A mesogen-jacketed polymer P-Ct {poly {2,5-bis[(5-tert-butylphenyl)-1,3,4-oxadiazole] styrene}} has been investigated as a host material for IrMDPP [lr(III)bis(5-methyl-2,3-diphenylpyrazine) (acetyl acetonate)] doped polymer electrophosphorescent device. It was found that the device with P-Ct was more efficient than that with PVK. The maximum luminance and external luminous efficiency can reach 3702 cd/m(2) and 0.83 cd/A, respectively, which were higher than those of device with PVK (1999 cd/m(2) and 0.68 cd/A), which can be partly explained by the more balanced carrier injection and transportation and longer lifetime of excitons in P-Ct-TPD-IrMDPP. It was also found that as the IrMDPP content increased in P-Ct-TPD, the EL spectra color shifts from green-yellow to yellow-orange and were different from PL spectra, which was partly due to the dominating role of direct charge-trapping and recombination in the EL process over the energy-transfer routes. (c) 2007 Elsevier Ltd. All rights reserved.