Carbnyl Functionalized Alkyl Quinacridone Materials: Synthesis, Characterization And Applications

Quinacridone (QA) and its derivatives are the well-known organic pigments and dopant emitters that show excellent chemical stability and fastness properties. Moreover, as a type of classical fluorescent material, QA and its derivatives are widely utilized in fabrication of high-performance OLEDs due to their many advantages such as high photoluminescent (PL) efficiency and good electrochemical stability as well as the pronounced photoelectric activities. More importantly, QA derivatives are relatively inexpensive and could be readily modified; these advantages make them much more suitable for the commercial uses.The molecular structure of QA can be varied by introducing some functional groups to the benzene rings directly or modified by attaching lateral alkyl chain to'N'heteroatom. To the best of our knowledge, the functionalization on carbonyl positions of QA and exploration of application of such compounds has rarely been carried out except our group. Herein we purposefully designed and synthesized four novel series of quinacridone based materials for very important phenomenon of modern research by functionalization at the carbonyl positions of alkyl substituted quinacridone, these phenomena are (a) Organic solar cells (b) Aggregation induced emission (c) One dimensional self assembly and (d) Polymorphism.1. In chapter 2, we designed and synthesized two novel series of organic dyes by incorporating NC-CH2-COOH as electron withdrawing group at the carbonyl positions of QA skeleton. We studied photophysical, electrochemical, thermodynamic and photovoltaic properties of these compounds. By introducing electron withdrawing cyano- acetic acid groups, the absorption of alkyl substituted quinacridone has significantly red shifted which indicates the feasibility of obtaining narrow band gap material by enhancing intermolecular charge transfer transition effect. In addition these compounds have good solubility, high thermo-stability, stable electrochemical properties and proper energy level match with P3HT (donor) suggesting that they are good candidates for bulk-heterojunction solar cells. The bulk heterojunction Solar cells using P3HT as a donor and these novel synthesized materials as acceptor were prepared and characterized. By using acceptor with intense absorption in the visible spectrum, the solar spectrum response range of the former P3HT: PCBM device has been expanded from 650 nm to about 700 nm. One of the devices using 8CQA monocyclic compound 5 achieved the power conversion efficiency of 0.42 % with open circuit voltage of 0.50 V and fill factor of 47 %. Moreover the impact of alkyl chain length on the molecule aggregation behavior, the morphology of the active layer and the corresponding performance of the device are also discussed.2. In chapter 3, we designed and synthesized a new series of red emitting AIE active compounds (1-3) based on quinacridone (QA) by introducing 2-(3, 5-bis (trifluoromethyl) phenyl) acetonitrile at carbonyl position for tuning the optical and electrical properties. Absorption as well as redox properties of the compounds were measured. As the materials are commonly used as thin solid film in real world applications for making photonic devices, so, importance of photoluminescence properties in solid state is discussed. Photoluminescence in different solvents and at different temperature were measured to get insight into the aggregation induced emission phenomenon of these compounds. Moreover the impact of transition of crystalline and amorphous aggregates on photoluminescence is also discussed. The photoluminescence quantum efficiency of these bright red emitting compounds in the solid state and in solution state was measured and compared which shows that PL quantum efficiency of these compounds in the solid state is approximately 400 times greater than in the solution state.3. In chapter 4, by keeping in mind the red emission of the above mentioned AIE active compounds and significance of 1_D self assembly we grow 1_D nano/microwires by reprecipitation and evaporation approaches. Although our group has already successfully constructed luminescent nano/microwires based on alkyl substituted quinacridone (QA) but the photoluminescent quantum yields of the nanoscale wires were very low (0.19?2.0%) due to the ACQ effect. Herein we obtained highly fluorescent microwires based on novel series of quinoacridine derivatves. The impact of alkyl chain length on the length-diameter ratio in various solvent is discussed. To achieve deep understanding into structure-morphology relationship we systematically studied electronic effect and morphology transition in the self assembling process of these compounds from 0-D hollow nanospheres to 1-D nanotubes and 1-D microwires.4. In chapter 5, a series of QA diimine derivatives (1-10) were synthesized by the condensation of alkyl substituted quinacridones with aromatic amines. A detailed study is carried out for in-depth structural exploration of compounds 1-10 through simulation models and single crystal X-ray analysis. On the basis of detailed computational study by optimizing geometries of molecular orbitals and by measuring variable temperature 1HNMR spectrum we concluded that these QA derivatives exist in different conformational isomeric forms at different temperatures with buckled QA skeleton in non-planer fashion. Photophysical and redox properties of all the derivatives were measured and relationship between structure and optoelectronic properties was evaluated.