Blue Organic Electrophosphorescence Using Exothermic Host–Guest Energy Transfer

The authors demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of N,N dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C] 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 N, N dicarbazolyl-4 biphenyl and FIrpic system. The design of an efficient, electrophosphorescent organic lightemitting device often begins with the selection of a materials combination that allows for exothermic energy transfer between conductive host and phosphorescent guest molecules. The authors have demonstrated efficient blue electrophosphorescence by employing an emissive exothermic host guest material system consisting of mCP and FIrpic. The favorable relative energies of the triplet states of these two materials leads to improved host guest energy transfer, allowing for significant increases in device performance over structures employing the endothermic host guest pair of CBP and FIrpic.