Design, Synthesis and Physical Properties Evaluation of Heptagon-Containing Distorted Nanographenes

Abstract

After a short description of the graphene preparation methodologies, the graphene nanoribbons are introduced. Particularly, a strong emphasis on the in solution “bottom-up” preparation of graphene nanoribbons is made, although “top-down” and on-surface techniques are also mentioned. This section also allows to introduce the structure of polyphenylene compounds, key structures on the next section. The main part of the introduction section is focused on the structure and synthesis of nanographenes. Firstly, their structure, synthesis and properties will be reported. In this section, the synthetic methodologies based on alkyne cyclotrimerization reactions or Diels-Alder reactions in combination with Scholl-type reaction will be described. Among these methodologies, an explanation of the mechanism of the alkyne cyclotrimerization reaction and the Scholl reaction will be found. Likewise, the basis of the two-photon absorption technique are detailed followed by examples of structurally related extended nanographenes as a background on the field were this thesis is found. Lastly, alternative methodologies for the preparation of nanographenes are described. Subsequently, a description of the structure of carbo[n]helicenes can be found along with two of the most important associated chiroptical properties: i) circular dichroism, and ii) circularly polarized luminescence. The structure and properties of the most relevant helicenes, both simple and extended take up the next section, ending on the introduction of a new family of helical nanographenes, the superhelicenes. As extension for the structures containing one helicene, the structure and properties of multiple-helicene compounds are described, comparing the properties of simple compounds with their π-extended analogues. This section ends with the most relevant and actual examples of extended nanographenes bearing multiple helicenes. The introduction and background ends talking about non-hexagonal ring-containing nanographens, from the simplest structures such as [n]circulenes to examples of extended nanographenes. At the same time, the reported methodologies for the preparation of this family of nanographenes are described. Regarding the background on the field, the objectives of the thesis are disclosed. The results and discussion of the information obtained is structured as follows for each prepared compound: i) the methodology applied for the preparation of the different nanographenes combining both heptagons and helicenes, ii) the structural characterization of these compounds, iii) the study of their optical and chiroptical properties, iv) the study of their electrochemical properties, and v) the study of other properties such as surface imaging. The last section gathers the experimental data corresponding to the used techniques during the thesis, as well as a detailed description of the synthesis of the prepared compounds and its structural characterization. Lastly, the obtained conclusions of the work developed in this thesis can be found. Additionally, we have included other results obtained during the development of this thesis that can be found as annexes.