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

Abstract

Isomerization of a neutral bis-cyclometalated iridium(III) complex has been observed for the first time during the preparation of vacuum-processed organic light-emitting devices (OLEDs) and reproduced in solution. Isolation of the isomer revealed a cis organization of the two pyridine rings of the cyclometalating ligands. Photophysical studies show very similar emission properties of the two isomers. However, due to in situ isomerization, it is only possible to prepare vacuum-processed OLED devices having a mixture of isomers.

Investigation of FIrpic in PhOLEDs via LC/MS technique

“…These findings were similar to the report from Baranoff et al using (Ir(2-phenylpyridine)2(2-carboxy-4-dimethyl amino pyridine)) [22]. Pure sublimated FIrpic material did show only one signal whereas in device manufacture a mixture of isomers from the light blue emitting material FIrpic could be detected.…”

“…Very recently, isomerization of heteroleptic iridium complexes such as from (Ir(2-phenylpyridine)2(2-carboxy-4-dimethyl amino pyridine)) and iridium(III) bis(4,6-difluorophenyl)-pyridinato-N,C2')picolinate (FIrpic) during sublimation process was reported [22].…”

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…[36] While the structure of bis-cyclometallated complexes synthesized via chloro-bridged precursors is usually predetermined, Baranoff et al observed partial thermal isomerization of a picolinate complex during vacuum sublimation. [37] The isomerization could be reproduced in solution upon thermal treatment, in a process analogous to the reported mer-fac isomerization of tris-cyclometallated Ir III complexes. While refluxing in glycerol for 20 h resulted in 40% of the new isomer, the attempt to induce the isomerization by irradiation (i.e., UV and visible light) was not successful.…”

Fluorine cleavage of the light blue heteroleptic triplet emitter FIrpic

“…Homoleptic d 6 transitions Ir(III) complexes have only the fac and mer isomers, whereas in heteroleptic systems four different isomers are possible [20]. At first the nonsublimated and sublimated FIrpic materials were analyzed using a specially developed HPLC method, which is able to separate the different isomers.…”