Strategies for sustainable photocatalysishybrid organometallo-silica materials and BODIPYs stars

Abstract

The great development experienced in recent years in the use of photocatalytic reactions in the synthesis of highly relevant organic compounds, together with the progressive application of these reactions in industry, has made it desirable to search for more sustainable photocatalytic systems. Although several strategies are being explored, in the context of this thesis two main ones have been studied: the heterogenization of emissive organometallic iridium(III) complexes, and the use of organic photocatalysts. In Chapter 1, we have carried out the heterogeneization of the iridium(III) complex [Ir(dfppy)2(dasipy)]PF6, which has two triethoxysilane groups in its structure. By means of post-synthetic functionalization methods, a material formed by mesoporous silica nanoparticles with the complex incorporated by superficial covalent bonding (grafting) techniques has been synthesized. Four other silica-based materials have been obtained by in-situ functionalization methods. Three of them are hybrid silica gels, while the fourth is formed by discrete nanoparticles (NP_IS). After studying their textural and photophysical properties, their photocatalytic activity has been evaluated in the trans-stilbene isomerization reaction. Once the reaction conditions were optimized, the recoverability of the five materials was studied, analyzing the influence of the morphology and the functionalization method on their reusability. In Chapter 2 a new material was synthesized, based on the same cationic complex used in chapter 1. However, for this synthesis no additional source of silica was added, resulting in a new kind of ionic material composed entirely of covalently bonded molecules of the complex. After studying the textural and photophysical properties of the material, it was used as a photocatalyst in two photoredox reactions, the photocatalytic dehalogenation of 2-bromoacetophenone, and the synthesis of phenanthridine from acyloximes. After optimizing the reaction conditions, the recovery and recyclability of the material in successive catalytic cycles was also studied. Finally, in Chapter 3, we have developed the synthesis of four compounds based on the structure of BODIPYs with phenylpyridine groups in the meso position. Two methods to improve the ISC efficiency have been studied. Firstly, the well-known influence of iodination of the alpha positions of the BODIPY fragment and, secondly, the possibility of orthogonalization of the phenylpyridine group, with formation of a D-A system. Following the study of its photophysical properties, the singlet oxygen quantum yield of the four BODIPYs was measured, as well as their use in the photocatalytic reaction of the oxidation of dibenzylamine.