Synthesis and Characterization of Organic Light-Emitting Copolymers Containing Naphthalene

Conjugated PPV-derived block copolymers containing 2-ethylhexyloxynaphthalene unit were synthesized and characterized in this study. The resulting polymers were soluble in common organic solvents and showed good thermal stabilities. The weight-average molecular weights ( M w ) of the copolymers ranged from 246,000 to 475,000 with PDIs of 1.3∼2.1. The optical properties of these polymers, measured both in a chloroform solution and on a film, showed a maximum absorption at 405∼476 nm for Copolymers I∼VIII. In the PL spectra, Copolymers I∼VIII showed maximum peaks at 510∼566 nm. The HOMOs, LUMOs and band gaps of the PPV derivatives of Copolymers I∼VIII were 5.30∼5.77, 3.04∼3.24, and 2.5∼2.2 eV, respectively. The multi-layered, light-emitting diodes of ITO/PEDOT/copolymers/LiF/Al exhibited turn-on voltages of 6∼2.5 V. Copolymer VIII exhibited the maximum brightness of 3,657 cd/m 2 . Particularly, Copolymer VII, with an identical composition of MEH-PPV and naphthalene-PPV, showed a maximum luminance efficiency and power efficiency of 2.63 cd/A and 1.06 lm/W, respectively.