Ma JP, Dong YB (2009) Guest-Driven Luminescence: Lanthanide-Based Host–Guest Systems with Bimodal Emissive Properties Based on a Guest-Driven Approach. Chem Eur J 15:10432–10445. https://doi.org/10.1002/chem.200900435 Utochnikova VV (2019) The use of luminescent spectroscopy to obtain information about the composition and the structure of lanthanide coordination compounds. Coord Chem Rev 398:113006. https://doi.org/10.1016/j.ccr.2019.07.003 Arnaud N, Georges J (2003) Comprehensive study of the luminescent properties and lifetimes of Eu 3+ and Tb 3+ chelated with various ligands in aqueous solutions: influence of the synergic agent, the surfactant and the energy level of the ligand triplet. Spectrochim Acta Part A 59:1829–1840. https://doi.org/10.1016/S1386-1425(02)00414-6 Schemes Scheme 1 is available in the Supplementary Files section Supplementary Files GraphicalAbstract.docx Scheme1.docx SupportingInformation.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 04 May, 2026 Reviewers invited by journal 04 May, 2026 Editor invited by journal 29 Apr, 2026 Editor assigned by journal 27 Apr, 2026 First submitted to journal 23 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9513611","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":633821507,"identity":"562b8884-ed79-4106-a52a-3b55711f5c4d","order_by":0,"name":"Alexander V. Yakimansky","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5ElEQVRIiWNgGAWjYFACNoYDIEqCgfkAA2MDaVrYEojXwgDRwmNAnBaD48cSD92ouWMvOSPnm8TPHTZyDOyHj27Aq+VM2oHDOceeJc6WyN0m2XsmzZiBJy3tBl4tB9IbDuewHU6QA2qR4G07nNggwWOGX8v550At/w7by0nkPJP8S5SWG0CH5bYdZpwtkcMmTZQtkjeeJRzO7TucOLPnmbG1bFuaMRshv/CdTzP+nPPtsL3E8eSHN9+22cjxsx8+hleLwgEYSyCBRQJEs+FTDgLyDTAW/wHmD4RUj4JRMApGwcgEAN7kU8MpRBDMAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-8770-1453","institution":"Institute of Macromolecular Compounds: FGBUN Institut vysokomolekularnyh soedinenij Rossijskoj akademii nauk","correspondingAuthor":true,"prefix":"","firstName":"Alexander","middleName":"V.","lastName":"Yakimansky","suffix":""},{"id":633821508,"identity":"53283db5-93cc-4ef8-8e9c-eefc2de0f0b2","order_by":1,"name":"Elena L. Krasnopeeva","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Elena","middleName":"L.","lastName":"Krasnopeeva","suffix":""},{"id":633821509,"identity":"b5a7ad03-1b62-448d-899c-7d7606dc1cdc","order_by":2,"name":"Tatiana N. Nekrasova","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Tatiana","middleName":"N.","lastName":"Nekrasova","suffix":""},{"id":633821510,"identity":"d50fbe65-fc67-43db-ae58-c306bc13129d","order_by":3,"name":"Elena Yu. Melenevskaya","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Elena","middleName":"Yu.","lastName":"Melenevskaya","suffix":""},{"id":633821511,"identity":"6f405908-e885-423d-806b-b11b646f5080","order_by":4,"name":"Elena N. Vlasova","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Elena","middleName":"N.","lastName":"Vlasova","suffix":""},{"id":633821512,"identity":"252e1a84-ae35-4ddd-ad93-9872a3560351","order_by":5,"name":"Anna V. Kashina","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Anna","middleName":"V.","lastName":"Kashina","suffix":""},{"id":633821513,"identity":"48d3dc20-3133-43c5-804f-897e1300880e","order_by":6,"name":"Michael A. Smirnov","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Michael","middleName":"A.","lastName":"Smirnov","suffix":""}],"badges":[],"createdAt":"2026-04-24 07:16:44","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9513611/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9513611/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109068047,"identity":"a227c561-bf32-47af-816d-9c3eb3f6e36e","added_by":"auto","created_at":"2026-05-12 10:03:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":100310,"visible":true,"origin":"","legend":"\u003cp\u003eIR spectra of Cell-g-PMAA1 (curve \u003cem\u003e1\u003c/em\u003e), Cell-g-PMAA2 (curve \u003cem\u003e2\u003c/em\u003e), and PMAA homopolymer (curve \u003cem\u003e3\u003c/em\u003e).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/30b9c2c1c875039e47d9e6fb.png"},{"id":109016264,"identity":"a981a0f5-800d-42f8-80b0-4c0968487d9b","added_by":"auto","created_at":"2026-05-11 17:42:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":18795,"visible":true,"origin":"","legend":"\u003cp\u003eSpectra of luminescence excitation (emission wavelength λ\u003csub\u003eem \u003c/sub\u003e= 616 nm) and phosphorescence (excitation wavelength λ\u003csub\u003eex \u003c/sub\u003e= 299 nm) of Eu\u003csup\u003e3+\u003c/sup\u003e ions ([Eu\u003csup\u003e3+\u003c/sup\u003e] = 1×10\u003csup\u003e−4 \u003c/sup\u003eМ) in the complex with PHEN ([PHEN] = 2×10\u003csup\u003e−4 \u003c/sup\u003eМ) in solutions of Cell-g-PMAA2 of varying concentrations: \u003cem\u003eс\u003c/em\u003e = 0.12 mg/mL (curve \u003cem\u003e1\u003c/em\u003e), 0.09 mg/mL (curve \u003cem\u003e2\u003c/em\u003e), and 0 (curve \u003cem\u003e3\u003c/em\u003e).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/8b8cac4d2b8838f9022eab96.png"},{"id":109016261,"identity":"a26c23ec-876d-4d94-85e4-b623174e9ee3","added_by":"auto","created_at":"2026-05-11 17:42:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":19007,"visible":true,"origin":"","legend":"\u003cp\u003eDependence of I\u003csub\u003elum\u003c/sub\u003e of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN complexes in the solution of Cell-g-PMAA1 and Cell-g-PMAA2 molecular brushes, and linear PMAA on the concentration of PMAA units. The I\u003csub\u003elum\u003c/sub\u003e values for the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/PMAA complex were obtained at a higher amplification and should be divided by 2.5 for quantitative comparison with the data for Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA complexes.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/60801914a4cc25b5fa7298ed.png"},{"id":109016265,"identity":"37a166b5-cb61-4af8-971f-80eedf34a97e","added_by":"auto","created_at":"2026-05-11 17:42:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":63340,"visible":true,"origin":"","legend":"\u003cp\u003eProposed schematic structure of the (PHEN)\u003csub\u003e2\u003c/sub\u003e/Eu\u003csup\u003e3+\u003c/sup\u003e/Cell-g-PMAA macromolecular coordination complex.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/a8d5ca5fd63343bfd88e0222.png"},{"id":109081180,"identity":"6012c7fe-9547-44dd-95f3-f22c335edf82","added_by":"auto","created_at":"2026-05-12 12:04:11","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":16058,"visible":true,"origin":"","legend":"\u003cp\u003eExcitation and luminescence spectra of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA complexes at the concentrations of [Cell-g-PMAA] equal to 0.02 mg/mL (curves 1) and 0.003 mg/mL (curves 2).\u0026nbsp;\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/ca7f4bfc425d9449635165a8.png"},{"id":109082431,"identity":"fa18e266-c0fc-423d-86ad-0a956f9a1fff","added_by":"auto","created_at":"2026-05-12 12:39:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":504701,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/3768487b-fad6-4771-b1ac-83c93fcaeb53.pdf"},{"id":109016259,"identity":"40bc4fe8-cfe6-44ef-a73a-d21948bb3337","added_by":"auto","created_at":"2026-05-11 17:42:33","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":65172,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/583ff25eaafe4208fd9517eb.docx"},{"id":109016260,"identity":"6d14f398-b5ee-4c74-b93c-645f4d9d9721","added_by":"auto","created_at":"2026-05-11 17:42:33","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":78138,"visible":true,"origin":"","legend":"","description":"","filename":"Scheme1.docx","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/197b60580c6abbd8e8e10791.docx"},{"id":109016262,"identity":"67ff89c1-c2d0-4856-838d-3d8fa447852d","added_by":"auto","created_at":"2026-05-11 17:42:33","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":17479,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9513611/v1/0981cccea9bfc01562b7ec4c.docx"}],"financialInterests":"","formattedTitle":"An unexpected phenomenon of intense luminescence of aqueous solutions of macromolecular europium complexes","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAlong with the development of chemistry of low molecular weight coordination complexes of lanthanide ions, primarily Tb\u003csup\u003e3+\u003c/sup\u003e, Eu\u003csup\u003e3+\u003c/sup\u003e, Sm\u003csup\u003e3+\u003c/sup\u003e, Er\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e, which demonstrate luminescence in the visible and near-infrared spectral regions [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], the chemistry of macromolecular complexes of lanthanides (MCL) attracts attention of researchers. MCL retain the unique optical properties of lanthanide ions, such as quasi-monochromatic emission (their luminescence band width is equal to 5\u0026ndash;10 nm, while for organic chromophores it exceeds 100 nm), stability of emission over time (the absence of bleaching), and independence of the position of luminescence bands from the nature of a ligand and a solvent. In addition, they demonstrate large Stokes shifts, high values of excited state lifetimes, and independence of the shape of photoluminescence spectrum from the ligand nature for practically all lanthanides, with the exception of Eu\u003csup\u003e3+\u003c/sup\u003e ions, in whose spectra the Stark splitting of \u003cem\u003ef\u003c/em\u003e-levels is observed (caused by a change in the crystal field of a ligand). At the same time, compared to low molecular weight complexes of lanthanide ions, MCL have a number of advantages; for example, they can be used to obtain mechanically strong and stable materials in the form of films, gels, coatings, to prolong the action of drugs in the body, etc. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eVarying the structure of a macromolecular ligand not only provides means for targeted modification of luminescent properties of MCL, but also offers a number of additional possibilities. For example, the use of biologically active comonomers or comonomers containing covalently attached drugs makes it possible to visualize the interaction of complexes with cells and monitor their distribution in organs and tissues, to prolong the action of biosensors and probes, which allows for a reduction in the dose of the administered drug [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Lanthanide radioisotopes are also of interest for medicine [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In the last decade, luminescent lanthanide complexes have been actively studied as promising materials demonstrating a wide range of antitumor activity [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Ligands play an important role in the coordination of the properties of the respective complexes and are particularly significant for biological, biochemical, and medical applications [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Therefore, the synthesis of new low-toxicity, water-soluble ligands that form stable luminescent complexes with lanthanide ions is of fundamental and practical interest.\u003c/p\u003e \u003cp\u003eThe authors of [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] demonstrated the prospects and effectiveness of using amphiphilic brushes in photodynamic therapy; these brushes consisted of polyimide or cellulose backbones, to which poly(methacrylic acid) chains were regularly grafted. Such copolymers are capable of solubilizing (incorporating) large organic molecules and organometallic complexes in aqueous media and can serve as nanocontainers. Diphilic macromolecular brushes with a polyimide backbone and poly(methacrylic acid) blocks in side chains bind lanthanide ions [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Their luminescent complexes may be of interest for fluorescence diagnostics and photodynamic therapy.\u003c/p\u003e \u003cp\u003eIn this work, the amphiphilic cellulose-g-poly(methacrylic acid) (Cell-g-PMAA) brush was used as a macromolecular ligand to obtain luminescent complexes with Eu\u003csup\u003e3+\u003c/sup\u003e ions. The influence of ligand topology on photophysical properties of the complex in dilute aqueous solutions was investigated.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eMicrocrystalline cellulose (MCC) with an average particle size of 50 \u0026micro;m (degree of polymerization\u0026thinsp;~\u0026thinsp;330) was purchased from Acros Organics (Buchs SG, Switzerland). 2-Bromo-isobutyryl bromide (BiBB), 1-butyl-3-methylimidazolium chloride (BMIMCl) (ionic liquid), N,N-dimethylformamide (DMF) (solvent), pentamethyldiethylenetriamine (PMDETA), and \u003cem\u003etert\u003c/em\u003e-butyl methacrylate monomer (TBMA, 98%) were distilled twice under vacuum before use. Copper (I) bromide (CuBr) was purchased from Sigma Aldrich. Orthophosphoric acid (99%) used for acid hydrolysis was purchased from Saint-Louis, MS, USA. Trifluoroacetic acid, methylene chloride (reagent grade), tetrahydrofuran (THF) (chemically pure), ethyl alcohol, methyl alcohol, and potassium hydroxide were purchased from Vekton (Saint-Petersburg, Russia). Europium chloride hexahydrate (EuCl\u003csub\u003e3\u003c/sub\u003e\u0026times;6H\u003csub\u003e2\u003c/sub\u003eO) and 1,10-phenanthroline were purchased from Sigma Aldrich.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSynthetic Procedures\u003c/h3\u003e\n\u003cp\u003eThe synthesis of Cell-g-PMAA samples included three stages. Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e demonstrates the chemical route for preparation of this polymer brush.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the first stage, the macroinitiator Cell-BiB was prepared in ionic liquid (BMIMCl), and it was further used to polymerize \u003cem\u003etert\u003c/em\u003e-butylmethacrylate (TBMA) via ATRP mechanism, using CuBr/pentamethyldiethylenetriamine (PMDETA) catalytic system. Finally, thus prepared polymer brush Cell-g-PTBMA with cellulose backbone and poly(TBMA) side chains was subjected to acidic hydrolysis by CF3COOH in CH2Cl2, producing a water-soluble molecular brush Cell-g-PMAA with cellulose backbone and poly(methacrylic acid) side chains. The syntheses of the macroinitiator Cell-BiB, Cell-g-PTBMA and Cell-g-PMAA were carried out according to the method described in detail in [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] (see Supplementary material).\u003c/p\u003e\n\u003ch3\u003eDetermination of macroinitiator composition\u003c/h3\u003e\n\u003cp\u003eThe content of Br and C (ω(Br) and ω(C), in wt.% respectively) in macroinitiators was measured with energy dispersive X-ray (EDX) spectroscopy using a scanning electron microscope VEGA 3 SBH (Tescan, Czech Republic) equipped with an Aztec Energy X-act microanalysis system (Oxford Instruments, UK). The amount of isobutyroyl bromide per cellulose unit (n(BiB)/n(cell)\u0026thinsp;=\u0026thinsp;\u003cem\u003ex\u003c/em\u003e see Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) was calculated as:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:x=\\frac{\\text{n}\\left(\\text{B}\\text{i}\\text{B}\\right)}{\\text{n}\\left(\\text{C}\\text{e}\\text{l}\\text{l}\\right)}=\\frac{6\\:\\omega\\:\\left(Br\\right)}{79.9\\left(\\frac{\\omega\\:\\left(C\\right)}{12}-4\\frac{\\omega\\:\\left(Br\\right)}{79.9}\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003ePreparation of [Cell-g-PMAA]/[PHEN]/[Eu] solutions\u003c/h3\u003e\n\u003cp\u003eA weighed amount (10 mg) of Cell-g-PMAA was dissolved in 1 mL of 0.1N NaOH; after dissolution, 9 mL of distilled water was added. The initial solution was used to prepare a series of solutions with concentrations varying from 0.03 to 0.5 mmol (8 solutions). Then, 1 mL of Eu\u003csup\u003e3+\u003c/sup\u003e/phenanthroline (PHEN) solution was added to each sample, in which concentrations [Eu\u003csup\u003e3+\u003c/sup\u003e]\u0026thinsp;=\u0026thinsp;2\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mol/L, [PHEN]\u0026thinsp;=\u0026thinsp;4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mol/L. The solution was left to stay for 1 h, then the measurements were taken.\u003c/p\u003e\n\u003ch3\u003eIR spectroscopy\u003c/h3\u003e\n\u003cp\u003eThe IR spectra of samples were obtained at room temperature in the 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e wavenumber range (resolution: 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; number of scans: 30) using a \u0026ldquo;Vertex 70\u0026rdquo; FTIR spectrometer (Bruker, Ettlingen, Germany) equipped with a ZnSe attenuated total reflection (ATR) attachment (\u0026ldquo;Pike Technologies\u0026rdquo;, Madison, WI, USA). During the registration of the ATR spectra, a correction was made that took into account light penetration depth as a function of wavelength.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eGel permeation chromatography\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eDetermination of molecular weights of grafted PTBMA chains in Cell-g-PTBMA\u003c/h2\u003e \u003cp\u003eIn order to determine molecular weights of grafted PTBMA chains in Cell-g-PTBMA, these side chains were cleaved from the backbone by means of an alkaline hydrolysis as described in Supplementary materials.\u003c/p\u003e \u003cp\u003eThe cleaved PTBMA side chains were analyzed by size-exclusion liquid chromatography (SEC) using an Agilent-1260 Infinity chromatographic complex equipped with PLgel (7.5 \u0026times; 50 mm, 5 \u0026micro;m) guard column and two Agilent PLgel MIXED-C columns (7.5 \u0026sdot; 300 mm, 5 \u0026micro;m). THF was used as eluent at flow rate 1 ml/min (isocratic mode) and column temperature 40\u0026deg;C. Molecular weight characteristics were determined from refractometric detection data using calibration with PS standards. Chromatographic data were analyzed using Agilent GPC/SEC Software version 1.2.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\n\u003ch3\u003eLuminescence spectroscopy\u003c/h3\u003e\n\u003cp\u003eThe excitation and photoluminescence spectra of the solutions, as well as the kinetic phosphorescence decay curves, were recorded using an LS-100 spectrofluorometer (PTI, Canada). The excitation spectra of photoluminescence were recorded at an emission wavelength of λ\u003csub\u003eem\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;615 nm. The photoluminescence spectra were recorded at an excitation wavelength of 299 nm. The lifetime of the excited state of Eu\u003csup\u003e3+\u003c/sup\u003e in complexes (τ\u003csub\u003ephosph\u003c/sub\u003e) was determined from the kinetic phosphorescence decay curves. All measurements were performed in a quartz cuvette with an optical path length of 1 cm, in a thermostated cell at 25\u0026deg;C.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization of the synthesized Cell-g-PMAA copolymers\u003c/h2\u003e \u003cp\u003eTwo Cell-g-PMAA samples, Cell-g-PMAA1 and Cell-g-PMAA2, were prepared and characterized. They were obtained by acidic hydrolysis of side chains of Cell-g-PTBMA1 and Cell-g-PTBMA2 samples, respectively. In turn, Cell-g-PTBMA1 and Cell-g-PTBMA2 samples were synthesized by ATRP of TBMA on macroinitiators Cell-BiB1 and Cell-Bib2, differing in the weight fraction of Br. molar fraction \u003cem\u003ex\u003c/em\u003e of BiB-containing units (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAccording to EDX, the prepared macroinitiators Cell-BiB1 and Cell-Bib2 have 16 and 11 wt% Br, while carbon content was 46.9 and 50.2 wt.%, respectively. Calculations showed that sample \u003cb\u003e1\u003c/b\u003e has an average of 10 grafting points per 25 cellulose monomer units, while sample \u003cb\u003e2\u003c/b\u003e has 10 grafting points per 40 cellulose monomer units. From these data, molar fraction \u003cem\u003ex\u003c/em\u003e of BiB-containing units (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and average monomer unit molecular weights for macroinitiators Cell-BiB1 and Cell-Bib2 were found (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCompositions of macroinitiators Cell-BiB1 and Cell-Bib2.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003ex\u003c/em\u003e (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eaverage monomer unit molecular weight, Da\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCell-BiB1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0,40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e222\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCell-BiB2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0,24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe molecular weights, M\u003csub\u003en\u003c/sub\u003e, of grafted PTBMA chains in Cell-g-PTBMA polymer brushes, determined by GPC, were 16 and 19 kDa for samples Cell-g-PTBMA1 and Cell-g-PTBMA2, respectively, corresponding to M\u003csub\u003en\u003c/sub\u003e = 9,7 and 11,5 kDa for side PMAA chains of Cell-g-PMAA1 and Cell-g-PMAA2, respectively (degrees of polymerization\u0026thinsp;~\u0026thinsp;105 and ~\u0026thinsp;127, respectively).\u003c/p\u003e \u003cp\u003eThe Cell-g-PMAA1 and Cell-g-PMAA2 samples were further characterized by the wt. fraction of PMAA side chains, using their IR spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Pike attachment guarantees the same degree of pressing and, consequently, the same depth of penetration of IR radiation into the sample. The obtained spectra can be used to estimate the content of comonomer units in the copolymer based on the Bouguer-Beer-Lambert law. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the spectra of Cell-g-PMAA1, Cell-g-PMAA2, and the PMAA homopolymer. Using the corresponding option of the OPUS program built into the device, the integral intensities of the 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band (corresponding to the vibrations of COOH groups in PMAA) were calculated (the band at 1063 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band, characterizing the vibrations of cellulose fragments, was too weak to be used for quantitative analysis). Assuming the PMAA content for the PMAA homopolymer to be 100%, the PMAA contents, \u003cem\u003ef\u003c/em\u003e, for Cell-g-PMAA1 and Cell-g-PMAA2 were found to be 90 and 85 wt.%, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). On the other hand, the \u003cem\u003ef\u003c/em\u003e values may be calculated from Eq.\u0026nbsp;(1), using M\u003csub\u003en\u003c/sub\u003e values for PMAA side chains of Cell-g-PMAA1 and Cell-g-PMAA2 samples and average monomer unit molecular weights, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{M}\\left(MI\\:unit\\:cell\\right),\\)\u003c/span\u003e\u003c/span\u003e for the corresponding macroinitiators, Cell-BiB1 and Cell-BiB2 (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), if an average number, \u003cem\u003ez\u003c/em\u003e, of cellulose unites per one grafted PMAA side chain is known:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:f=\\frac{{M}_{n}\\left(PMAA\\right)}{{M}_{n}\\left(PMAA\\right)+z\\stackrel{-}{M}\\left(MI\\:unit\\:cell\\right)}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eSince the \u003cem\u003ef\u003c/em\u003e values for Cell-g-PMAA1 and Cell-g-PMAA2 are known from the quantitative analysis of IR spectra, the z values, characterizing the grafting density (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), may be found from Eq.\u0026nbsp;(2):\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:z=\\frac{{(1-f)M}_{n}\\left(PMAA\\right)}{f\\stackrel{-}{M}\\left(MI\\:unit\\:cell\\right)}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCompositions of polymer brushes Cell-g-PMAA1 and Cell-g-PMAA2.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003csub\u003en\u003c/sub\u003e(PMAA), \u003c/p\u003e \u003cp\u003eDa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{M}\\left(MI\\:unit\\:cell\\right),\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eDa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003ez\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCell-g-PMAA1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e222\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCell-g-PMAA2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePMAA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePhotophysical properties of heteroligand complexes of Eu\u003csup\u003e3+\u003c/sup\u003e with Cell-g-PMAA copolymers in aqueous solutions\u003c/h2\u003e \u003cp\u003eThe solutions obtained by mixing diluted aqueous solutions of EuCl\u003csub\u003e3\u003c/sub\u003e and the Cell-g-PMAA sample exhibit very weak luminescence due to low absorption; this is because the \u003cem\u003ef\u0026ndash;f\u003c/em\u003e transitions within individual ions are forbidden. Therefore, to obtain complexes of europium with carboxyl-containing copolymers that are capable of intense luminescence in aqueous solutions, we used the approach widely applied in lanthanide photophysics: the introduction of a sensitizer for the transfer of electron excitation energy to the radiating level of the lanthanide ion. As a sensitizer, phenanthroline (PHEN), one of the most effective sensitizers of europium luminescence, was used [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Its role is not limited to participation in the energy transfer process; it also displaces water molecules (which are effective luminescence quenchers) from the coordination sphere and modifies the coordination environment of the lanthanide ion.\u003c/p\u003e \u003cp\u003eAs a result of interaction with PHEN, the luminescence intensity of Eu\u003csup\u003e3+\u003c/sup\u003e solutions increases significantly.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the excitation and phosphorescence spectra of Eu\u003csup\u003e3+\u003c/sup\u003e ions in complex with PHEN ([PHEN]/[Eu\u003csup\u003e3+\u003c/sup\u003e]\u0026thinsp;=\u0026thinsp;2) in solutions of Cell-g-PMAA2 molecular brush of varying concentrations and in the solution without the molecular brush (curve \u003cem\u003e3\u003c/em\u003e). The luminescence spectra contain bands, corresponding to \u003csup\u003e5\u003c/sup\u003eD\u003csub\u003e0\u003c/sub\u003e \u0026rarr;\u003csup\u003e7\u003c/sup\u003eF\u003csub\u003ej\u003c/sub\u003e (j\u0026thinsp;=\u0026thinsp;1\u0026ndash;4) transitions for Eu\u003csup\u003e3+\u003c/sup\u003e ions. The maximum in the 585\u0026ndash;600 nm region corresponds to the magnetic dipole transition. The most intense maximum in the 614\u0026ndash;616 nm region corresponds to the \u003csup\u003e5\u003c/sup\u003eD\u003csub\u003e0\u003c/sub\u003e \u0026rarr;\u003csup\u003e7\u003c/sup\u003eF\u003csub\u003e2\u003c/sub\u003e electric dipole transition. The weak maxima observed in the 653 nm and 680\u0026ndash;710 nm regions are the \u003csup\u003e5\u003c/sup\u003eD\u003csub\u003e0\u003c/sub\u003e \u0026rarr;\u003csup\u003e7\u003c/sup\u003eF\u003csub\u003e3\u003c/sub\u003e and \u003csup\u003e5\u003c/sup\u003eD\u003csub\u003e0\u003c/sub\u003e \u0026rarr;\u003csup\u003e7\u003c/sup\u003eF\u003csub\u003e4\u003c/sub\u003e transitions, respectively [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt should be noted that curve \u003cem\u003e3\u003c/em\u003e was obtained at an amplification factor of photodetector 100 times greater than that for curves \u003cem\u003e1\u003c/em\u003e and \u003cem\u003e2\u003c/em\u003e. Thus, for a correct comparison of the luminescence intensity, I\u003csub\u003elum\u003c/sub\u003e, values shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the I\u003csub\u003elum\u003c/sub\u003e values for curve \u003cem\u003e3\u003c/em\u003e should be divided by 100.\u003c/p\u003e \u003cp\u003eIn the absence of Cell-g-PMAA2, an aqueous solution of the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN complex of a similar concentration exhibits only very weak emission. At the same time, the luminescence of the heteroligand complex Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA2 exceeds the luminescence of the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN solution of the same concentration by more than 300 times. This dramatic increase in I\u003csub\u003elum\u003c/sub\u003e indicates (a) the binding of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN by the Cell-g-PMAA2 molecular brush and the formation of a macromolecular coordination complex (polymer effect), (b) an efficient transfer of excitation energy from the triplet level of the phenanthroline ligand to the radiating level of Eu\u003csup\u003e3+\u003c/sup\u003e (antenna effect).\u003c/p\u003e \u003cp\u003eFor Cell-g-PMAA1 and Cell-g-PMAA2 samples \u003cb\u003e1\u003c/b\u003e and \u003cb\u003e2\u003c/b\u003e of Cell-g-PMAA molecular brushes in the concentration range from 0.02 to 0.2 mg/mL, positions of the maxima and shapes of the bands in the excitation and luminescence spectra do not depend on the concentration of the molecular brush, but the luminescence intensity I\u003csub\u003elum\u003c/sub\u003e changes significantly.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the dependence of I\u003csub\u003elum\u003c/sub\u003e on the concentration of PMAA, expressed in moles of monomeric acid units, for Cell-g-PMAA1 and Cell-g-PMAA2. With an increase in the concentration of PMAA units in the solution from 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e to 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mol/L, the value of I\u003csub\u003elum\u003c/sub\u003e increases by more than 20 times. A further increase in the concentration of the copolymer leads to a decrease in luminescence due to concentration quenching [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The maximum I\u003csub\u003elum\u003c/sub\u003e is observed at the ratio [COO\u003csup\u003e\u0026ndash;\u003c/sup\u003e]/[Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN]\u0026thinsp;=\u0026thinsp;12\u0026ndash;13. Such a high ratio indicates that some of the PMAA units do not participate in the formation of the complex with Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN due to steric restrictions caused by the polymeric nature of the ligand. For comparison, the dependence of I\u003csub\u003elum\u003c/sub\u003e on the concentration of COO\u003csup\u003e\u0026ndash;\u003c/sup\u003e units for linear PMAA is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt may be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e that the I\u003csub\u003elum\u003c/sub\u003e values for Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN complexes with Cell-g-PMAA1 and Cell-g-PMAA2 molecular brushes exceed the corresponding values for similar complexes with linear PMAA by more than an order of magnitude. This raises the question of how the topology of polymeric ligand affects the formation of the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN macromolecular complex with Cell-g-PMAA and photophysical properties of the product. In our opinion, this effect is related to the following factors:\u003c/p\u003e \u003cp\u003e1) Water is a selective solvent for Cell-g-PMAA, namely, a good solvent for ionized grafted PMAA chains [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and a precipitant for the cellulose backbone. Under these conditions, a \u0026ldquo;core-shell\u0026rdquo; structure is formed in the brushes, in which the main rigid hydrophobic chain is surrounded by grafted hydrophilic chains of ionized PMAA. Such structures are capable of incorporating poorly water-soluble compounds into the hydrophobic region [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e2) Phenanthroline forms complexes with Eu\u003csup\u003e3+\u003c/sup\u003e that show more intense luminescence in nonpolar solvents compared to aqueous solutions.\u003c/p\u003e \u003cp\u003e3) The mobility of PMAA chain segments near the grafting point is inhibited compared to the mobility of PMAA segments distant from backbone [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], making the complex more rigid. Under these conditions, vibrations of OH groups of water molecules, causing strong luminescence quenching, become weaker [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe combination of these factors explains the observed increase in I\u003csub\u003elum\u003c/sub\u003e values of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN in the presence of Cell-g-PMAA compared to the luminescence of the complex with linear PMAA. Apparently, due to solubilization of phenanthroline in the hydrophobic part of the brush (in the layer between the cellulose backbone and the grafted PMAA chains), the efficiency of binding between the polymer and Eu\u003csup\u003e3+\u003c/sup\u003e increases, which leads to displacement of luminescence-quenching water molecules from the inner coordination sphere of the metal ion (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn other words, in the vicinity of the main cellulose chain of the Cell-g-PMAA molecular brush (which is dissolved in water), certain \u0026ldquo;dry\u0026rdquo; zones are formed, in which the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN complex does not contain water molecules in the coordination sphere of the metal. In addition, reduction in the mobility of the segments of grafted chain localized near the backbone also suppresses non-radiative degradation of the excited states of the complex. The obtained results indicate the role of structural organization of a macromolecular ligand in the formation of europium ion complexes, which contributes to the enhancement of photoluminescence. Thus, amphiphilic brushes can be used not only as nanocontainers for poorly water-soluble substances, but also as nanoreactors in which heteroligand complexes are formed.\u003c/p\u003e \u003cp\u003eA necessary condition for practical applications of lanthanide macromolecular complexes is their stability upon diluting their aqueous solutions (the absence of dissociation). It was shown above that in the concentration range of Cell-g-PMAA molecular brushes 0.02\u0026ndash;0.2 mg/mL, the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA complexes are stable, as indicated by the constancy of shape of the luminescence excitation spectra in the given concentration interval. At the concentration of Cell-g-PMAA equal to 0.003 mg/mL, the intensity of the band at 299 nm in the excitation spectra decreases, and a new band at 279 nm appears (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This is indicative of the appearance of a new emitting center due to the dissociation of the complex. In addition, with a decrease in the concentration of Cell-g-PMAA in the solution, the ratio of the intensities of the 615 and 590 nm bands (which characterize the symmetry of the europium ion environment) changes from 2.1 to 3.9, which also suggests a certain change in the composition of the inner coordination sphere of europium ion in the complex.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAn important photophysical characteristics of MCL, which is highly sensitive to any change in the composition of the inner coordination sphere, is the lifetime of the excited state of Eu\u003csup\u003e3+\u003c/sup\u003e in the complex, τ\u003csub\u003ephosph\u003c/sub\u003e. Constant values of τ\u003csub\u003ephosph\u003c/sub\u003e are usually considered as evidence of the constancy of composition and structure of a complex [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe τ\u003csub\u003ephosph\u003c/sub\u003e values for Eu\u003csup\u003e3+\u003c/sup\u003e in the complex were determined in solution from the kinetic curve of the phosphorescence intensity decay. Due to steric constraints caused by the polymeric nature of the ligand, metal complexes with different amounts of carboxyl groups are present in solution. Therefore, unlike the situation with low molecular weight complexes, the phosphorescence decay curves of macromolecular complexes are usually described by the following multi-exponential dependence:\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:I={I}_{0}\\left({A}_{i}{exp}(-t/{\\tau\\:}_{i})\\right)\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(3\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eI\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e is the initial intensity; \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e is the portion of intensity corresponding to the \u003cem\u003ei\u003c/em\u003e-th emitting variant of a complex; \u003cem\u003et\u003c/em\u003e is the time elapsed since the moment of excitation; \u003cem\u003eτ\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e is the lifetime of excited state of the \u003cem\u003ei\u003c/em\u003e-th variant of a complex.\u003c/p\u003e \u003cp\u003eThe curves of phosphorescence intensity decay for the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA and Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/PMAA complexes were described by a biexponential dependence. The obtained values of \u003cem\u003eτ\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e are given in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The presence of two τ\u003csub\u003ephosph\u003c/sub\u003e values indicates that there are at least two types of emitting centers in the system, differing in the composition of the inner coordination sphere (both in the number of coordinated water and phenanthroline molecules and in the number of carboxyl groups) and testifies to the heterogeneous structure of the complexes. Higher values of τ\u003csub\u003e1\u003c/sub\u003e and τ\u003csub\u003e2\u003c/sub\u003e for the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA complex compared to Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/PMAA are noteworthy. Most probably, this is due to the fact that the complex forms at the phase boundary in the \u0026ldquo;core-shell\u0026rdquo; structure, i.e., Cell-g-PMAA is both a nanocontainer for hydrophobic phenanthroline and a nanoreactor in which its complex with europium is formed.\u003c/p\u003e \u003cp\u003eIn the case of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/PMAA, lower τ values are indicative of both the presence of complexes with a large number of water molecules (5\u0026ndash;6) [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] and a less effecient role of the sensitizer due to weak binding of phenanthroline in aqueous solution.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameters describing the phosphorescence decay curves of Eu\u003csup\u003e3+\u003c/sup\u003e ions in the solution of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA complexes in a biexponential representation. λ\u003csub\u003eex\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;299 nm, [PHEN]/[Eu\u003csup\u003e3+\u003c/sup\u003e]\u0026thinsp;=\u0026thinsp;2.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolymer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[Cell-g-PMAA], mg/mL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eτ\u003csub\u003e1\u003c/sub\u003e,, \u0026micro;s\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eτ\u003csub\u003e2\u003c/sub\u003e,, \u0026micro;s\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCell-g-PMAA1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e863\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCell-g-PMAA2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e901\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePMAA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.232\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e158\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.768\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e462\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eInterestingly, both Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA samples contain complexes with a phosphorescence lifetime τ\u003csub\u003ephosph\u003c/sub\u003e approaching 1 ms. It may be concluded that complete displacement of water molecules with phenanthroline molecules in the inner coordination sphere of the complex occurs, and a rigid environment around lanthanide ion is formed, in which the processes of non-radiative degradation of excited states are significantly hindered due to reduced mobility of the PMAA units adjacent to cellulose backbone [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eAmphiphilic molecular brushes Cell-g-PMAA were synthesized; the influence of structural organization (topology) of this macromolecular ligand on photophysical properties of europium complexes in dilute aqueous solutions was investigated. A comparison of photophysical properties of the Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA and Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/PMAA heteroligand complexes was carried out. It was revealed that the intensity of Eu\u003csup\u003e3+\u003c/sup\u003e luminescence in its complexes with Cell-g-PMAA exceeds the corresponding values for the complexes of Eu\u003csup\u003e3+\u003c/sup\u003e with linear PMAA by more than an order of magnitude. It is suggested that the Cell-g-PMAA copolymers serve not only as nanocontainers for hydrophobic phenanthroline molecules, but also as effective nanoreactors, in which the complex between Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN and the PMAA units localized near the main hydrophobic cellulose backbone is formed. The formation of intensely luminescent complexes at the hydrophobic boundary occurs not only due to incorporation of phenanthroline molecules in the coordination sphere and substitution of water molecules with phenanthroline; in addition, the PMAA units located near the main chain (whose mobility is inhibited compared to the mobility of units remote from the main chain) are included in the complex with europium.\u003c/p\u003e \u003cp\u003eThe obtained results show the promise of Eu\u003csup\u003e3+\u003c/sup\u003e/PHEN/Cell-g-PMAA luminescent complexes as materials for photodynamic therapy; they may also be applied as probes or sensors for studying the mechanism of interaction between Cell-g-PMAA molecular brushes (used as carriers for hydrophobic anticancer drugs) and cells or tissues.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe work was carried out as a part of State Assignment № 1023031700043-2-1.4.4.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eElena L. Krasnopeeva: Investigation (lead). Tatiana N. Nekrasova: Investigation (supporting). Elena Yu. Melenevskaya: Investigation (supporting). Elena N. Vlasova: Investigation (supporting). Anna V. Kashina: Investigation (supporting). Michael A. Smirnov: Data curation (supporting); formal analysis (lead); writing \u0026ndash; original draft (lead). Alexander V. Yakimansky: Data curation (lead); formal analysis (lead); resources (lead); supervision (lead); writing \u0026ndash; review and editing (lead).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe National Research Center \u0026ldquo;Kurchatov Institute\u0026rdquo;, state assignment № 1023031700043-2-1.4.4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData sharing does not apply to this article as no datasets were generated or analyzed during the current study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBunzli J-CG (2014) Review: Lanthanide coordination chemistry: from concepts to coordination polymers. 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Spectrochim Acta Part A 59:1829\u0026ndash;1840. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S1386-1425(02)00414-6\u003c/span\u003e\u003cspan address=\"10.1016/S1386-1425(02)00414-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Macromolecular ligands, Topology, Luminescence, Europium ions, Aqueous solutions","lastPublishedDoi":"10.21203/rs.3.rs-9513611/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9513611/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAmphiphilic cylindrical brushes consisting of a cellulose backbone and grafted poly(methacrylic acid) chains (Cell-g-PMAA) with high grafting density were synthesized. Their interaction with europium ions in dilute aqueous solutions (0.002\u0026ndash;0.02 wt%) was investigated. A comparative study of photophysical properties of (europium-phenanthroline) complexes with Cell-g-PMAA and (europium-phenanthroline) complexes with linear poly(methacrylic acid) was carried out. It was found that the intensity of Eu\u003csup\u003e3+\u003c/sup\u003e luminescence in the complexes with Cell-g-PMAA is an order of magnitude higher than the corresponding value for europium complexes with linear PMAA. It is suggested that solubilization of phenanthroline in the hydrophobic part of the brush (i.e., in the layer between the main chain and grafted chains) enhances its Eu\u003csup\u003e3+\u003c/sup\u003e binding efficiency, which, in turn, leads to the replacement of water molecules in the inner coordination sphere with phenanthroline molecules. In addition, the decrease in the mobility of grafted chain segments near the backbone \u0026ldquo;strengthens\u0026rdquo; the structure of the complex. The obtained results indicate that structural organization of a macromolecular ligand plays a significant role in the formation of europium ion complexes and contributes to the enhancement of photoluminescence.\u003c/p\u003e","manuscriptTitle":"An unexpected phenomenon of intense luminescence of aqueous solutions of macromolecular europium complexes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 17:42:28","doi":"10.21203/rs.3.rs-9513611/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-05-04T17:03:55+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-04T04:18:31+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2026-04-29T07:25:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-28T03:21:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2026-04-24T03:16:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"920356bf-6040-41a4-aa91-b2fed7c22bf5","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"","date":"2026-05-04T17:03:55+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-04T04:18:31+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T17:42:28+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 17:42:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9513611","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9513611","identity":"rs-9513611","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}