Energy‐transfer dynamics of blue‐phosphorescent iridium and rhodium complexes doped in fluorescent molecules

Abstract

Abstract— The temperature‐dependent photoluminescence features of polycarbonate thin films doped with blue‐phosphorescent molecules, either bis[(4,6‐difluorophenyl)‐pyridinato‐N,C2′] (picolinate) iridium (Flrpic) or bis(2‐phenylpyridinato‐N,C2′) (acetylacetonate) rhodium [(ppy)2Rh(acac)], which have an equivalent triplet energy of 2.64 eV, have been studied. The photoluminescence intensity of the Flrpic‐doped polycarbonate thin film did not show any dependence on temperature. On the other hand, as for the (ppy)2Rh(acac)‐doped polycarbonate thin film, decreasing photoluminescence intensity with increasing temperature (especially above 100K) was clearly visible. These results reflect that the internal heavy‐atom effect of (ppy)2Rh(acac) is weaker than that of Flrpic. Furthermore, the steady‐state and time‐resolved photoluminescence spectra of tris(8‐hydroxyquinoline) aluminum (Alq3) thin films heavily doped with Flrpic or (ppy)2Rh(acac) (50 wt.%) at 8K was studied. It was found that the enhanced phosphorescence from Alq3 is mainly due not to the external heavy‐atom effect by doping with the phosphorescent molecule but to the exothermic triplet energy transfer from the phosphorescent molecule to Alq3.