posted on 2024-01-19, 17:49authored byChia Chun Wu, Yu-Xiang Tsai, Li-Kang Chu, I-Chia Chen
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 T3 ← T1 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 T7 ← T1, T6 ← T1, and T6 ← T1 transitions, respectively.
For Ir(ppy)3, the most intense band involved transitions
between different triplet metal-to-ligand charge transfer (3MLCT) states, while for Ir(piq)3 and FIrpic, they involved
a metal center to 3MLCT transition. These T1 states were assigned to 3MLCT.