Nanosecond transient absorption and time-resolved spectroscopic techniques were applied to study an organometallic phosphorescent emitter Ir(ppy)3 complex, tris[2-phenylpyridinato-C2,N] iridium(III) dissolved in tetrahydrofuran (THF) under degassed conditions at ambient temperature. Transient absorption curves obtained at a pump pulse of 355 nm and at a probe wavelength of 430–600 nm show positive and negative signals, indicating triplet–triplet (T–T) absorption and triplet–singlet (T–S) emission. Tri-exponential global fitted transient absorption curves and time-resolved photoluminescence (PL) decays demonstrated the presence of four close low lying triplet states, of which, two emit green PL with a lifetime of 210 ns and 1.71 μs. The emitting states are spin mixed metal-to-ligand charge transfer (3MLCT) states produced from a non-equilibrium 1MLCT state following fast intersystem crossing (ISC), whereas the 1MLCT state is produced directly and indirectly depending on the excitation wavelength. Moreover, the electronic structures for the ground state and low-lying excited states of Ir(ppy)3 were studied using quantum chemistry calculations.
