Synthesis And Characterization Of Thieno-[3,4-b]-pyrazine Derivatives For Red Light-emitting Materials

Organic light-emitting diodes (OLED) have received great attention in science and industry by virtue of the particular advantages such as self-luminous, direct current driving, full color emission, high luminescence and simple manufacture techniques. As one of the primary colors (red, green and blue), the red emitters are required for full-color applications and white-light lighting. However, due to the poor thermal stability, short lifetime and easy to fluorescence quenching, these emitters are still lag behind green and blue materials which have been already commercially available. It is essential to develop new red emitters and improve the luminance and efficiency.To date, an effective way to solve the fluorescent quenching effect and reduce the cost of device production is to design and synthesize red host emitters that are capable of being made non-doped OLEDs. Dendrimers with well-defind three dimensional dendritic structures are perfectly able to be served for this demand. The thieno-[3.4-b]-pyrazine derivatives were proved to be a series of potential red materials which have large Stokes shifts, high fluorescent quantum efficiency and thermal stability. However, they still have some disadvantages such as poor solubility and fluorescent quenching. Therefore, a series of red light-emitting dendrimers based on thieno-[3.4-b]-pyrazine core with tetraphenylethylene (TPE) dendron were successfully prepared via Suzuki coupling. All of them have good solubility in common solvents. And their structures were conveniently confirmed by MALDI-TOF-MS and1H NMR.The T-TP and T-TP1dendrimers start to decompose at a high temperature up to400℃, indicating the excellent thermal stability. They were used as non-doped emitting layer to fabricate OLEDs by vacuum evaporated technique. The structure of the device was ITO/PEDOT:PSS (40nm)/EML (40nm)/TPBI (40nm)/LiF (1nm)/Al (100nm). The EL spectra are located at saturate red region. The devices exhibited the maximum brightness of1385cd m-2and1400cd m-2and luminous efficiency of0.66cd A-1and0.54cd A-1for T-TP and T-TP1, respectively. The CIE coordinates are (0.65,0.32), and (0.66.0.30) at10V, respectively, which are quite close to the pure red light (0.64,0.33). These are the better data among the devices based on Thieno-[3.4-b]-pyrazine materials. The two devices based on reported dendrimers in this paper show good color purity and luminous property and they are promising non-doped red-emitting organic materials.