Photoionization of tris(2-phenylpyridine)iridium

The photoionization of gas-phase tris(2-phenylpyridine)iridium (Ir(ppy)(3)) has been examined. One- and two-photon studies yield a conservative estimate for the upper bound to the ionization energy of 6.4 eV. The one-photon experiment used 193nm radiation. The latter experiments used tunable UV radiation to excite the ligand-centered (LC)-L-1 state, which is followed by radiationless decay and photoionization. An accompanying paper presents a theoretical study of excited singlets and triplets and low-energy states of Ir(ppy)(3)(+). The calculated ionization energy is similar to 5.9 eV. The experimental and calculated results together indicate an ionization energy of similar to 6 eV. An undulation in the ion yield spectrum (similar to 270 cm(-1) spacing) was observed. It is due to structure in the transition that originates from T-1, which is populated through radiationless decay of (LC)-L-1. At low fluence, Ir(ppy)(3)(+) is produced without fragmentation, despite the fact that a large amount of vibrational energy is present in T-1. Specifically, this vibrational energy is the sum of hv - E-T1 and the thermal energy due to the 177 Ir(ppy)(3) vibrational degrees of freedom at 500 K, i.e. the temperature at which the experiments were carried out. This vibrational energy is transported efficiently to the cation.