title: Light-Induced Structural Change in Iridium Complexes Studied by Electron Spin Resonance.
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 photodegradation 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 (ESR). Photogenerated charged states with relatively strong hyperfine interactions were observed and attributed to matrix/complex charge-transfer processes. Measurements of the signal amplitude decay after photoexcitation interruption were performed as a function of temperature. The photoinduced centers are thermally activated with energy barrier between 0.3 and 0.6 eV. Electronic structure calculations suggest that the signals observed by ESR are associated with metastable negatively charged Ir complexes distorted structures.
authors.affiliation: Campus Experimental de Itapeva, UNESP - Univ Estadual Paulista , Rua Geraldo Alckmin 519, Itapeva, São Paulo 18409-010, Brazil.
authors.forename: A
authors.initials: A
authors.lastname: Batagin-Neto
authors.affiliation: POSMAT - Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, UNESP - Univ Estadual Paulista , Bauru, São Paulo 17033-360, Brazil.
authors.forename: A P
authors.initials: AP
authors.lastname: Assis
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo , São Carlos, São Paulo 05508-070, Brazil.
authors.forename: J F
authors.initials: JF
authors.lastname: Lima
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo , São Carlos, São Paulo 05508-070, Brazil.
authors.forename: C J
authors.initials: CJ
authors.lastname: Magon
authors.affiliation: The University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: L
authors.initials: L
authors.lastname: Yan
authors.affiliation: The University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: M
authors.initials: M
authors.lastname: Shao
authors.affiliation: The University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: B
authors.initials: B
authors.lastname: Hu
authors.affiliation: DF-FC, UNESP, Univ Estadual Paulista , Avenida Eng. Luiz Edmundo Carrijo Coube, 14-01, Bauru, São Paulo, 17033-360, Brazil.
authors.forename: C F O
authors.initials: CFO
authors.lastname: Graeff