Shie-Ming Peng

Organic light-emitting diodes based on charge-neutral Os(II) emitters: generation of saturated red emission with very high external quantum efficiency

The OLED device using 6% of Os(fptz)2(PPh2Me)2 as the dopant emitter in a CBP host and BPAPF as hole transporting material shows an external quantum efficiency of 15.3% and luminous efficiency of 21.3 cd A−1, power efficiency of 6.3 lm W−1 at 20 mA cm−2. An even higher external quantum efficiency of ∼20% was achieved at a low current density of ∼1 mA cm−2.

Highly bright blue organic light-emitting devices using spirobifluorene-cored conjugated compounds

An efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, 2,7-bis[2-(4-tert-butylphenyl)pyrimidine-5-yl]-9,9′-spirobifluorene (TBPSF), as an emitter or a host for blue organic light-emitting devices (OLEDs), is reported. The steric hindrance inherent with the molecular structure renders the material a record-high neat-film photoluminescence (PL) quantum yield of 80% as a pure blue emitter (PL peak at 430 nm) of low molecular weight, and a very high glass-transition temperature (Tg) of 195 °C. Blue OLEDs employing this compound as the emitter or the emitting host exhibit unusual endurance for high currents over 5000 mA/cm2. When TBPSF is used as a host for perylene in a blue OLED, maximal brightness of ∼80 000 cd/m2 had been achieved, representing the highest values reported for blue OLEDs under dc driving.

Self‐Assembled Arrays of Single‐Walled Metal–Organic Nanotubes

Many recent advances in the field of metal–organic framework (MOF) materials have been reported, not only from the standpoint of the potential applications, ranging from gas storage to catalysis and drug delivery, but also because of their intriguing architectures and framework topologies. 2] Conceptually, endless structures can be produced by assembling judiciously selected molecular building blocks. Just as the notable saying in crystal engineering goes “the limits are mainly in our imagination”, any conceivable MOF might be obtained in the future, although it is all currently imagination. Since the first discovery of carbon nanotubes (CNTs) by Iijima in 1991, discrete hollow tubular structures such as various CNTs and other synthetic nanotubes (SNTs) prepared from inorganic, organic, or biological precursors have been successfully developed, because they possess useful functionalities and can serve as molecular capillaries, sieves, and biological models. In theory, the curling-up or rollingup mechanism of topology transformations from 2D flat sheets to 1D hollow tubes is achievable. Thanks to effective design and synthesis strategies, many porous MOFs with various interesting network topologies have been reported over the past decade. Compared with the focus on CNTs and SNTs, it is surprising that significantly less effort has been directed to the preparation of metal–organic nanotubes (MONTs). In particular, discrete MONT structures are extremely rare to date. As part of our ongoing efforts in the design and synthesis of functional crystalline materials, 8d, 10] we wish to report herein on a unique type of MOF of [{[Cd(apab)2(H2O)]3(MOH)·G}n] (MAS-21–23, M I = Cs, K, Na, respectively; for MAS-22, G = 18 H2O·6C2H5OH·3C4H8O; apab = 4-amino-3[(pyridin-4-ylmethylene)amino]benzoate; MAS = materials of Academia Sinica), all of which consist of a large singlewalled metal–organic nanotube of [{Cd(apab)2(H2O)}3n] (MONT-A1) with an exterior wall diameter of up to 3.2 nm and an interior channel diameter of 1.4 nm. These MONTs are held together by alkaline cations to form 3D nanotubular supramolecular arrays (Figure 1). To the best of our knowledge, a single-walled MONT with such a large diameter is unprecedented. Compounds MAS-21–23 were synthesized by reaction of cadmium perchlorate, 4-amino-3-[(pyridin-4-ylmethylene)amino]benzoic acid (Hapab), and MOH (M = Cs, K, and Na, respectively) in an EtOH/THF/H2O solvent diffusion system at 4 8C through a single-step, self-organization process (Scheme 1). The appropriate choice of an organic ligand with specific functional groups and geometry is a major factor in achieving these large nanotube-based structures. The multifunctional Schiff base ligand of Hapab was designed deliberately and possesses a bending angle of 1208 between the pyridyl and carboxylate groups. Unlike similar bananashaped organic linkers, the use of the apab scaffold favors the formation of a tubular structure, rather than a spherical network.

Two Linear Undecanickel Mixed-Valence Complexes: Increasing the Size and the Scope of the Electronic Properties of Nickel Metal Strings**

The importance of one-dimensional (1D) transition-metal complexes stems from their ability to provide a fundamental understanding of metal–metal interactions and electron transport along an extended metal-atom chain (EMAC), and from the perspective of taking advantage of their specific properties for potential applications, such as molecular metal wires and switches. A series of string complexes of oligo-apyridylamino ligands ranging from 3 to 9 core metal atoms has been synthesized and characterized by Cotton s group and our group. Attempts to characterize such very long EMACs with high electron conductivity were hindered by the synthetic difficulties rapidly increasing with the size of the metal chain. We synthesized [Ni9(m9-peptea)4Cl2] ten years ago, but all attempts to characterize a longer chain of Ni atoms have, to date, been unsuccessful, owing to very low yields and to the instability of the target compound, probably because of the high flexibility of large pyridylamino ligands. Recently we developed a new family of ligands by substituting rigid and potentially redox active naphthyridine (na) groups for the pyridine (py) rings. Naphthyridinemodulated ligands stabilize nickel ions in a low oxidation state, giving rise to mixed-valent [Ni2(napy)4] 3+ units (napy= naphthyridine). Using this strategy, we obtained a series of stable, low-oxidation-state-nickel string complexes combining mixed-valency, a property important in the development of novel electronic materials, with an enhanced electron mobility, which is able to increase the conductance of molecular metal wires. We report a new tetranaphthyridyltriamine ligand, N-(2(1,8-naphthyridin-7-ylamino)-1,8-naphthyridin-7-yl)-N-(1,8naphthy-ridin-2-yl)-1,8-naphthyridine-2,7-diamine (H3tentra) and two undecanickel complexes of the deprotonated tentra trianion, [Ni11(tentra)4Cl2](PF6)4 (1) and [Ni11(tentra)4(NCS)2](PF6)4 (2). The ligand H3tentra was synthesized on the basis of Buchwald s palladium-catalyzed procedures by the crosscoupling of bis(2-chloro-1,8-naphthyridin-7-yl)amine and 2amino-1,8-naphthyridine. Undecametallic complex [Ni11(tentra)4Cl2](PF6)4 (1) was obtained by the reaction of anhydrous NiCl2 with the H3tentra ligand in an argon atmosphere employing naphthalene as solvent and tBuOK as a base to deprotonate the amine groups. The thiocyanate species (2) was obtained from 1 by an axial ligand exchange reaction. The crystal structures of 1 and 2 are shown in Figure 1 and the Supporting Information Figure 1S, respectively. Both 1 and 2 are tetracationic molecules associated each with four PF6 counterions. They crystallize in unusually large cells, with one dimension exceeding 50 . The Ni11 chain of 1 and 2 is linear and wrapped in a helical manner by four tentra trianions. In both complexes, the atoms of the axial ligands are collinear with the Ni11 axis; the molecular lengths are 27.7 and 32.4 for 1 and 2, respectively. These are the longest EMAC complexes reported to date. The nature of the axial ligand does not significantly affect the metal–metal bond length, and no obvious structural change is observed for compound 2 with respect to 1. Therefore, we will only analyze the structure of 1 in detail. Selected bond lengths for 1 are displayed in Figure 1c together with the corresponding values obtained from geometry optimization at the DFT/B3LYP level. Molecule 1 consists of eleven nickel atoms in a linear chain with the Ni-Ni-Ni bond angles in the range of 179–1808. The N-Ni-Ni-N torsion angles for adjacent nickel are between 13.0 and 18.78, much smaller than those in oligo-a-pyridylamino ligand EMAC complexes (ca. 22.58). Metal–metal distances usually decrease from the end to the center of the chain in both nickel and cobalt EMACs of oligo-a-pyridyl[*] Dr. R. H. Ismayilov, Dr. W.-Z. Wang, Dr. G.-H. Lee, S.-A. Hua, Prof. Dr. S.-M. Peng Department of Chemistry, National Taiwan University 1, Sec. 4, Roosevelt Road, Taipei, 106 (Taiwan, ROC) Fax: (+886)2-8369-3765 E-mail: smpeng@ntu.edu.tw

Structure of a linear unsymmetrical trinuclear cobalt(II) complex with a localized COII–COII bond: dichlorotetrakis[µ3-bis(2-pyridyl)amido]tricobalt(II)

The synthesis and X-ray crystal structure of a linear unsymmetrical trinuclear cobalt(II) complex with a syn–syn bis(2-pyridyl)amido ligand, possessing a short, localized CoII–CoII bond and a spin crossover square-pyramidal CoII ion, is described.

Photoluminescent cyclometallated diplatinum(II,II) complexes: photophysical properties and crystal structures of [PtL(PPh3)]ClO4 and [Pt2L2(µ-dppm)][ClO4]2(HL = 6-phenyl-2,2′-bipyridine, dppm = Ph2PCH2PPh2)

The complexes [PtL(Cl)]1, [PtL(PPh3)]ClO42 and [Pt2L2(µ-dppm)][ClO4]23(HL = 6-phenyl-2,2′-bipyridine, dppm = Ph2PCH2PPh2) have been prepared and their spectroscopic and emission properties studied. Complex 3 shows a broad and intense absorption at 420–510 nm which is tentatively assigned to a metal–metal to ligand charge-transfer transition 1m.m.l.c.t. 1[dσ*→σ(π*)], where dσ* arises from the antisymmetric combination of the two platinum dz2 orbitals and σ(π*) from the symmetric combination of π* orbitals of the two L ligands. All the complexes show luminescence in both the solid state and in solution. Both 1 and 2 display 3m.l.c.t. emission in solution at room temperature. The solid-state emission of 1 and both the solid-state and fluid-state emission of 3 are assigned to the 3m.m.l.c.t. 3[(dσ*){σ(π*)}] state. The crystal structure of 2 shows an intermolecular π–π interaction between two L ligands as evidenced by the intermolecular ligand plane separation of 3.35 A. The solid-state emission of 2 is suggested to arise from a π–π excimeric interaction of the L ligands. The crystal structure of 3 shows discrete [Pt2L2(µ-dppm)]2+ units with an intramolecular Pt–Pt separation of 3.2703 A.

Acid/Base‐ and Anion‐Controllable Organogels Formed From a Urea‐Based Molecular Switch

Low-molecular-weight organogels have applications in several fields, including molecular sensing, nanostructure assembly, and drug delivery. Ideally, these materials would switch reversibly between their solution and gel states through the addition or removal of heat, electrons, or ions. Although these modes of operation are similar to those employed for switches based on interlocked molecules, organogels formed from pseudorotaxaneor rotaxane-type gelators are rare. Indeed, we are aware of only a few previously reported examples, all of which feature long alkyl chains or cholesterol units incorporated into the molecular structures to assist the gelation process. Predicting the molecular structures of potential gelators and their preferred solvents remains difficult, and developing new rotaxane-based gelators that do not feature commonly used types of gelation units (e.g., long alkyl chains, steroids) in their structures is particularly challenging. Herein we report the serendipitous discovery of a urea-based [2]rotaxane that behaves as both a molecular switch and an organogelator; both functions are mediated by acid/base and anion control. The reaction of the macrocycle 1, the amino-terminated salt [2-H][PF6], [7] and the isocyanate 3 in CH3NO2 gave the dumbbell-shaped salt [4-H][PF6] and the [2]rotaxane [5-H][PF6] in 49 and 46% yield, respectively (Scheme 1). The binding constant for the assembly formed from the macrocycle 1 and dibenzylammonium hexafluorophosphate ((DBA)PF6) in CD3NO2 is (300 30)m , and 1 interacts only negligibly with diphenylurea derivatives in this solvent. 8] Therefore we suspected that the interlocked macrocycle in the [2]rotaxane [5-H][PF6] would prefer to encircle the DBA station, rather than the diphenylurea station, when dissolved in CD3NO2. Indeed, the 2D NOESY spectrum of the [2]rotaxane [5-H][PF6] in CD3NO2 shows cross-signals between the ethylene glycol protons of the macrocyclic unit and the aromatic protons of the 3,5-di-tert-butylphenyl stopper adjacent to the DBA center, however, no crosssignals are seen between the macrocyle and the stopper unit adjacent to the urea station. As expected, addition of potassium tert-butoxide (1 equivalent) to a solution of the [2]rotaxane [5-H][PF6] (CD3NO2, 13.6 mm) resulted in significant shifts in the locations of many of the signals in the H NMR spectrum (Figure 1). The significant downfield shift of the signal for the macrocyle NH protons, and the appearance of signals for the formerly severely broadened urea protons suggested the formation of hydrogen bonds to the carbonyl group of the urea station (Figure 1b). The addition of perchloric acid (70% in H2O, 1 equivalent) to this solution afforded a spectrum similar to that of the original [2]rotaxane. These observations suggest that the [2]rotaxane [5-H][X] is an acid/base-controllable molecular switch; the interlocked macrocyclic unit can be Scheme 1. Synthesis and switching of the [2]rotaxane [5-H][PF6].

A Molecular Cage-Based [2]Rotaxane That Behaves as a Molecular Muscle

We report a molecular cage-based [2]rotaxane that functions as an artificial molecular muscle through the control of the addition and removal of fluoride anions. The percentage change in molecular length of the [2]rotaxane is about 36% between the stretched and contracted states, which is larger than the percentage change (approximately 27%) in human muscle.

SELF-ASSEMBLY OF PREDESIGNED TRIMETALLIC MACROCYCLES BASED ON BENZIMIDAZOLE AS NONLINEAR BRIDGING MOTIFS : CRYSTAL STRUCTURE OF A LUMINESCENT PLATINUM (II) CYCLIC TRIMER

A trimetallic macrocycle: Starting from nonlinear N-deprotonated benzimidazole and square-planar cyclometalated platinum(II) precursors, cyclic trimers with three metal vertices can be obtained by a general and rational strategy (shown schematically, M=Pt). A complex is formed with 2-(2-thienyl)pyridine as chelating ligand which photoluminesces in solution at room temperature.

Luminescent gold(I) acetylide complexes. Photophysical and photoredox properties and crystal structure of [{Au(CCPh)}2(µ-Ph2PCH2CH2PPh2)]

The spectroscopic and photophysical properties of three gold(I)-acetylide complexes [N(PPh3)2]-[Au(CCPh)2], [Au(PPh3)(CCPh)] and [{Au(CCPh)}2(µ-dppe)][dppe = 1,2-bis(diphenyl-phosphino)ethane] are described. X-Ray crystal analysis of the latter showed a weak metal–metal interaction in the solid state with the shortest Au ⋯ Au separation being 3.153(2)A. The gold(I)–acetylide complexes have long-lived and emissive 3(π,π*) excited states in solutions at room temperature. The photoreaction of [Au(PPh3)(CCPh)] with methyl viologen has been investigated by Stern–Volmer quenching and flash-photolysis experiments.