Abstract
Triplet transitions of light-emitting materials, including rose bengal, tris(2-phenylpyridine)iridium(III) [Ir(ppy)(3)], tris(1-phenylisoquinoline)iridium(III) [Ir(piq)(3)], and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic), were studied using step-scan time-resolved Fourier-transform near-infrared spectroscopy. The samples were excited to their singlet excited states by a 355 nm laser and then underwent efficient conversions/crossings to their triplet manifolds. For rose bengal, a transient absorption band appeared at 9400 cm(-1), attributed to the T(3) ← T(1) transition based on the corresponding time evolution and the theoretical calculations. For Ir(ppy)(3), Ir(piq)(3), and FIrpic, the most intense bands were observed at 7700, 7500, and 7500 cm(-1) and assigned to T(7) ← T(1), T(6) ← T(1), and T(6) ← T(1) transitions, respectively. For Ir(ppy)(3), the most intense band involved transitions between different triplet metal-to-ligand charge transfer ((3)MLCT) states, while for Ir(piq)(3) and FIrpic, they involved a metal center to (3)MLCT transition. These T(1) states were assigned to (3)MLCT.