Carbazole And Dithieno[3,2-b:2’,3’-d]Pyrrole Based Materials:Design, Synthesis And Properties

Organic light-emitting diodes (OLEDs) have been of great interest as promising candidates for applications in display and solid-state lighting in the past decades. These leading next-generation technologies for electronic displays are superior in that they are self-luminous, high-brightness, wide viewing angle, high contrast, thinness, low power consumption, fast response time and flexibility.As the key components of OLEDs, the development of organic light-emitting materials has great influences on the practical use of OLEDs to a great extent. Therefore, it would be of great importance in both theory and practice to study and explore highly efficient fluorescence materials. To meet the requirement of full color displays, suitable blue emitting materials with saturated color purities, high solid-state photoluminescence (PL) quantum yields and good stabilities are still needed further development compared to the red and green emitters. The ideal blue-light materials match the CIE coordinates of (0.14,0.08) as specified in the National Television System Committee (NTSC) standard. Until now, deep-blue emitters reported are still rare, and the realization of highly efficient OLEDs is also a big challenge because blue light is generated from wide-gap excited states.Helicene derivatives, structurally characterized by ortho-fusion of aromatic rings, are a class of chiral helical molecules. The twisted and noncoplanar helical configuration can prevent the close-packing interaction, so it will effectively relieve the excited-state quenching. Furthermore, the highly fused conjugated geometry can extend the π-system, which can balance the efficiency and the charge transport. Therefore, helicenes are theoretically potential candidates for emitting materials. In this thesis, using carbazole as the starting reactant, we synthesized a novel nitrogenous helicene with seven rings, namely2,12-dihexyl-2,12-diaza[7]helicene (1), by a traditional method of the oxidative photocyclization, and this compound used as a deep-blue dopant emitter for OLED was studied firstly and in-depthly. In particular, photocyclizded1was obtained in an exceedingly short time (ca.10min) with high productivity (80.5%). It was confirmed that1exhibited good solubility in common organic solvents, which overcame the formidable problem in syntheses of long helicenes as highly rigid and annelated structures. Meanwhile,1showed excellent thermostability with a decomposition temperature (Td) reaching372.1℃and a high glass transition temperature (Tg) up to203.0℃. Single-crystal structure analysis along with theoretical investigation revealed the non-planar fusion crystal structure of1made for reducing close-packing arrangement and keeping the molecule in a good amorphous state. Therefore, these merits can optimize electroluminescent behaviors. The OLED device with the structure of ITO/NPB (50nm)/CBP:5%1(30nm)/BCP (20nm)/Mg:Ag (100nm)/Ag (50nm) was fabricated and represented saturated blue light with the CIE coordinates of (0.15,0.10) located quite close to the NTSC standard blue CIE coordinates, and the maximum luminance efficiency and brightness were0.22cd A-1(0.09lm W-1) and2365cd m-2respectively.Crystal structures are very important for the study of the relationship between the compounds and physical properties. Crystallography and crystal engineering is a key visualized approach for studying the material structures. Crystal structures of title compounds were investigated by X-ray diffraction. The relationships between structures and optical, electrochemical and thermal properties were studied along with theoretical investigation. Meanwhile, the phase transformation of (E)-1,2-bis(4-hexyl-4H-dithieno[3,2-b:2’,3’-d]pyrrol-2-yl)ethane (b) in a high temperature range was studied in-depthly. Two clathrate crystals, namely (1)2·cyclohexane and (1)·(hexane)o.38, were obtained by the cosolvents-pervading and evaporating method. Thermal analysis combined with the crystal structures revealed that the solvent molecules were firmly inserted into the host holes by various short host-guest contacts. The novel clathrates based on carbazole have significant potential in supramolecular chemistry addressing manifold items such as crystal engineering.