Excimer Emission in Single Layer Electroluminescent Devices Based on [Ir(4,5-diphenyl-2-methylthiazolo)2(5-methyl-1,10-phenanthroline)]+ [PF6]-

A correlated photoluminescence (PL) and electroluminescence (EL) investigation of light-emitting electrochemical cells based on [Ir(4,5-diphenyl-2-methylthiazolo)(2)(5-methyl-1,10-phenanthroline)](+) [PF6](-) reveals the excimer nature of the EL emission. Excimers are formed when the device is biased and the EL emission energy is a fingerprint of the excimer intermolecular interactions induced by the local electric field at the applied voltage. Imaging measurements provide evidence that the molecular rearrangement into aggregates favors the formation of excimer states, which are irreversibly formed once the device is biased and are the preferential emitting states even in devices left unbiased for a long period of time. PL lifetime measurements in working devices provide unambiguous evidence of the excimer character of EL. These results show that excimers play a role in the mechanism of operation and performance degradation of organic light-emitting electrochemical cells (OLEC) based on ionic transition metal complexes (iTMC).