Síntesis y medidas de las propiedades electrónicas de dirradicales orgánicos

Abstract

The present Doctoral Thesis is entitled "Synthesis and measurements of the electronic properties of organic diradicals". It is divided into the following sections: i) a general Introduction, which aim to contextualize the research developed within this Thesis; ii) the Objectives proposed in this dissertation; iii) the Results and discussion, where the work carried out for each objective is shown and compared with results already reported in literature; iv) an Experimental Section, where experimental procedures and characterization of new compound are provided and, finally, v) the general Conclusions obtained for this dissertation. The general Introduction is divided into two sections. In the first part, a brief explanation about what radicals are focusing on the term diradical. Once this concept is described, the section continues to explain what indenofluorene (IF) structures are and why they are interesting molecules to study. In addition, a review is reported including the most important and up-to-date examples of IF-type structures described in the literature. In this section, a detailed compilation of both the diversity of IF-type structures described to date, as well as the optical and electrochemical properties of these IF examples, can be found. In the second part of this Introduction, the theoretical basis of unimolecular conductance is explained, focusing on the STM-BJ (scanning tunneling microscopy-break juctions) technique. Lastly, the relationship between the aromaticity of molecules and the singlemolecule conductance is discussed, followed by a compilation of studies of unimolecular conductance on radical molecules reported to date The Results and discussion section follows a division by objectives. Concerning objective 1, unimolecular conductance is measured for three structural isomers of IF ([1,2-b], [2,1-b] and [2,1-c]). They are formally antiaromatic molecules with different diradical character index (y), being the first time that unimolecular conductance is measured for such molecules and the first example of conductance measurement of an open-shell diradical. In addition, their optical and electrochemical properties are analyzed and compared with other examples already reported in the literature. Respect to objective 2, eight derivatives of the [1,2-b]IF type are synthesized. A change in the opto-electronic and diradical properties of the IFs has been observed by varying the substituents placed in the apical positions of the IF structure, from more electron-donating to more electron-withdrawing groups. On the other hand, molecular conductance measurements have also been analyzed for one of these IF derivatives. High conductance values were observed due to the narrow HOMO-LUMO gap of these new class of molecules. Finally, concerning objective 3, the synthesis of three dihydroindenofluorenes have been carried out. These molecules are precursors of interest for on-surface synthesis of diradicals and consist of the basic skeleton of di- or polyradicals synthesized in solution by our or other research groups. Studying these molecules on-surface will allow us to evaluate both their topology and their magnetic properties. The Experimental Section shows the most interesting results corresponding to the techniques used during this thesis, as well as a description of the synthesis of the compounds and their structural characterization. Finally, the general Conclusions for the three objectives are drawn. In addition, some Annexes are provided, showing a list of publications obtained during the pre-doctoral studies and then, a list of references used for the non-original figures of this manuscript.