Daobo Nie

Acetonitrile-vapor-induced color and luminescence changes in a cyclometalated heteroleptic iridium complex.

An iridium complex PIr(qnx) (iridium(III) bis(2-phenylpyridinato-N,C(2))(quinoxaline-2-carboxylate)) is reported for its unique and fast vapochromic and vapoluminescent behaviors. The emission of PIr(qnx) is governed by the whole crystal rather than the individual molecule. PIr(qnx) has been found to exist as both black and red forms in the solid state. The black form can be transformed into the red form upon its exposure to acetonitrile or propiononitrile vapor, whereas no response was observed when it was exposed to other volatile organic compounds. To understand the vapochromic and vapoluminescent behaviors, we determined crystal structures of both forms by X-ray diffraction. In addition, we employed density functional theory in investigating weak intermolecular interactions, such as hydrogen bonding and pi-pi interactions in the two forms.

Promoting near-infrared emission of neodymium complexes by tuning the singlet and triplet energy levels of β-diketonates

A series of neodymium complexes with various modified β-diketonates and their corresponding gadolinium complexes have been synthesized and characterized. The singlet and triplet energy levels of the coordinated ligands were measured and compared. These complexes emit characteristic Nd3+ light at about 880, 1060, 1330 nm with long-lived lifetimes. The relationship between the structure and photophysical properties has been discussed and the energy transfer process in these complexes has been studied.

Energy transfer pathways in the carbazole functionalized β-diketonate europium complexes

Two novel Eu3+ complexes Eu(CDBM)3·2H2O and Eu(CCDBM)3·2H2O have been synthesized (CDBM = 1-(4-(9-carbazol)phenyl)-3-phenyl-1,3-propanedione, CCDBM = 1-((4-(9-carbazol)methyl)phenyl)-3-phenyl-1,3-propanedione). Eu(CDBM)3·2H2O showed strong internal ligand charge transfer (ILCT) fluorescence and sensitized emission of Eu3+. Due to the charge transfer character, the fluorescence band of CDBM shifted from 403 nm in cyclohexane to 559 nm in acetonitrile. Photophysical studies demonstrated that no energy was migrated from the ILCT excited state of the ligands to Eu3+, and that Eu3+ was sensitized by the triplet state which was localized in the 1,3-diphenyl-1,3-propanedione (DBM) part. The quantum efficiencies of Eu3+ in the three complexes are in the order Eu(DBM)3·2H2O > Eu(CCDBM)3·2H2O > Eu(CDBM)3·2H2O in both solution and the solid state. The energy transfer pathways in the three Eu3+ complexes were discussed in detail. Based on the systematic photophysical studies, a new guideline for the organo-lanthanide light emitting materials has been proposed: ILCT should be avoided during molecular modification.

Photophysical Properties of Heteroleptic Iridium Complexes Containing Carbazole-Functionalized β-Diketonates

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.

Sensitised near-infrared emission from lanthanides using an iridium complex as a ligand in heteronuclear Ir2Ln arrays

The iridium(III) complex Ir(ppy)2(phen5f) [ppy = 2-phenylpyridinato-N,C2′, and phen5f = 4,4,5,5,5-pentafluoro-1-(1′,10′-phenanthrolin-2′-yl)-pentane-1,3-dionate] has been synthesised and used as “complex ligands” to make heteronuclear d–f complexes by the attachment of Ln(NO3)3·xH2O at the vacant coordination sites in the bridging ligand phen5f. The microanalyses and crystal structure characteristics confirmed the formation of the heteronuclear Ir2Ln arrays. The measurement of the lowest triplet state energy level of Ir(ppy)2(phen5f) indicates that it is suitable for the NIR (near-infrared) lanthanide ions, NdIII, YbIIIand ErIII. Upon irradiation of the MLCT (metal-to-ligand charge transfer) absorption of Ir(ppy)2(phen5f) at an excitation wavelength from 380–490 nm, the characteristic emission spectra of the three Ir2Ln arrays (Ln = Nd, Yb, Er) in both the solid state and in CH3CN solution were measured. According to the results, more IrIII complexes will be designed for lanthanide NIR emission by the proper combination between the cyclometalated ligand and the tetradentate ancillary ligand.