Interactions of low-energy electrons with Ir(ppy)3 in the gas phase

The relative efficiency of excitation into singlet and triplet states in the region between 1.5 and 9 eV, their dependence on projectile electron energies for the scattering of monoenergetic electrons with tunable energies from 0 to 50 eV at an angle of 900, for the widely known electroactive organic material tris(2-phenylpyridine)iridium (Ir(ppy)(3)) in the gas phase are presented. Some direct singlet-triplet transitions in the region 2.5-2.8 eV and nearby 4.4 eV are observed. No intense singlet-triplet transitions can be observed in spite the presence of the heavy Ir atom; this is probably due to the charge transfer nature of the transition. The spectrum of singlet and the positions of triplet transitions are studied using density functional theory techniques. No essential differences between optical and electron impact excitation of Ir(ppy)(3) have been found, and phosphorescence can be observed mainly owing to intercombination singlet-triplet transitions. (c) 2006 Elsevier B.V. All rights reserved.