Studies of efficient heteroleptic Ir(III) complexes containing tpy and dfppy ligands for phosphorescent organic light-emitting devices.

To increase the luminescent efficiency by avoiding T-T annihilation and reducing the number of luminescent ligands, we designed and synthesized Ir(dfppy)(tpy)2 and Ir(dfppy)2(tpy), where dfppy and tpy represent 2,4-difluoro-phenylpyridine and 2-(p-tolyl)pyridine. The emission wavelength of Ir(dfppy)(tpy)2 and Ir(dfppy)2(tpy) are observed at 494 and 490 nm, respectively. The luminescence mechanism in the heteroleptic iridium complex determined the decay rates and the triplet energy between two different ligands. To confirm the color tuning by the substitution, we have measured UV-absorption and photoluminescence (PL) spectra. In addition, to predict the energy level of the iridium complex, we calculated these complexes theoretically by the density functional theory (DFT) methods.