Investigating photoluminescence and electroluminescence of iridium(III)-based blue-emitting phosphors

The syntheses of two new cyclometalated ligands [2-(2′,4′-difluorophenyl)-4-tert-butylpyridine (F2tBuppy) and 2-(2′,4′-difluorophenyl)-4-oxyhexylpyridine (F2HexOppy)] were carried out. Blue-light emitting iridium(III) complex dopants [Ir(F2tBuppy)2(acac/pic)] (acac = acetylacetone; pic = picolinic acid) and [Ir(F2HexOppy)2(acac/pic)] were prepared using these cyclometalated ligands with acetylacetone and picolinic acid as their ancillary ligands. The structure of the complexes, [Ir(F2tBuppy)2(acac)] and [Ir(F2tBuppy)2(pic)] were authenticated by X-ray single-crystal structure analysis and showed an octahedral geometry. Comparative absorption and emission spectra of thin-films as well as their solution samples were studied. The variation of the lowest emitting states to their corresponding unsubstituted complexes, [Ir(F2ppy)2(acac/pic)] was also discussed. The electroluminescent (EL) device was fabricated using [Ir(F2tBuppy)2(pic)] as the dopant (D-I) into the emitting layer and compared with two other EL devices where [Ir(F2MeOppy)2(acac)] (D-II) and FIrpic (D-III) dopants were used in the same device structure. The lower driving voltages obtained for D-I with respect to D-II and D-III devices were rationalized. The exceptional lowering of the luminance yield of the substituted dopants containing devices, D-I and D-II, to that of D-III which contains the unsubstituted dopant was also investigated.

Graphical abstractThe syntheses of new blue-emitting phosphorescent iridium(III) based complexes were carried out. The maximum emission wavelengths were tuned with respect to the electronic properties of the substituents. The photoluminescence behavior of picolinates versus acetylacetonates was investigated. One of the substituted complex dopants was applied in organic light emitting devices and compared with its unsubstituted analogue.Figure optionsDownload full-size imageDownload as PowerPoint slide