title: Photophysical properties of heteroleptic iridium complexes containing carbazole-functionalized beta-diketonates.
abstract: Twelve iridium complexes with general formula of Ir(C;N)(2)(LX) [C;N represents the cyclometalated ligand, i.e. 2-(2,4-difluorophenyl) pyridine (dfppy), 2-phenylpyridine (ppy), dibenzo{f, h}quinoxaline (DBQ); LX stands for beta-diketonate, i.e. acetyl acetonate (acac), 1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate (CBDK), 1-(carbazol-9-yl)-5,5,6,6,7,7,7-heptafluoroheptane-2,4-diketonate (CHFDK), 1-(N-ethyl-carbazol-3-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-diketonate (ECHFDK)] are synthesized, characterized and their photophysical properties are systemically studied. In addition, crystals of Ir(DBQ)(2)(CHFDK) and Ir(DBQ)(2)(acac) are obtained and characterized by single crystal X-ray diffraction. The choice of these iridium complexes provides an opportunity for tracing the effect of the triplet energy level of ancillary ligands on the photophysical and electrochemical behaviors. Data show that if the triplet energy level of the beta-diketonate is higher than that of the Ir(C;N)(2) fragment and there is no superposition on the state density map, strong (3)LC or (3)MLCT-based phosphorescence can be obtained. Alternatively, if the state density map of the two parts are in superposition, the (3)LC or (3)MLCT-based transition will be quenched at room temperature. Density functional theory calculations show that these complexes can be divided into two categories. The lowest excited state is mainly determined by C;N but not beta-diketonate when the difference between the triplet energy levels of the two parts is large. However, when this difference is very small, the lowest excited state will be determined by both sides. This provides a satisfactory explanation for the experimental observations.
authors.affiliation: Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P.R. China.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Liu
authors.forename: Daobo
authors.initials: D
authors.lastname: Nie
authors.forename: Zuqiang
authors.initials: Z
authors.lastname: Bian
authors.forename: Fangfang
authors.initials: F
authors.lastname: Chen
authors.forename: Bin
authors.initials: B
authors.lastname: Lou
authors.forename: Jiang
authors.initials: J
authors.lastname: Bian
authors.forename: Chunhui
authors.initials: C
authors.lastname: Huang
mesh_terms: D002227:Carbazoles / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D007495:Iridium / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D008024:Ligands; D049449:Luminescence; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010777:Photochemistry; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D002227:Carbazoles; D007659:Ketones; D008024:Ligands; D009942:Organometallic Compounds; C041514:carbazole; D007495:Iridium