Synthesis And Characterization Of Alcohol-Soluble Electron Injection/Transport Molecular Materials

Because of the potential applications in flat panel displays and solid-state lighting, organic light-emitting diodes (OLEDs) have drawn greet attention. For OLEDs, efficient electron injection from various metal cathodes has been a subject of intensive research. The early OLEDs have used low work-function metals such as Ca and Mg as efficient cathodes. However, these metals are very sensitive to both moisture and oxygen. Thus it is very important to develop new cathode buffer materials that are capable of facilitating electron injection from more environmentally stable metals such as Al, Ag or Au. Up to now, a variety of electron-injection materials including inorganic salts, conjugated polyelectrolytes and non-ionic molecules or polymers have been reported. This thesis mainly focuses on the synthesis and characterization of new solution processable small molecular electron-injection moleculars.We first reported a monoammonium-based molecular glass containing a rigid and bulky branched aromatic unit, namely glass-1. It can be facilely synthesized and purified, showing good solubility in methanol. For instance, 10 mg of the sample can be readily dissolved in 1 ml of methanol at room temperature, so it can be processed from methanol solution. With this monoammonium salt as electron injection layer, a polymer yellow-green light-emitting device (ITO/PEDOT:PSS/P-PPV/glass-1/Al) shows a maximum current efficiency of 12.2 cd A-1, almost forty-two times higher than the bare Al device, which is comparable to that of the Ba/Al device.Further, we designed and synthesized a series of molecular monoammonium salts based on a linear?-conjugated unit, namely 1a/1b and 2a/2b. Replacement of the ethyl groups in 1a/1b by ethoxyphenyl substituents at one of the two fluorenyl moieties can improve the solubility in methanol and promote glass formation of compounds 2a/2b. It has been found that 2a and 2b show better device performances than 1a and 1b, respectively. In addition, the counteranion has an important effect on the device performances of the OLEDs as well as on solubility and thermal properties of the resulting ionic salts. ?Based on the above monoammonium salts, we developed two types of bis-ammonium salts, namely dBr-1/dBF₄-1 and dBr-2/dBF₄-2. Compared to dBr-1/dBF₄-1, compounds dBr-2/dBF₄-2 containing 3-(4-sec-butoxyphenyl)-5-(1-naphthyl)phenyl substituents show better solubility in alcohol. The green light-emitting OLEDs based on the bis-ammonium salt dBF₄-2 and monoammonium salt 2b as the electron-injection layers and Al as the cathode show comparable performances.We have also designed and synthesized two non-ionic molecules, which were named as PA-1 and PA-2. Compounds PA-1 and PA-2 are based on diamine and triamine, respectively. The green light-emitting device with PA-2 as the electron-injection/transport layer and high work-function metal Al as cathode revealed a maximal efficiency of 10.6 cd A^-1.