Synthesis and Light-Emitting Properties of New Polyimides Containing Ethynylene Units in the Main Chain

Abstract

Two new polyimides (ODA-PI and HDA-PI) having 1,4-phenylenediethynylene unit and octyloxy groups were synthesized. Judging from inherent viscosities of their precursor PAAs (1.42 and 1.62 dL · g-1), the two PIs were very high in molecular weight. Casting and thermal imidization of PAAs results polyimides with good-quality films. They were stable up to 364 °C and showed no crystallites. UV-vis and PL spectra in NMP solutions of both PIs showed maxima at 442 and 501 nm, respectively, while PL spectra in 10 µm thick films exhibited a maximum at 540 nm. CV indicates that two PIs were electrochemically active in redox region. The devices with construction of ITO/PEDOT/PIs/BAlq3/LiF/Al exhibited turn-on voltages of 6.5 V in ODA-PI and 7.5 V in HDA-PI and emitted a bright bluish-green light. ODA-PI and HDA-PI showed maximum luminescence of 256 and 316 cd · cm-2, respectively, at the same voltage of 12 V.