Diseño y aplicaciones de materiales híbridos fotoactivos stars

Abstract

Along this PhD work, we have manifested the importance of incorporating photoactive materials into inorganic matrices, with the aim of improving their properties and expanding their potential applications. In this sense, it has been designed a synthetic route based on the Sol-Gel Coordination Chemistry with a great versatility, allowing us to obtain different types of photoactive hybrid silica- and titania-based materials. Comparative studies performed between materials prepared following the new in-situ approach and those obtained by post-synthetic strategies allowed us to show their more notable strengths. With this aim, we have synthetized and characterized several cationic Ir(III) and Pt(II) complexes of the type [Ir(C^N)2L2]+ and [Pt(C^N)L2]+, respectively, where C^N corresponds to cyclometalated ligands, and L to neutral bipyridine and phosphine ligands functionalized with trialkoxysilane groups (PPTES = PPh2(CH2)2Si(OEt)3, dasipy = 4,4’-[CONH(CH2)3Si(OEt)3]2-bipyridine). After the study of their photophysical properties, we prepared the corresponding hybrid organometallo-silica materials following the in-situ approximation. It has been demonstrated that this technique can be easily adapted to chromophores with different structural and electronic features (octahedral or square-planar geometries, cationic or neutral derivatives, with one or several alkoxysilane groups). In addition, using a single silica source (TEOS) and just slightly modifying the reaction conditions, luminescent hybrid silica-based materials with different morphologies and textural properties have been obtained. Thus, we have prepared macroscopic nanostructured materials (SiO2_P and SiO2_G) and discrete nanoparticles with different superficial modifications (NPOH, NPMe and NPAPTES). Generally, the new hybrid materials display better physical properties and stabilities than those of the organometallic chromophores incorporated. This methodology is relatively flexible and has allowed us to obtain materials that mimic the photoemission of the organometallic precursor in the solid state or in solution, depending on the concentration used. All these features allowed us to use these hybrid silica materials in a wide range of topics as optically transparent gels, light emitting devices or biomarkers. Thus, and thanks to collaborations with the research groups of Dr. Rubén D. Costa (IMDEA Materiales, Madrid) and Dr. José Manuel García Pichel (Centro de Investigación Biomédica de La Rioja, CIBIR), we have tested the silicas as substrates for the fabrication of white-emitting LEDs and as biomarkers, respectively. On the other hand, we have successfully adapted this Sol-Gel Coordination Chemistry approach to the preparation of titania-based materials. With is aim, we synthetized two Ir(III) and Ru(II) complexes, bearing bipyridine ligands with carboxylic groups, [Ir(ppy)2(3,3’-H2dcbpy)]PF6 y [Ru(4,4’-H2dcbpy)2(NCS)2]. The condensation reaction between them and TBOT yield hybrid titania materials (TiO2_IS) with narrower band gaps than those observed for the complex-free control titania and for other materials obtained following post-synthetic techniques (TiO2_G). All these features are the responsible of their improved photocatalytic performance, not only under UV light but also under visible irradiation. This fact, unprecedented in the bibliography, allows to broaden the possibilities for the design of new and stable photoactive materials, able to be used after several catalytic cycles for the photodegradation of organic compounds. This improved stability should be attributed to the good integration of the photoactive complexes inside the anatase matrix, which provides them with additional protection and stability. All these features, together with the ease modulation of the reaction conditions and the extra protection provided by the inorganic matrix to the incorporated chromophores, represent an important advance in the design of photoactive systems.