Materials 2D luminescents per tintes intel·ligents

Treballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2021, Tutora: E. Carolina Sañudo ZotesThe increment of documents or currency counterfeiting is being a problem for society, making it necessary to find a solution. One possible method is the development of smart inks, which are luminescent under certain light wavelength. To do it, metal-organic frameworks (MOFs) with structure [Ln(CH3COO)(PhCOO)2] of Ln = Tb, Eu and Sm are used. Homometallic and heterometallic compounds are synthetized with Ln:Ln’ proportions of approximately 0,5:0,5, 0,25:0,75 and 0,75:0,25. All of them are luminescent under UV light: Tb is green, Eu red and Sm violet. Due to the great properties of 2D materials, such as graphene, exfoliations of homometallic MOFs are carried out to achieve single-layer compounds dispersed in i-propanol. Both for MOFs and for exfoliations, a luminescence study has been done to see where the electronic transitions responsible of their colour appear. Although f-f transitions are prohibited, due to the antenna effect of the ligand, the expected electronic transitions of Lanthanides can be observed in all compounds. Furthermore, Tb in heterometallic compounds acts as sensitizer, making the emission of the partner Ln’ more intense. After the confirmation of exfoliations luminescence, they are stamped. In a preliminary study, it is observed that through the fluorimeter the corresponding electronic transition appears, but it is not possible to see its luminescence at naked eye under UV light

Luminiscent and Magnetic Tb-MOF Flakes Deposited on Silica

The synthesis of a terbium-based 2D metal-organic framework (MOF), of formula [Tb(MeCOO)(PhCOO)2] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of tlf ⇡ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications

Luminescent and magnetic [TbEu] 2D metal-organic frameworks

We present the synthesis, through a simple, microwave-assisted method, of lanthanoid-based 2D metal–organic frameworks (MOFs) of general formula [LnxLn′1−x(MeCOO)(PhCOO)2], including homonuclear compounds (x = 1), Ln[double bond, length as m-dash]Eu, Tb, and heterometallic compounds, [TbEu]. The crystalline material is formed by neutral nanosheets held together by van der Waals interactions, which can be easily exfoliated by sonication. Photoluminescent emission in the visible range was observed for all of the synthesized 2D MOF compounds via excitation of the ligand, showing benzoates are efficient antenna ligands. Efficient energy transfer from Tb → Eu was observed in the heterometallic [TbEu] compounds, which could potentially perform as luminescent thermometers. Inks containing nanosheets of 2D MOFs exfoliated in solution were prepared, and luminescent prints of Tb and Eu 2D MOFs on paper were made to show the possible application for anticounterfeiting. Frequency-dependent ac susceptibility results show the occurrence of slow magnetic relaxation in [TbEu] compounds through direct relaxation mechanisms, affected by bottleneck effect. A slowing down of the relaxation time is observed as the Eu/Tb ratio increases.E. C. S. acknowledges financial support from the Spanish Government Ministerio de Ciencia Innovación y Universidades (project PGC2018-098630-B-I00). E. B. and A. A. acknowledge financial support from the Gobierno de Aragón (RASMIA group E12-23R). This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231.Peer reviewe

Luminescent and magnetic Tb-MOF flakes deposited on silicon

This article belongs to the Special Issue 2D Magnetic Molecular Materials.The synthesis of a terbium-based 2D metal–organic framework (MOF), of formula [Tb(MeCOO)(PhCOO)2] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of τlf ≈ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications.This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant Nos. MAT2017-83468-R; PGC2018-098630-B-I00 (ECS)) and from the regional Government of Aragon (E12-20R RASMIA project).Peer reviewe