Design and synthesis of organic-inorganic hybrid materials exhibiting optical and luminescent properties in the solid state
- Autores: Laura Jiménez García-Patron
- Directores de la Tesis: Ernesto Brunet Romero (dir. tes.)
- Lectura: En la Universidad Autónoma de Madrid ( España ) en 2012
- Idioma: español
- Tribunal Calificador de la Tesis: Carmen Carreño García (presid.), Bernardo Herradón García (secret.), Claude Forano (voc.), Muller Gilles (voc.), Aurelio Cabeza Díaz (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: digitool-uam.greendata.es
- Resumen
Design and synthesis of organic¿inorganic hybrid materials exhibiting optical and luminescent properties in the solid state Our modern society is mainly characterized by the use of new technologies. There is no new technology without the discovery of new materials. The design of porous solids, based in supramolecular structures, with properties that change when their wide enough cavities are accessed by external molecular species, is a challenge of great scientific and technological importance. Unfortunately, in the majority of cases the predictive knowledge of the structures or even the chemical composition of the solid materials is still a chimera. In contrast, the art or science of designing and synthesizing organic molecules has reached very high levels of sophistication, based upon a relatively simple set of rules that guide both the invention and synthesis of new compounds. As organic chemists confronted to the task of building new solid structures with tailored chemical properties, we do inevitably need to develop some rational approach and to establish the corresponding set of rules allowing for a realistic level of predictive knowledge in the construction of solid scaffolds.
We found these conditions reasonably accomplished by the use of layered salts of tetravalent transition metals, namely zirconium phosphate, which are very versatile materials whose handling complies with what we have termed rational synthetic method, i.e. the development of a set of relatively simple rules that confers sufficient predictive knowledge to the building of crystalline materials. The synthetic rationale elaborated by us through a number of years is modular because it comprises the design and synthesis of appropriate organic molecules in one hand and on the other, their stepwise introduction into the inorganic framework. Specifically and directed to this aim, the ¿¿phase of zirconium phosphate (¿¿ZrP from now on) has been widely studied due to its thermal and chemical stability, its versatility and its unique property of replacing the superficial phosphates by phosphonates without affecting the integrity and rigidity of the inorganic layers. Furthermore, the structure of the lamellae of ¿¿ZrP is intrinsically dissymmetric as the internal phosphates bonded to four different Zr atoms are thus stereogenic centers.
Results of our research group concerning the chemistry of metal phosphates/phosphonates in relation with recognition, chemically¿driven porosity changes, chiral memory and supramolecular chirality, luminescence signaling, photoinduced electron¿transfer, gas storage and drug confinement, led us to propose the following objectives for the development of this doctoral thesis: ¿ The design of supramolecular solid systems based on ¿¿ZrP which are capable of triggering efficient luminescence processes in order to perform the study of their photophysical properties in the solid state. Furthermore, due to the lack of a reliable methodology for quantifying the luminescence response, a protocol for determining the quantum yields in this kind of materials would be developed.
¿ The design and synthesis of novel intrinsically¿chiral materials based on ¿¿ZrP which would give rise to the emission of polarized luminescence. Therefore, we shall perform the study of their chiroptical properties concerning Circularly Polarized Luminescence (CPL) measurements in the solid state. There are very few precedents of that accomplishment in the literature.
In particular, this work requires the fulfillment of the following steps: ¿ Preparation and screening of the organic diphosphonates based on a library of chromophores derived from bis¿heterocyclic pyridines.
¿ Previous photophysical study in solution of the lanthanide complexes of the synthesized organic chromophores. It will be carried out by UV¿Visible absorption, fluorescence and luminescence measurements. In the case of the chiral chromophores, CD (Circular Dichroism) and CPL measurements in solution will be also performed.
¿ Topotactic exchange of the synthesized diphosphonates within the inorganic matrix of ¿¿ZrP and characterization of the resultant porous hybrid materials.
¿ Intercalation reactions of appropriate lanthanide salt in the porous hybrid materials to form the light¿emitting matrices and characterization of the new materials.
¿ Photophysical study of the synthesized porous hybrid materials accomplished by diffuse reflectance, fluorescence, steady¿state and time¿resolved luminescence.
CPL measurements of the intrinsically chiral materials in the solid¿state will be also performed.
These objectives have led to the following accomplishments: In a first stage of the research, materials based on ¿¿ZrP were designed and prepared containing appropriate species with chromophores able to efficiently sensitize lanthanide ions and thus induced their emission.
¿ To that effect we have synthesized phosphonates derived from the chromophoric units of bis¿triazolylpyridine, bispyrazolylpyridine and terpyridine (Figure 1), and attempted their introduction within the inorganic matrix at different exchange levels.
N N N N N N N P P OH HO O O HO OH 1 2 N P N N N N O HO HO O O HO HO 3 N N N O P OH OH Figure 1. Organic diphosphonates synthesized ¿ The bistriazolylpyridine and terpyridine derivates successfully reacted with the surface phosphates of ¿¿ZrP by topotactic leading to materials where the chromophores were covalently attached to the ¿¿ZrP (Figure 2).
¿ Lanthanide metals were incorporated by very simple procedures to the porous hybrid materials obtained.
¿ Tuning of procedures for the photophysical study of the materials. Time¿resolved luminescent measurements (Figure 2) and quantum yields in solid¿state.
Figure 2. Exchanged ¿¿ZrP with chromophores derived from bis¿triazolylpyridine and phenylterpyridine, showing the characteristic emission of Eu3+ and Tb3+.
In a second stage of the research, the phosphonates with the core chromophore bis¿triazolylpyridine were re¿designed to make them contain stereocenters (Figure 3) and thus be intrinsically chiral in order to check whether this dissymmetric sensitizer is able to produce lanthanide CPL.
N N N N N N N OH P O OH O ¿ HO OH P O HO O ¿ OH 4 Figure 3. Chiral chromophore derived from the bis¿triazolylpyridine unit ¿ The synthesis was successfully accomplished and the building of the corresponding hybrid materials was effectively achieved.
¿ As a preliminary study, the terbium complexes formed with the chiral bistriazolylpyridine derivative in solution have been checked by CD and CPL, leading to quite significant activities that were explained not by the direct interaction of the metal with the stereocenters but by the induction of the latter of a highly dissymmetric environment around the metal.
Figure 4. CD spectra of the chiral ligands 4 and their Tb complexes in solution (10¿3 M in water) ¿ The Tb CPL signal observed in solution was fairly strong and highly structured, the two enantiomers of the chiral bis¿triazolylpyridine derivative showing signals that were exactly mirror images of each other (Figure 5).
¿ The optically pure diphosphonates have been successfully incorporated within the layers of ¿¿ZrP by topotactic exchange reaction (Figure 6 left).
¿ In order to build a different chiral scaffold, optically pure 1¿phenylethylamine (PEA) has been intercalated into the ¿¿ZrP¿based material containing the nonchiral bis¿triazolylpyridine (Figure 6 right).
¿15 ¿10 ¿5 0 5 10 15 300 320 340 360 380 400 Intensity (a.u.) Wavelength (nm) (RR)¿4 (SS)¿4 (RR)¿4:Tb (SS)¿4:Tb ¿¿ ¿0.02 ¿0.01 0.00 0.01 0.02 0.03 Wavelength (nm) 535 540 545 550 555 560 Intensity (arb. units) 0.0 0.2 0.4 0.6 0.8 1.0 SS¿4:Tb RR¿4:Tb Figure 5. CPL spectra of the terbium complexes with chiral ligands 4 Figure 6. Molecular models at the corresponding experimental interlayer distances of topotactically exchanged ¿¿ZrP with diphosphonates (SS)¿4 (left) and 1 with intercalated PEA (right).
¿ Lanthanide metals were incorporated by very simple procedures to the porous hybrid materials obtained.
¿ We measured the photophysical properties of the materials prepared in solidstate: steady¿state and time¿resolve luminescence (Figure 7), lifetimes and quantum yields. All of them gave rise to the characteristic bands of the Tb luminescence by the well¿known antenna effect.
240 320 400 480 560 Wavelength (nm) Figure 7. . Solid¿state eExcitation and time¿resolved luminescent spectra (delay= 0.1 ms) of the main materials under study derived from ¿¿ZrP that contain the chiral ligands 4 [(SS) in green and (RR) in blue)] and ligand 1 with chiral molecules of PEA [(+)¿PEA in orange and (¿)¿PEA in burgundy)] ¿ We have successfully performed for the first time solid¿state CPL measurements in hybrid materials (Figure 8).
¿ The chirality at the supramolecular level was revealed in the solid state by the CPL activity measured from reporter Tb (III) ions intercalated in the hybrid materials prepared. The observed CPL signals evidence that the dissymmetric structure of the layered ¿¿ZrP may induce preferential arrangements of the chiral guests, whose chiroptical properties are thus amplified or cancelled at the supramolecular level.
It is expected that the layered supramolecular scaffolds studied in this work and their optical properties in solid¿state will be valuable in the development of novel chiral supramolecular organic¿inorganic light¿emitting matrices.
Table 1. Photophysic parameters of metal emission of the studied materials ¿¿ZrP Material Ligand (%) Ln (%) ¿ Exc. ¿Lum Ln (%) ¿ (ms) BTP¿Eu 19 25 294 0.3 0.8 BTP¿Tb 19 25 300 0.6 1.0 BTP¿(+)PEA¿Tb 17 31 308 1.3 1.1 BTP¿(¿)PEA¿Tb 17 32 309 0.8 1.5 (RR)¿Tb 16 21 312 0.4 1.1 (SS)¿Tb 17 20 319 4.1 1.2 ¿I 0 2e-3 4e-3 6e-3 8e-3 1e-2 545 Wavelength (nm) 530 540 550 560 Intensity (arb. units) 0.0 0.2 0.4 0.6 0.8 1.0 545 ZrP-SS-Tb ZrP-RR-Tb ZrP-BTP-(+)PEA-Tb ZrP-BTP-(-)PEA-Tb KBr-ZrP-BTPSS-Tb 20% Figure 8. CPL spectra of the main materials under study derived from ¿¿ZrP that contain the chiral ligands 4 [(SS) in black, KBr¿20% (SS) in red and (RR) in blue)] and ligand 1 with chiral molecules of PEA [(+)¿PEA in purple and (¿)¿PEA in green)]
