Dynamics of proton, charge & energy transfers in solutions and within metal-organic frameworks: toward sensing and nanophotonic applications
- Autores: Mario Gutiérrez Tovar
- Directores de la Tesis: Abderrazzak Douhal (dir. tes.)
- Lectura: En la Universidad de Castilla-La Mancha ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Hermenegildo García Gómez (presid.), Boyko Yuda Koen (secret.), Robert Pansu (voc.)
- Materias:
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- Resumen
In this Ph.D. thesis, I have investigated the spectroscopic and photodynamical properties of different molecular systems as well as a series of nanomaterials known as “Metal-Organic Frameworks” (MOFs). I explored in “real time” the photophysical and photochemical processes that take place in the excited state of these systems and I also determined how the environment or different structural changes affect these excited state processes. A brief summary of the obtained results is shown below: 1) The spectroscopic and photophysical properties of (2´-hydroxyphenyl)benzoxazole (HBO) and two amino-derivatives (5A-HBO and 6A-HBO) have been investigated. The presence of the electron-donor group in 5A-HBO and 6A-HBO produces an increment in the electron density of the molecule owing to a photoinduced intramolecular charge transfer (ICT) process. This provokes a decrease in the acidity of -OH group at the electronically first excited state (S1), and thus, the ESIPT process is slowing down. The position of the (-NH2) group in the molecular frame also influences the photoacid properties of the -OH group. When the (-NH2) group is in the 5-position, the -OH group is less photoacid than when the (-NH2) is in the 6-position, and thus, the ESIPT is faster for the latter molecule than for the former. Moreover, the environment, in this case the basicity of the solvents, influences the ESIPT process. For example, in slightly basic solvents (ACN or THF), the ESIPT is not taking place for 5A-HBO, while for 6A-HBO it is occurring in a reversible way. In a less basic solvent (DCM), the ESIPT is reversible for 5A-HBO and irreversible for 6A-HBO.
2) The spectroscopic and photodynamical properties of a series of Zr-based MOFs (Zr-NDC, Zr-NADC (2-35%), Zr-NDC/Tz and Zr-NDC/CN) and their interaction with different molecules were also explored. We have observed the emission of monomers and excimers of naphthalene linkers in Zr-NDC MOF. When part of the naphthalene linkers are functionalized with amino-groups (Zr-NADC) an energy transfer from the excited naphthalene linkers to the amino-functionalized ones are shown. Both MOFs (Zr-NDC and Zr-NADC) exhibits also an ultrafast Ligand-to-Cluster Charge Transfer with the subsequent generation of a long-lived charge-separated state. The generation of this state is fundamental to use these materials as photocatalysts.
Taking advantage of the porous structure of Zr-NDC MOF, different organic fluorescent molecules have been entrapped into those pores. By using energy transfer processes from MOF to the encapsulated dyes, we fabricated hybrid materials that emit cool white light with a high quantum yield. As a final goal to fabricate a MOF-LED, the first step was getting and studying a homogenous film. To this end, Zr-NDC and C153@Zr-NDC MOF materials were dispersed in polycarbonate (PC) films. The NDC excimer formation in Zr-NDC as well as the energy transfer from MOF to C153 in C153@Zr-NDC were observed when both materials are embedded in PC films. With this in mind, we fabricated the first Zr-MOF-LEDs and investigated their electroluminescence properties. In this way, we demonstrated that both, the dye encapsulation and the presence of defect in the MOF structure have considerable influence in the device performance.
Finally, we also explored the spectroscopic and photodynamical properties of new functionalized Zr-NDC/Tz and Zr-NDC/CN MOFs, and how the presence of different nitroaromatic explosive molecules affect them. The presence of small amounts of trinitrophenol produces large quenching of their emission intensity. This quenching is favoured owing to specific interactions (H-bonds) between the Tz and CN groups of the MOFs and the -OH of the TNP molecule.
All these photophysical studies are keystones for further improvements of this kind of nanomaterials to use in different fields as photocatalysts, fluorescent sensors or optoelectronic devices.
