In this HOT article from Michael Grätzel and colleagues they describe how iridium based triplet emitters can be negatively affected by thermal treatments:
An inconvenient influence of iridium(III) isomer on OLED efficiency
Etienne Baranoff, Henk J. Bolink, Filippo De Angelis, Simona Fantacci, Davide Di Censo, Karim Djellab, Michael Grätzel and Md. Khaja Nazeeruddin
Dalton Trans., 2010, Advance Article
DOI: 10.1039/C0DT00414F
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