Design, Synthesis And Properties Study Of Ladder-Conjugated N-type Materials For Small Molecules

With the rapid development of organic electronics, it’s very important to develop the N-type semiconductor materials with good stability, high electron mobility and facile processability in recent decades. According to molecular weight, organic semiconductor materials can be classified as small molecules and polymers. Organic small molecules which are different from polymers, have many advantages, such as defined molecular structure and molecular weight, easy separation and purification etc. In this dissertation, under the guidance of the organic synthesis and the design principle of organic semiconductor, some ladder-conjugated organic small molecules were designed and synthesized, and their optical and electrochemical properties were studied.1. Based on perylene monoimide2G, five target compounds were synthesized by bromination, boric acid esterification, Suzuki coupling and cyclodehydrogenation. But the solubility of compound2N was too poor to characterize, and its structure was confirmed by MALDI-TOF-MS. Compared with compound2G, the other four compounds all show wider absorbance range, bathochromic-shift of maximum absorption peak position and increased molar extinction coefficient.2M,20and2J have the ability to accept one hole and three electrons, and their LUMO energy level is0.05eV lower than2G.2P has three groups of reversible reduction peaks, and its LUMO energy level is dropped to-3.90eV. We used these compounds as N-type materials, and blended with P3HT to fabricate BHJ solar cells respectively. The highest power conversion efficiency was acquired from2J, which was1.14%.2. By the strategy of controllable synthesis, compound3Q was designed and synthesized. This synthetic strategy could effectively avoid the isomers of peryleneimidazole class, and the target compound has the defined structure. In toluene, the maximum absorption peak position of3Q is614nm, and it keeps the high molar extinction coefficient. Attractively, the absorbance range of3Q is300-700nm, and it realized the mainly coverage of the visible region.3Q has the ability to accept two electrons, its LUMO energy level is0.03eV lower than perylene bisimide31, and it has stronger electron accepting ability. The method of space charge limited current was used to test its electron mobility (μe), which was1.01*10-5cm2V-1s-1. 3. Used the strategy of controllable synthesis, three novel ladder-conjugated chromophores4E,4H and41were designed and synthesized. Compound4E shows good two-photon absorption cross-section (8) up to1200GM at810nm in THF, which is attributed to intramolecular charge transfer effect, as supported by density functional theory theoretical calculations. Compounds4H and41show considerable molar extinction coefficients, which are more than105, and higher quantum yields. Structure-function relationship is further discussed, suggesting a rational strategy to develop ladder-conjugated small molecules.