Efficient blue electrophosphorescence was achieved from iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2′]picolinate (FIrpic) covalently bonded to the carbazole-based wide-band-gap polymer host (poly(9-dodecyl-3-vinylcarbazole); CP0). Number-average molecular weights of CP0-based copolymers containing FIrpic pendants (CP n) ranged over 18 000-33 700 when the molar content of FIrpic-containing monomer units was 0.8-10.6%: CP1 (0.8%), CP 2 (2.9%), CP3 (5.3%), and CP4 (10.6%). Phase segregation in the CPn copolymer was significantly suppressed compared to that in the doped analogues (molecular composite of CPo/FIrpic). The photoluminescence spectra of the carbazole-based polymer host (CP 0) overlapped with the absorption band of FIrpic, and the T 1 level of CP0 (-2.6 eV) was higher than that of FIrpic (-3.1 eV), ensuring highly efficient exothermic energy transfer. Electroluminescence (EL) devices employing CPn polymers as emitting layer showed exclusive FIrpic-emission due to the efficient energy transfer and subsequent exciton confinement in FIpic. The luminance of preliminary EL devices reached as high as 1450 cd/m2 with emission efficiency of 2.23 cd/A. It was specifically noted that the roll-off of external quantum efficiency in the region of high current density was interestingly suppressed in the CPn polymer devices.
|Number of pages||8|
|State||Published - 10 Jan 2006|