POLY(P-PHENYLENE VINYLENE) AND ACENE BASED SEMICONDUCTING MATERIALS

Abstract

The demand for low-cost, large area, flexible and lightweight devices drives the development of electronic circuits and displays using organic and polymeric semiconducting materials. The fabrication of organic electronics, such as complementary integrated circuits, bipolar transistors, or p/n junctions, requires both the materials capable of transporting holes (p-type semiconductor materials) and materials capable of transporting electrons (n-type semiconductor materials). However, development of n-type organic semiconductors has lagged far behind that of p-type organic semiconductor material. One reason is assigned to the low stability of most n-type organic semiconductors in air. Therefore, the search of n-type organic semiconductors material with high performance and environmental stability is currently a challenge and of great importance. This PHD thesis will deal with our attempts to prepare novel air-stable n-type semiconductor materials and can be classified as two efforts: 1) development of novel n-type organic semiconductor materials based on the existed p systems, specifically from poly(p-phenylene vinylene)s (PPVs) and pentacene; 2) exploration of new extended p systems (high order acene). In chapter 1, the recent progress in air stable n-channel semiconductors and the chemistry of high order acenes was reviewed separately. In chapter 2, our efforts of constructing n-type organic semiconductor materials from PPV were detailed. Three PPV polymers with electron-withdrawing dicarboxylic imide moiety attached on each phenyl ring were synthesized by using Wittig-Horner reaction. These polymers were found to have good thermal stability, a high electron affinity (3.60 eV), and highly ordered packing in the solid state via ¿-¿ interactions. These polymers show promise for use in n-channel field effect transistors (n-FETs) and polymer-based solar cells. In chapter 3, we demonstrated our strategy of converting pentacene, an air-unstable high-performance p-type semiconductor material, to air stable n-type semiconductor materials by introducing strong electron withdrawing substitutes. In this study, a meso-brominated pentacene was firstly prepared which was an important intermediate for various palladium catalyzed coupling reactions, such as Suzuki, Stille, cynation, Hagihara-Sonogashira reactions. Therefore, a series of pentacene diimide derivatives have been prepared, and they show interesting optical and electronic properties. Among them, the dimethylaminophenylacetylene-substituted pentacene diimide showed extremely high photostability with half-life time of nearly one month. The cyano-substituted pentacene diimide displayed a low-lying LUMO energy level of -4.19 eV which is promising candidate for n-channel FET material. In chapters 4 and 5, the synthesis of stable heptacene and nonacene derivatives was attempted. Knowing that instability was the weakness of high order acenes such as heptacene and nonacene, the functionalization strategies to enhance the stability of high order acenes were explored in these chapters. We successfully synthesized a soluble and stable heptacene derivative by introducing electro-withdrawing trifluoromethylphenyl groups and triisopropylsilyl ethynyl units. It represents the most stable heptacene reported so far. In addition, we also got breakthrough for the preparation of stable nonacene derivatives. Our methodologies open the opportunity to make high performance materials based on these molecules.