The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs

Luminescent Iridium Complexes Used in Light-Emitting Electrochemical Cells (LEECs)

“…Entry 1 effectively demonstrates this principle with the device based on 1 exhibiting a remarkably long lifetime of 668 h. The authors attribute this stability to the relatively large calculated 3 MC-T 1 energy gap for 1 [23]. Theory and experimental observations have implicated 3 MC states in an elongation of the N pyridyl -Ir bond of the C^N ligands of [Ir(C^N) 2 (N^N)] ? complexes, which accounts for the efficient nonradiative quenching resulting from these states [40].…”

“…complexes can also demonstrate structured emission profiles that are attributed to centered radiative decay ( 3 LC). It is not uncommon for cationic iridium complexes to exhibit emission from a mixture of 3 LC and 3 MLCT/ 3 LLCT states [3]. The photophysical properties of many iridium complexes in the solid state are very different to the solution state.…”

“…The synthesis proceeds first by isolation of the ldichloro-bridged cyclometalated iridium dimer intermediate, following refluxing an iridium(III) salt in high boiling alcoholic solvents such as 2-ethoxyethanol, as first demonstrated by Nonoyama in 1974 [10]. Although Nonoyama demonstrated this synthesis using Na 3 [IrCl 6 ] as the iridium source, IrCl 3 .nH 2 O is now by far the most popular source of iridium used for synthesizing these complexes. The dimer can then be easily cleaved in the presence of a neutral N^N ligand under mild conditions (such as refluxing DCM/methanol) [11], with the complex isolated as its chloride salt.…”

“…Alternatively, the Baranoff group has explored using iridium(I) precursor materials in lieu of the more conventional iridium(III) chloride salts. Often, iridium dimers isolated from the IrCl 3 .nH 2 O reaction are not pure, but are nevertheless used without purification in the subsequent cleavage step. Purification of the final complex usually involves chromatography and/or recrystallization.…”

“…Since the first report of a phosphorescent emitter in an organic light-emitting diode (OLED) [1], iridium complexes have come to be the most widely used class of emitters employed for this purpose by virtue of their efficient spin-orbit coupling (SOC) processes that relax the spin selection rule that otherwise forbids T 1 to S 0 transitions [2][3][4]. In an electroluminescent device, spin statistics necessitates that 75 % of excitons generated in the device are in the triplet state, while the remainder are in the singlet state.…”