Guest Speaker: Professor Carlos F.O. Graeff (Departamento de FísicaUniversidade Estadual Paulista Júlio de Mesquita Filho, Faculdade de Ciências de Bauru, Brasil)
Time: 2014-12-19 (Friday), 10：10 - 12：00
Location: Conference Room 7215, School of Science

Abstract

Iridium-based compounds are materials of great interest in the production of highly efficient organic light emitting diodes and several other applications. However, these organometallic compounds present relative low stability due to photo-degradation processes still not well understood. In this work we investigated paramagnetic states induced by UV photoexcitation on iridium(III) bis[(4,6-fluorophenyl)-pyridinato-N,C2’] picolinate (FIrpic) and iridium(III)-tris(2-phenylpyridine) (Ir(ppy)3) complexes  dispersed in different polymeric matrices by Electron Spin Resonance. Photo-generated charged states with relatively strong hyperfine interactions were observed attributed to matrix/complex charge-transfer processes. Measurements of the signal amplitude decay after photo-excitation interruption were performed as a function of temperature. The photo-induced centers are thermally activated with energy barrier between 0.3-0.6 eV. Electronic structure calculations suggest that the signals observed by ESR are associated to metastable negatively charged Ir complexes distorted structures.