Highly efficient fluorene-based UV-blue light-emitting polymers with controlled effective conjugation length

POLY 664

Xing-Hua Zhou, xhzhou@u.washigton.edu1, Fei Huang2, Yu-Hua Niu2, Michelle S. Liu, shiliu@u.washington.edu2, and Alex K Y. Jen, ajen@u.washington.edu2. (1) Department of Materials Science and Engineering, Univerisity of Washington, 302 Roberts Hall, Box 352120, Seattle, WA 98195, (2) Department of Materials Science & Engineering, University of Washington, 302 Roberts Hall Box 352120, Seattle, WA 98195-2120
A series of fluorene-based light-emitting alternating copolymers is synthesized by Suzuki coupling reaction. The incorporation of d-O or d-Si interrupted and sterically hindered structures into polymer backbone could properly control the extended Π-conjugation and significantly reduce self-aggregation of polymer chains for achieving pure and efficient UV-blue emission. These polymers possess relatively high glass transition temperature (Tg ≥ 135 oC) and very good thermal stability. The photophysical studies show that this class of polymers has a large band gap of 3.143.32 eV, and exhibits an efficient UV-blue emission with λmax in the range of 395410 nm and narrow full width half-maximum. The light-emitting devices using these polymers as emitting layer yield an efficient ultraviolet-blue electroluminescence (EL) emission peaking at around 400 nm without any of the commonly observed red-shifted emission in polyfluorenes. A maximum external quantum efficiency of 1.59%, and a maximum irradiance power density of 1,161 W/cm2 as well as a low turn-on voltage of 5.2 V are demonstrated.