Synthesis And Properties Of The2,7-fluorene Derivatives Contanting Bipolar Transporting Units And/or Iridium Complex Chromophore

The development history and status of organic/polymeric electroluminescentmaterials and their light-emitting devices were described, as well as the developedpolymeric electroluminescent materials and electrophosphorescent materials werereviewed in this dissertation. At present, the organic small molecules-based phos-phorescent devices have achieved great success with high-efficiency emission. Butthere exists the problem of phase separation during the long period of operation,which leads to lower device’s lifetime, and severely restricts their application inOLEDs/PLEDs. The electrophosphorescent polymers can be structured by covalentlinkage between the cyclometalated complex chromophores and the polymeric mainchain or side chain. This class of electrophosphorescent polymers can be synthesizedwith simple method and their emitting colour can be tuned easily. Furthermore, theirPLEDs can be made with simple technology and have excellent stability at highercurrent density. Therefore, this class of electrophosphorescent polymers has asignificant potential in PLEDs. However, PLEDs using these electrophosphorescentpolymers as emitters have low luminescent efficiency yet. To further study therelationship between the molecular structure and photoelectric property, as well asdevelop the polyfluorene derivatives used in PLEDs and improve the electro-luminescent property in their PLEDs, a series of the bipolar-transporting polyfluorenederivatives used as electrofluorescent and electrophosphorescent materials were de-signed and synthesized, in which the bipolar-transporting groups and iridium（III）bi（phenylisoquilonato）（picolinato） chromophores were attached into the C-9positionsof fluorenes by non-conjugated linkage. Their photophysical property, thermalstability and electrochemical property, as well as electroluminescent property insingle-emissive-layer PLEDs were measured. The influence of bipolar transportinggroups, cyclometalated iridium complexes chromophores, terminal groups andconstructure manner on the property of these polyfluorene derivatives was furtherstudied. The main research work in this dissertation was listed as following:1. A series of novel non-conjugated polyfluorene derivatives （P₁-P₄） used aselectrofluorescent and electrophosphorescent materials, as well as the bipolar-transporting polyfluorene derivatives （P₅-P₆） attached different terminal group used as electrophosphorescent materials, were designed and synthesized, in whichthe carbazole and oxadiazole groups, the red-emitting iridium（III） bi（phenyliso-quilonato）（picolinato） unit were pending into the C-9position of fluorene byunconjugated linkage of the alkyl and alkoxy gruops, respectively.2. The photophysical property, thermal stability and electrochemical property ofpolyfluorene derivatives （P₁-P₆） were measured. Their excellent thermal stabilitywas presented. All of these polyfluorene derivatives exhibited similar photo-luminescent （P_L） spectra with a maximum peak at417nm and a shoulder at440nm in their dilute dichloromethane （DCM）. The bipolar-transporting polyfluorenederivatives P₃-P₆displayed similar UV-absorption spectra with a maximum peakat380nm and a moderate peak at290nm in their dilute DCM. On the other hand,the bipolar-transporting polyfluorene derivatives P₄-P₆and the unfunctionalizedpolyfluorene derivative P₂used as electrophosphorescent material also showedsimilar P_L spectra with a maximum peak at623nm and a weak peak at440nm intheir thin films. The bipolar-transporting polyfluorene derivative P₃used aselectrofluorescent material exhibited a P_L spectrum with a peak at443nm andanother peak at556nm resulting from the fluorene framework and excimer,respectively. However, the bipolar-transporting polyfluorene derivatives P₃-P₆exhibited higher thermal decomposition temperatures over58oC than the un-functionalized polyfluorene derivatives P₁and P₂. It indicated that the incorpo-ration of bipolar-transporting units of carbazole and oxadiazole in the side chainof the polyfluorene by non-conjugated linkage is available to improve the thermalstability and photoelectric property for their resultant polyfluorene derivatives.3. The electroluminescent （EL） property of their single-emissive-layer PLEDs werefurther measured with a configuration of ITO/P_EDOT:P_SS （50nm）/polymers/LiF （0.5nm）/Al （150nm）. The P₃-based device presented the best deviceperformance among the devices using the polyfluorene derivatives aselectrofluorescent materials. The maximum EL peak at560nm, the maximumcurrent efficiency of0.47cd/A and the maximum luminance of1032cd/m²wereobtained in the P₃-based device. On the other hand, the bipolar-transporting poly-fluorene derivative P₅-based device exhibited the best device performance amongthe devices using the polyfluorene derivatives as electrophosphorescent materialsas P₅was end capped by another oxadiazole unit. The maximum EL peak at623nm, the maximum current efficiency of0.54cd/A and the maximum luminance of1299cd/m²were obtained in the P₅-based device. The incorporation of theoxadiazole terminal group in the polyfluorene derivatives is available to suppresstheir excimer emission, improve emissive colour stability and luminous efficiencyfor their PLEDs.