A Systematic Study of Acene Derivatives: Synthesis, Crystal Structures, Optical and Electrochemical Characterizations

Abstract

This Thesis describes a systematic study towards a series of polycyclic aromatic hydrocarbons (PAHs). The objectives are to develop convenient and efficient synthetic approaches to unique aromatic frameworks in order to probe their optical and electronic properties. The ultimate goal for these studies is to establish structure−property relationships in organic electronic materials. Chapter 1 of this Thesis briefly reviewed the history and current challenge in organic electronic materials. In Chapter 2, the study of a benchmark p-type organic semiconductive material – rubrene is described. Fluorination, a strategy often used to tune the crystallographic and opto-electronic properties, is involved. Synthetic routes to partially and fully fluorinated rubrene derivatives are developed. The effect of fluorination is examined by optical and electrochemical measurements, and more importantly, by the influence on the crystal packing motifs. Fluorine-based intermolecular interactions are found to play an important role in the assembly of rubrene crystals. Chapter 3 elaborates on the work in developing a new type of PAH – dibenzo[g,s]rubicene, the structure of which contains five-membered rings that are embedded in a large conjugated core structure. The synthesis takes advantage of dehydro-Diels−Alder reactions as a powerful and highly efficient method to access the polycyclic conjugated system. The functionalized rubicene derivatives are then characterized by optical, electrochemical and computational methods. This work contributes to discovery of potential candidates for innovative n-type organic semiconductors. In chapter 4, synthetic studies toward a carbon nanobelt – [12]cyclacene are performed. Though previous reports have made significant achievements in the construction of a macrocyclic framework, however, late-stage modification to install the fully conjugated structure is proved to be challenging. In this work, a new strategy involving a thermally-driven cheletropic rearrangement is proposed to address the late-stage modification issue. In the effort towards the macrocycle synthesis, an advanced intermediate has been successfully obtained in a stereoselective manner via multiple stereoselective Diels−Alder reactions. The selectivity is attributed to the careful design of precursors, which afforded the desired products through a sterically favored reaction pathway. A detailed examination of the proposed synthetic route as well as the proposal of a more convenient route are illustrated in the end.