TY - JOUR
T1 - Tuning and reviving the luminescence of a new class of pyridyl β-diketonate Eu(III) metallomesogens
T2 - From molecules to entrapment in polymer particles
AU - González-Tobío, Brais
AU - Duarte, Frederico
AU - Arribas-Delgado, Andrés
AU - Fernández-Lodeiro, Carlos
AU - Fernández-Lodeiro, Javier
AU - Cano, Mercedes
AU - Lodeiro, Carlos
AU - Cuerva, Cristián
N1 - Funding Information:
info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UID%2FQUI%2F50006%2F2013/PT#
info:eu-repo/grantAgreement/FCT/OE/2021.05161.BD/PT#
A solution of the corresponding Eu(III) compound (1 mg), and PMMA (100 mg) was prepared in 12 mL of chloroform, and added into a PFA support (Bohlender, Gmbh, Germany). Thin films were obtained after slow solvent evaporation at room temperature for 24 h in the dark.All the Eu(III) compounds were structurally characterised by FTIR, 1H NMR, CHN elemental analysis, and mass spectrometry (see experimental section for details). The FTIR spectra show the characteristic signals of the β-diketonate ligands, the ν(C–H)aliph, ν(C[dbnd]C) + ν(C[dbnd]O) and δ(C–H)py being remarkable at 2920–2850, 1592–1550 and 776 cm−1, respectively (Figs. S1–S4). For both type of compounds (EuL2N and EuL4N), it is interesting to note that the ν(C[dbnd]O) value (ca. 1594 cm−1) appears close to the corresponding free ligand (ca. 1600 cm−1). This fact was previously found for compounds bearing pyridyl β-diketone ligands with the N atom at the 2 position of the pyridine moiety, which were coordinated in a bidentate fashion via N,O to the metal centre [34]. A similar situation is considered for 2. By contrast, for the series of compounds 1a-c, the position of the pyridyl nitrogen atom prevent the N,O coordination. In both cases, the β-diketonate ligands are acting as anionic ones, having the negative charge localised on the free oxygen atom of the diketonate ligands (for EuL2N compounds), but delocalised for the related EuL4N derivatives, so supporting the formulation proposed for these Eu(III) species. The similar value of the ν(C[dbnd]O) observed for both type of compounds (1a-c and 2) respect to that found for the corresponding free ligands can be understood by considering the high negative charge density located at the oxygen atom of the diketonate group that is not involved in the coordination (for compound 2), as well as at the pyridyl nitrogen atom at 4-position (for compounds 1a-c). This fact also suggests the establishment of potential interactions with other Eu(III) metal centres to form polynuclear species, most likely counteracting the decrease of the ν(C[dbnd]O) value expected by the coordination effect.In the present work, we demonstrated that ligands of the type pyridine-functionalised β-diketone with the nitrogen atom at the 2 or 4 position of the pyridine ring, can be coordinated to the Eu(III) centre in a NO or OO bidentate fashion, respectively, giving rise to polynuclear compounds containing a Eu2/L5 metal-to-ligand ratio. The species with the ligands coordinated via OO and bearing 12 and 14 carbon atoms at the alkyl chains behave as liquid crystals, exhibiting SmA mesophases. All the compounds show luminescence properties as a result of the antenna effect of the coordinated β-diketonate ligands. By using the Eu(III) compounds as dopants, polymer thin films and colloidal dispersions of microparticles were prepared, and their photophysical behaviour studied. Protonation of the pyridine moiety causes a drastic change in the emission of the polymer supports due to blocking of the energy transfer process from the antenna ligands to the Eu(III) centre. This behaviour is fully reversible in presence of ammonia solution, so that the new polymer materials can be used as sensors of acid media. At the nanoscale, the polymer particles encapsulating the Eu(III) compounds act as a barrier that avoids direct contact of the compounds with the aqueous medium. As a consequence, the typical quenching effect by water coordination does not occur, and the Eu(III) compounds maintain their red emission in presence of water. Thus, oil-in-water droplets can be an effective method to revive the luminescence emission of Eu(III) compounds in water, which may have a great relevance in biomedical or biological applications.This work was partially supported by the Proteomass Scientific Society, grant 2021.C.C. thanks the Spanish Foundation Alfonso Martín Escudero for his postdoctoral fellowship in 2019–2020. F.D. thanks the FCT/MEC for the summer school grant allocated to the LAQV/REQUIMTE. J.F.L. thanks to FCT/MEC and FCT-UNL for the research contract under the DL57 program. C.F.L. acknowledges Xunta de Galicia for a predoctoral scholarship (Programa de axudas á etapa predoutoral) (Galicia-Spain).
Publisher Copyright:
© 2022 Elsevier Ltd
PY - 2022/8
Y1 - 2022/8
N2 - A new class of polynuclear Eu(III) compounds bearing pyridyl β-diketonate ligands have been synthesised, and their thermal and photophysical behaviour studied. Since they behave as highly emissive materials, polymer thin films were prepared by using the Eu(III) compounds as a dopant and poly(methyl methacrylate) as the matrix. Interestingly, the luminescence properties of the new materials can be tuned by protonation of the nitrogen atom at the pyridine moiety of the ligands, which allows controlling the energy transfer between the antenna ligands and the Eu(III) centre. This stimuli-responsive luminescence behaviour causes a drastic colour change from red to green that can be useful to detect highly acidic media. The antenna effect has been also explored at the nanoscale. Several colloidal dispersions of poly(methyl methacrylate) microparticles encapsulating the luminescent Eu(III) compounds have been obtained from oil-in-water droplets. The polymer matrix acts as a barrier and protects the coordination environment of the Eu(III) compounds, avoiding the quenching effect by water coordination. This method of entrapment can constitute a powerful tool to revive the luminescence of Eu(III) species in aqueous media.
AB - A new class of polynuclear Eu(III) compounds bearing pyridyl β-diketonate ligands have been synthesised, and their thermal and photophysical behaviour studied. Since they behave as highly emissive materials, polymer thin films were prepared by using the Eu(III) compounds as a dopant and poly(methyl methacrylate) as the matrix. Interestingly, the luminescence properties of the new materials can be tuned by protonation of the nitrogen atom at the pyridine moiety of the ligands, which allows controlling the energy transfer between the antenna ligands and the Eu(III) centre. This stimuli-responsive luminescence behaviour causes a drastic colour change from red to green that can be useful to detect highly acidic media. The antenna effect has been also explored at the nanoscale. Several colloidal dispersions of poly(methyl methacrylate) microparticles encapsulating the luminescent Eu(III) compounds have been obtained from oil-in-water droplets. The polymer matrix acts as a barrier and protects the coordination environment of the Eu(III) compounds, avoiding the quenching effect by water coordination. This method of entrapment can constitute a powerful tool to revive the luminescence of Eu(III) species in aqueous media.
KW - Antenna effect
KW - Lanthanide complexes
KW - Luminescence
KW - Metallomesogens
KW - Polymer particles
UR - http://www.scopus.com/inward/record.url?scp=85130817901&partnerID=8YFLogxK
U2 - 10.1016/j.dyepig.2022.110440
DO - 10.1016/j.dyepig.2022.110440
M3 - Article
AN - SCOPUS:85130817901
SN - 0143-7208
VL - 204
JO - Dyes and Pigments
JF - Dyes and Pigments
M1 - 110440
ER -