NEW NAPHTHALIMIDE DERIVATIVES FOR ORGANIC LIGHT-EMITTING DIODE APPLICATION

Abstract

Three new triphenylamino naphthalimides (TPN1-3) are successfully synthesized by means of Suzuki cross-coupling between N-phenyl-1,8-naphthalimide and triphenylamine precursors. In CHCl3 solution phase, their maximum absorption wavelengths are around 430-433 nm while the maximum emission wavelength at 564-599 nm with quantum yields in the range of 0.18 to 0.29 in CHCl3. In solid thin-film state where the packing force enhances the conjugated system and prevents the molecular vibration, their absorption bands move towards longer wavelengths and the emission peaks shift to a shorter wavelengths. These compounds show excellent thermal stabilities with the 10% weight loss temperatures well above 350 °C. Results from the electrochemical investigation by cyclic voltammetry agrees with the data from computational calculations using Gaussian 09 code with B3LYP/6-31G(d,p) geometry optimizations. When the multi-layer OLED device of structure ITO/PEDOT:PSS/TPN1:CBP/BCP/LiF/Al is fabricated, a maximum brightness of 10,404 cd/m2 of yellowish green light at an applied voltage of 19 V with a turn-on voltage of 5.8 V are observed. The effect of solubility of these compounds on device performance is proven by AFM images of the spin-casted thin films.