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

Abstract

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.