Sublimation Not an Innocent Technique: A Case of Bis-Cyclometalated Iridium Emitter for OLED

Isomerization of a neutral bis-cyclometalated Ir(III) complex was obsd. for the 1st time during the prepn. of vacuum-processed org. light-emitting devices (OLEDs) and reproduced in soln. Isolation of the isomer revealed a cis organization of the 2 pyridine rings of the cyclometalating ligands. Photophys. studies show very similar emission properties of the 2 isomers. However, due to in situ isomerization, it is only possible to prep. vacuum-processed OLED devices having a mixt. of isomers.