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Luminescent Metal Organic Frameworks for anti-counterfeiting and logic computing

Periodic Reporting for period 1 - LUMIMOF (Luminescent Metal Organic Frameworks for anti-counterfeiting and logic computing)

Reporting period: 2021-04-01 to 2023-03-31

First of all, I would like to point out that the LUMIMOF project was designed to carry them out for 2 years. However, the project only lasted 5 months because I got a position as Assistant Professor at another University. Due to this fact, it has not been possible to carry out all the objectives of the project.

Data security has become an important issue for both government offices and companies. The counterfeiting of valuable documents, products, or currency is a global problem that challenges industry, governments and customers. Accordingly, counterfeiting in the medical sector can severely jeopardize human health while the counterfeiting of documents is an infringement of copyright laws.
On the other hand, information technology (IT) has advanced significantly since the first programmable computer was invented. Computers have become smaller, smarter and more efficient due to the downscaling of silicon-based computer components. However, the top-down miniaturization of silicon-based components is fast reaching its limitations due to physical constraints and economical non-feasibility. In order to avoid these limits, molecular computing could be an alternative to conventional silicon-based computing. In recent decades, molecular logics based on chemical inputs and measurable optical outputs have received significant attention. Various simple logic gates and multilevel networks are constructed by employing organic molecules, polymers, and biomolecules. Some of these building molecules generate an input signal by means of their luminescent properties. Among these molecules, DNA molecules are the most widely reported luminescent logic gates due to their conformational polymorphism, molecular recognition and sequence-controlled functional features. Nevertheless, they have some intrinsic limitations: i)uncertain DNA amplification efficiency leads to low sensitivity and accuracy for the input signals; ii) the luminescence signals of DNA-based outputs are unstable; and iii) gate miscommunication increases in DNA-based logic circuits as the molecules diffuse freely in solution. Considering these drawbacks, novel luminescent materials, which can recognize certain analytes in a system are required and constructed for advanced logic gates.
In this context, lanthanide-based metalorganic frameworks (LnMOFs) have attracted great attention due to the fact that lanthanide ions are widely recognized for their exceptional luminescence. Compared to other luminescent materials, such as organic molecules (DNA) or inorganic solids (oxide nanoparticles), LnMOFs present several advantages : i) a versatile composition, allowing for almost infinite combinations; ii) large channels and pores where a guest can be introduced; iii) inorganic cluster (lanthanide ions), organic ligands (the π electrons in the ligands) and adsorbed guest molecules may be optically active, enabling a wide range of emissive phenomena; and iv) the modification of their luminescence properties through the simple change or functionalization of the organic linker; the Ln3+ species or the guest molecules provide an easy methodology to synthesize interesting luminescent materials. These features make them excellent candidates for both anti-counterfeiting and logic computing applications. Therefore, the objective of LUMIMOF project is to develop LnMOF nanoparticles (nano-LnMOFs) able to be used in anti-counterfeiting and logic computing applications through printing techniques.

LUMIMOF project comprised four main scientific objectives 1)To rationally synthesize robust nano-LnMOFs through different methodologies; 2) To study their luminescent properties; 3) To develop tailored printing techniques for the most promising MOFs; and 4) To evaluate the nano-LnMOFs printed as anti-counterfeiting materials and molecular computing devices.
Nevertheless, I only could carry out the first and second objective
LnMOFs have received attention due to their rich coordination characteristics, high stability and exceptional luminescence properties arising from 4f electrons. Several LnMOF structures have been reported through a judicious selection of organic ligands and metal ions. However, the LnMOF materials used are mostly single-crystals or micrometer scale powders. Therefore, the first stage of this proposal is the synthesis of robust nano-LnMOFs. To obtain the desired materials, we designed two strategies:
Stage 1a. Synthesis and characterization of Eu(BTC) and Tb(BTC) at nanometer scale
According to the literature, we have selected two LnMOFs with high stability and excellent luminescence properties: Eu(BTC) (BTC = benzene-1,3,5-tricarboxylate) and Tb(BTC). As is well known, Eu3+ and Tb3+ have an exceptional luminescence.
These solids were synthesized according to previously described methods. However, the synthetic conditions were adapted to yield nanosized materials. Synthetic conditions are a key element in obtaining nano size materials. We obtained nano Tb(BTC) particles with homogeneous size by adding modulating substances (Figure 1). Concretely, we added sodium acetate as surfactant. However, we were not able to obtain nanoparticle of Eu(BTC) material. We tried with different synthesis conditions adjusting i) temperature; ii) pressure; iii) reaction time; iv) microwave or solvothermal synthesis; and by v) adding different surfactants but we only obtained microcrystals (Figure 1).
The synthesized nano-Tb(BTC) material was fully characterized through different techniques (Figure 2): X-ray powder diffraction (XRPD) to assess the crystalline structure and particle size, N2 isotherm adsorption to characterize the porosity and thermal stability studies
Stage 1b. Post-synthetic modification of robust and porous nano-MOFs in order to incorporate Ln3+. Due to the termination of project we were not able to complete this stage.

The last stage carried out of the project was:
Study of nano-LnMOF luminescence properties in order to assess their potential in logic gates and anti-counterfeiting applications.
We have studied the emission and excitation spectra of nano-Tb(BTC) material and micro-Tb(BTC) materias and the emission decay dynamics (Figure 3).The results shows the nano-Tb(BTC) has the higher luminescence lifetime. A high lifetime is important for integrating nano-LnMOFs in different substrates.
Finally, we have measured the emission quantum yield. Both materials present similar quantum yield.

Finally I would like to emphasize that due to the termination of the project it has not been possible project exploitation and dissemination
Taking into account that I was working for 5 months, it is difficult to comment the societal implications that this project will have.

However, some interesting results have been obtained:

We have synthesized a material at nanometer scale with high luminescence lifetime and good quantum yield.
Therefore, the material

These results indicate that nano-Tb(BTC) is an optimal candidate to be used as a novel luminescent material for several applications. This material could be used to recognize certain analytes in a system and build advanced logic gates. In addition, nano-Tb(BTC) has potential applications to solve society's problems such as counterfeiting due to the excellent luminescent properties that it presents at nanometer particle size.
SEM images of a) nano-Tb(BTC) material; b) micro-Eu(BTC) material
a) Excitation and emission spectra, and emission decay dynamics for nano-Tb(BTC); b) Excitation and
a) PXRD patterns of micro-Tb(BTC) and nano-Tb(BTC); b) TGA analysis for nano-Tb(BTC); c) N2 isotherm