Synthesis,Electrochemistry, and Photophysical Studies of Ruthenium(II) Polypyridine Complexes with D–π–A–π–D Type Ligands and Their Application Studies as Organic Memories

A new class of ruthenium(II) polypyridine complexes with a series of D–π–A–π–D type (D=donor, A=acceptor) ligands was synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry, and elemental analysis. The photophysical and electrochemical properties of the complexes were also investigated. The newly synthesized ruthenium(II) polypyridine complexes were found to exhibit two intense absorption bands at both high‐energy (λ=333–369 nm) and low‐energy (λ=520–535 nm) regions. They are assigned as intraligand (IL) π→π* transitions of the bipyridine (bpy) and π‐conjugated bpy ligands, and IL charge‐transfer (CT) transitions from the donor to the acceptor moiety with mixing of dπ(Ru^II)→π*(bpy) and dπ(Ru^II)→π*(L) MLCT characters, respectively. In addition, all complexes were demonstrated to exhibit intense red emissions at approximately λ=727–744 nm in degassed dichloromethane at 298 K or in n‐butyronitrile glass at 77 K. Nanosecond transient absorption (TA) spectroscopy has also been carried out, establishing the presence of the charge‐separated state. In order to understand the electrochemical properties of the complexes, cyclic voltammetry has also been performed. Two quasi‐reversible oxidation couples and three quasi‐reversible reduction couples were observed. One of the ruthenium(II) complexes has been utilized in the fabrication of memory devices, in which an ON/OFF current ratio of over 10⁴ was obtained.     

Highly Emissive Fused Heterocyclic Alkynylgold(III) Complexes for Multiple Color Emission Spanning from Green to Red for Solution‐Processable Organic Light‐Emitting Devices

A new class of fused heterocyclic tridentate ligand‐containing alkynylgold(III) complexes with tunable emission color has been successfully designed and synthesized. Structural modification of the σ‐donating fused heterocyclic alkynyl ligands, including substituted fluorene, carbazole, and triphenylamine, enables a large spectral shift of about 110 nm (ca. 3310 cm^?1) that covers the green to red region to be realized with the same tridentate ligand‐containing alkynylgold(III) complexes in solid‐state thin films. Interestingly, the energy of the excimeric emission can be controlled by the rational design of the fused heterocyclic alkynyl ligands. Superior solution‐processable organic light‐emitting devices (OLEDs) with high external quantum efficiencies (EQEs) of 12.2, 13.5, 9.3, and 5.2 % were obtained with green, yellow, orange, and red emission. These high EQE values are comparable to those of the vacuum‐deposited OLEDs based on structurally related alkynylgold(III) complexes.     

7-Hydroxy-2-(2,3,4-trimethoxyphenyl)-4H-1-benzopyran-4-one: (7-hydroxy-2′,3′,4′-trimethoxyflavone)

7-Hydroxy-2,3,4-trimethoxyflavone, (C₁₈H₁₆O₆),M _r =328.32 crystallizes in the orthorhombic system, space groupPbna, with the following crystal data:a=8.853(2),b=12.870(2),c=26.293(3)Å,V=2996(1)ų,Z=8, MoK, =0.67 cm^–1,D _c =1.454 g·cm^–3,F(000)=1376,T=294K. The structure was solved by direct-methods and has been refined by full-matrix least-squares methods to a finalR value (F>(F)) of 0.0496. The molecule is not planar, the dihedral angle between the phenyl ring and the fused ring system is 27.3°. There are no intramolecular hydrogen bonds, but intermolecular short hydrogen contacts exist between hydroxyl hydrogen and carbonyl oxygen atoms.     

The molecular conformation of clonidine hydrochloride,an α-adrenergic agonist

The molecular conformation of the antihypertensive drug clonidine hydrochloride [2-(2,6-dichlorophenylimino)-2-imidazole HCl] has been shown by crystallographic studies to have a nearly perpendicular arrangement of the phenyl and imidazole rings as described by the torsion angles C₂-C₁-N₁-C₂= 76 ° and C₁-N₁-C₂-N₁ = 0 °. This conformation is not either of those suggested as the minimum energy form by CNDO/2 calculations for the protonated or free-base models. However, it is consistent with a nonplanar model proposed as the active conformer based on QSAR and spectral studies. The bonding about the imidazole carbon is similar to the guanidinium ion and the three C₂-N distances of the planar imidazole ring are nearly equal. The chloride ion forms strong hydrogen bonds with the amine hydrogen (2.3 Å) and the imidazole (N₁,) hydrogen (2.4 Å). Comparison with -adrenergic agonists shows that this conformation of clonidine fits the proposed pharmacophore model and should compete effectively for the -adrenergic receptors.Presented in part at the American Crystallographic Association Meeting, Clemson, South Carolina, January 1976.     

Syntheses, characterization, and photochromic studies of spirooxazine-containing 2,2'-bipyridine ligands and their zinc(II) thiolate complexes

A series of photochromic spirooxazine-containing zinc(II) diimine bis-thiolate complexes were successfully synthesized, and their photophysical and photochromic properties were studied. The X-ray crystal structure of complex 1a has also been determined. Upon excitation by UV light at 330 nm, all the ligands and complexes exhibit photochromic behavior. The thermal bleaching kinetics of the ligands and the complexes were studied in dimethylformamide at various temperatures. The photochemical quantum yields for the photochromic reactions of the ligands and complexes were also determined.     

High internal phase emulsion templates solely stabilised by functionalised titania nanoparticles

Porous polymer foams (poly-Pickering-HIPEs) have been synthesised from stable high internal phase emulsion templates solely stabilised by low concentrations of functionalised titania nanoparticles.     

Nonionic surfactant-capped gold nanoparticles as postcolumn reagents for high-performance liquid chromatography assay of low-molecular-mass biothiols

Gold nanoparticles (GNPs) have been stabilized with nonionic surfactant ligands, i.e., Brij 35, and their aggregation could be induced rapidly and selectively by biologically active low-molecular-mass thiols including sulphydryl-containing amino acids (cysteine and homocysteine) and small peptides (glutathione, cysteinylglycine, and glutamylcysteine). A new postcolumn detection method has been developed for high-performance liquid chromatography (HPLC) assay of these small biothiols based on the analyte-induced aggregation of the GNPs. Compared with conventional thiol-reactive probes, the GNP colloids are easier to prepare, much more stable in aqueous solution over a wide pH range and at ambient temperature, and exhibit relatively high selectivity toward small biothiols. The analysis of human urine samples demonstrated that the proposed method is promising in HPLC assay of the small thiol molecules in biological fluids.