Design,Synthesis And Optoelectronic Properties Of Organic Blue Molecules Based On Fluorene As A Core

Organic light-emitting diodes（OLEDs）have shown great prospects as novel display and lighting technology.The blue emitters with excellent properties are currently the most important segment for development of the OLED.This paper focused on the problem of carrier injection/transport in blue emitters,realized the blue molecules with high and balanced carrier mobility,obtained the blue OLEDs with high efficiency and low efficiency roll-off through designing molecular structure reasonably.The specific research contents are as follows:1.Based on carbazole（CZ）derivatives and triphenylamine（TPA）as the donors,the oxadiazole（OXZ）as the acceptor,three donor-acceptor（D-A）blue molecules were designed and synthesized:9-PCZOXZ、3-PCZOXZ and TPAOXZ.The three molecules exhibit red shift gradually and high photoluminescent quantum yield（PLQY）of over80%by the test of photophysical property.The non-doped OLEDs of 9-PCZOXZ and3-PCZOXZ possess more decent light colors with the Commission Internationale de l Eclairage（CIE）coordinates of（0.157,0.076）and（0.155,0.073）.The electron mobility of three molecules are 10^-5～10^-4 cm~2 V^-1 s^-1,which is 3 orders of magnitude higher than their hole mobility.This work not only explored the effects on the electroluminescence performances systematically from different donors,but also revealed that the oxadiazole acceptor unit with a planar structure is beneficial to improve the electron mobility in the blue material.2.Based on the same donor-acceptor unit,three D-π-A blue molecules with the fluoreneπ-bridge were designed and synthesized（9-PCZCFOXZ,3-PCZCFOXZ and TPACFOXZ）,and their non-doped OLEDs were prepared.Three D-π-A molecules have higher efficiency and better light color than three D-A molecules,in which 9-PCZCFOXZ and 3-PCZCFOXZ maintain high color purity with CIE coordinates of（0.154,0.076）and（0.149,0.109）.The non-doped OLED of 3-PCZCFOXZ and TPACFOXZ exhibits a high maximum external quantum efficiency of 8.5%and 9.8%,and no efficiency roll-off at the luminescence of 1000 cd m^‐2.This result has far exceeded international similar non-doped blue OLED.The study found the fluoreneπ-bridge has dual functions,which is not only conducive to formation of hybrid local and charge-transfer states（HLCT states）to gain high efficiency,but also regulated packing mode between molecules,so that the carrier mobility is improved and balanced.The hole mobility can be gradually improved,reached the balanced carrier mobility finally(The electron mobility and hole mobility of TPACFOXZ are 6.60×10^-5 cm~2 V^-1 s^-1and 5.60×10^-5 cm~2 V^-1 s^-1)and controlled light color（blue to deep-blue）by adjusting the species and the bonding position of donors.This work regulated the carrier mobility precisely by the fluoreneπ-bridge,resolved the problem between wide bandgap and high carrier injection/transport in blue materials,and revealed that the fluoreneπ-bridge have great potential advantages in D-π-A blue molecular,which is of great significance for the design of blue non-doped OLEDs with excellent performance.