Optoelectronic properties of new functionalized heteroleptic iridium complex

Abstract

A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline (1-piq) and a functionalized β-diketone (G1), Ir(1-piq)₂G1, was synthesized and characterized by ¹H-NMR, mass spectrometry and elemental analysis. The larger conjugation of the replacement of acetylacetone (acac) by a functionalized β-diketonate ligand led to a significant decrease in the HOMO level toward vacuum level, while Ir(1-piq)₂G1 and Ir(1-piq)₂(acac) showed red phosphorescent emissions of about 620 nm in dichloromethane solution. The phosphorescent polymer light-emitting devices were achieved, with the complexes incorporated with polyfluorene (PFO) as a host polymer doped with 30% of 5-(4-biphenylyl)-2-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as electron transport material. The energy transfer mechanism of the devices was also discussed. The lower EL performance of Ir(1-piq)₂G1 is ascribed to the inter-ligand energy transfer, indicating that it is important to control the energy level of the cyclometalated and ancillary ligands.

Keywords

iridium complex / phosphorescence / energy transfer / ancillary ligands

References

[1] BaldoM. A., LamanskyS., BurrowsP. E., ThompsonM. E., ForrestS. R.. Very high-efficiency green organic light-emitting devices based on electrophosphorescence [J]. Appl Phys Lett, 1999, 75(1): 4-6

[2] HolderE., LangeveldB. M. W., SchubertU. S.. New trends in the use of transition metal-ligand complexes for applications in electroluminescent devices [J]. Adv Mater, 2005, 17(9): 1109-1121

[3] AdachiC., BaldoM. A., ThompsonM. E., ForrestS. R.. Nearly 100% internal phosphorescence efficiency in an organic light-emitting device [J]. J App1 Phys, 2001, 90(10): 5048-5051

[4] YangC. H., TaiC. C., SunI. W.. Synthesis of a high-efficiency red phosphorescent emitter for organic light-emitting diodes [J]. J Mater Chem, 2004, 14(6): 947-950

[5] LuH. P., LiuQ. D., DingJ. F., TaoY.. New triscyclometalated iridium complexes for applications in phosphorescent light-emitting diodes [J]. Synthetic Met, 2008, 158(3/4): 95-103

[6] ParkG. Y., HaY.. Red phosphorescent iridium(III) complexes containing 2,3-diphenylquinoline derivatives for OLEDs [J]. Synthetic Met, 2008, 158(3/4): 120-124

[7] SongY. H., YehS. J., ChenC. T., ChiY., LiuC. S., YuJ. K., HuY. H., ChouP. T., PengS. M., LeeG. H.. Bright and efficient, non-doped, phosphorescent organic red-light-emitting diodes [J]. Adv Funct Mater, 2004, 14(12): 1221-1226

[8] WenZ. L., HuZ. Y., LiuY., XiaoF. L., MaX. Y., ZhuM. X., ZhuW. G.. Synthesis and optophysical properties of blue-emitting iridium (III) complex bearing oxadiazole-based picolinic acid derivative [J]. J Cent South Univ Technol, 2009, 16(3): 380-384

[9] JiangC. Y., YangW., PengJ. B., XiaoS., CaoY.. High-efficiency, saturated red-phosphorescent polymer light-emitting diodes based on conjugated and non-conjugated polymers doped with an Ir complex [J]. Adv Mater, 2004, 16(5): 537-541

[10] ZhangX., ChenZ., YangC., LiZ., ZhangK., YaoH., QinJ., ChenJ., CaoY.. Highly efficient polymer light-emitting diodes using color-tunable carbazole-based iridium complexes [J]. Chem Phys Lett, 2006, 422(4/5/6): 386-390

[11] OrselliE., KottasG. S., KonradssonA. E., CoppoP., FröhlichR., De ColaL., Van DijkenA., BüchelM., BörnerH.. Blue-emitting iridium complexes with substituted 1,2,4-triazole ligands: Synthesis, photophysics, and devices [J]. Inorg Chem, 2007, 46(26): 11082-11093

[12] HwangF. M., ChenH. Y., ChenP. S., LiuC. S., ChiY., ShuC. F., WuF. L., ChouP. T., PengS. M., LeeG. H.. Iridium(III) complexes with orthometalated quinoxaline ligands: Subtle tuning of emission to the saturated red color [J]. Inorg Chem, 2005, 44(5): 1344-1353

[13] CoppoP., PlummerE., De ColaL.. Tuning iridium(III) phenylpyridine complexes in the “almost blue” region [J]. Chem Commun, 2004, 15: 1774-1775

[14] LoS. C., MaleN., MarkhamJ. P. J., MagennisS. W., BurnP. L., SalataO. V., SamuelI. D. W.. Green phosphorescent dendrimer for light-emitting diodes [J]. Adv Mater, 2002, 14(13/14): 975-979

[15] BurnP. L., LoS. C., SamuelI. D. W.. The development of light-emitting dendrimers for displays [J]. Adv Mater, 2007, 19(13): 1675-1688

[16] ZhouG., WongW. Y., YaoB., XieZ., WangL.. Triphenylamine-dendronized pure red iridium phosphors with superior OLED efficiency/color purity trade-offs [J]. Angew Chem Int Ed Engl, 2007, 46(7): 1149-1151

[17] LiangB., WangL., ZhuX. H., PengJ. B., CaoY.. Application of heteroleptic iridium complexes with fluorenyl-modified 1-phenylisoquinoline ligand for high-efficiency red polymer light-emitting devices [J]. J Organomet Chem, 2009, 694(19): 3172-3178

[18] LiangB., JiangC. Y., ChenZ., ZhangX. J., ShiH. H., CaoY.. New iridium complex as high-efficiency red phosphorescent emitter in polymer light-emitting devices [J]. J Mater Chem, 2006, 16(3): 1281-1286

[19] HuZ. Y., LuoC. P., WangL., HuangF. L., ZhuK. M., WangY. F., ZhuM. X., ZhuW. G., CaoY.. Highly efficient saturated red electrophosphorescence from isoquinoline-based iridium complex containing triphenylamino units in polymer light-emitting devices [J]. Chem Phys Lett, 2007, 441(4/5/6): 277-281

[20] TsuboyamaA., IwawakiH., FurugoriM., MukaideT., KamataniJ., IgawaS., MoriyamaT., MiuraS., TakiguchiT., OkadaS., HoshinoM., UenoK.. Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode [J]. J Am Chem Soc, 2003, 125(42): 12971-12979

[21] LiangB., WangL., XuY. H., ShiH. H., CaoY.. High-efficiency red phosphorescent iridium dendrimers with charge-transporting dendrons: Synthesis and electroluminescent properties [J]. Adv Funct Mater, 2007, 17(17): 3580-3589

[22] ZhangY., ShiH. H., CaoY.. Synthesis of conjugated polyphenylene dendritic beta-diketones [J]. Chin J Chem, 2006, 24(11): 1631-1638

[23] LamanskyS., DjurovichP., MurphyD., Abdel-RazzaqF., LeeH. E., AdachiC., BurrowsP. E., ForrestS. R., ThompsonM. E.. Highly phosphorescent bis-cyclometalated iridium complexes: Synthesis, photophysical characterization, and use in organic light emitting diodes [J]. J Am Chem Soc, 2001, 123(18): 4304-4312

[24] NazeeruddinM. K., Humphry-bakerR., BernerD., RivierS., ZuppiroliL., GraetzelM.. Highly phosphorescence iridium complexes and their application in organic light-emitting devices [J]. J Am Chem Soc, 2003, 125(29): 8790-8797

[25] TamayoA. B., AlleyneB. D., DjurovichP. I., LamanskyS., TsybaI., HoN. N., BauR., ThompsonM. E.. Synthesis and characterization of facial and meridional tris-cyclometalated iridium(III) complexes [J]. J Am Chem Soc, 2003, 125(24): 7377-7387

[26] YouY. M., ParkS. Y.. Inter-ligand energy transfer and related emission change in the cyclometalated heteroleptic iridium complex: Facile and efficient color tuning over the whole visible range by the ancillary ligand structure [J]. J Am Chem Soc, 2005, 127(36): 12438-12439