Blue organic electrophosphorescence using exothermic host–guest energy transfer

We demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of ${\mathrm{N,N}}^{\prime }$ -dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-${\mathrm{N,C}}^{2^{\prime }}]\mathrm{picolinate}$ (FIrpic). By examining the temperature dependence of the radiative lifetime and the photoluminescence of a film of mCP doped with FIrpic, we confirm the existence of exothermic energy transfer in contrast to the endothermic transfer characteristic of the ${\mathrm{N,N}}^{\prime }$ -dicarbazolyl-${\text{4-4}}^{\prime }$ -biphenyl and FIrpic system. In employing exothermic energy transfer between mCP and FIrpic, a maximum external electroluminescent quantum efficiency of $\text{(7.5±0.8)\%}$ and a luminous power efficiency of $\text{(8.9±0.9)}\mathrm{lm/W}$ are obtained, representing a significant increase in performance over previous endothermic blue electrophosphorescent devices.