Solvation oscillations and excited-state dynamics of 2-amino- and 2-hydroxy-7-nitrofluorene and its 2'-deoxyriboside

Push-pull substituted fluorenes are considered for use as dynamic solvation probes in polynucleotides. Their fluorescence band is predicted (by simulations) to show weak spectral oscillations on the subpicosecond time scale depending on the nucleotide sequence. The oscillations reflect the local far-infrared spectrum of the environment around the probe molecule. A connection is provided by the continuum theory of polar solvation which, however, neglects molecular aspects. We examine the latter using acetonitrile solution as a test case. A collective librational solvent mode at 100 cm(-1) is observed with 2-amino-7-nitrofluorene, 2-dimethylamino-7-nitrofluorene, 2-hydroxy-7-nitrofluorene, and its 2'-deoxyriboside. Different strengths of the oscillation indicate that rotational friction of nearby acetonitrile molecules depends on the solute structure or that H bonding is involved in launching the librational coherence. Polar solvation in methanol is used for comparison. With hydroxynitrofluorenes, the observation window is limited by intersystem crossing for which rates are reported. A prominent excited-state absorption band of nitrofluorenes at 430 nm can be used to monitor polar solvation. Structural and electronic relaxation pathways are discussed with the help of quantum chemical calculations.     

Thermal properties of hafnium(IV) and zirconium(IV) β-diketonates

Five volatile hafnium(IV) and zirconium(IV) β-diketonates: hafnium(IV) acetylacetonate, hafnium(IV) trifluoroacetylacetonate, hafnium(IV) pivaloyltrifluoroacetonate, hafnium(IV) 2,2,6,6-tetramethylheptane-3,5-dionate and zirconium(IV) 2,2,6,6-tetramethylheptane-3,5-dionate were obtained, purified and identified. Thermal behavior of solid compounds was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) in helium atmosphere and in vacuum. DSC method was also used for definition of thermodynamic characteristics of melting processes. Using the static method with quartz membrane zero-manometer and the flow method the temperature dependencies of saturated vapor pressure for hafnium(IV) complexes was obtained. The standard thermodynamic characteristics ΔH _T⁰ and ΔS _T⁰ of sublimation and evaporation processes were calculated from the temperature dependences of saturated vapor pressure.     

Trans-stereoselectivity in the reaction between homophthalic anhydride and imines

The reaction between homophthalic anhydride and imines in the presence of TiCl4 and diisopropyl ethyl amine is trans-selective. Under these conditions, the reaction using homochiral imines can be highly diastereoselective, thus allowing the synthesis of enantiopure 1,2,3,4-tetrahydro-1-oxoquinoline-4-carboxylic acids.     

Zirconium phosphate/phosphonate multilayered films based on push-pull stilbazolium salt: synthesis, characterization and second harmonic generation

The preparation of materials featuring enhanced second harmonic generation (SHG) values by self-assembly of molecules characterized by high second-order non-linear optic (NLO) activity is nowadays an important and challenging field of research. In order to show SHG the material must have an acentric structure with the dipoles of the molecular components oriented in the same direction and this is synthetically fairly difficult to achieve. This study describes the synthesis of the push-pull stilbazolium salt and its assembly in multilayered acentric thin films, on quartz glass surface, by using the zirconium phosphate/phosphonate (Zr-PO(x)) technique. A particular care has been paid to the optimization of the surface preparation and of the deposition conditions. This allows to obtain highly homogeneous lamellar inorganic-organic materials showing satisfactory second harmonic generation (SHG) values together with high chemical, thermal and mechanical stabilities which are necessary for their integration in optoelectronic devices.     

Synthesis and in-vitro antitumor activity of 1-[3-(indol-1-yl)prop-1-yn-1-yl]phthalazines and related compounds

A series of novel 3-(indol-1-yl)prop-1-yn-1-yl-substituted phthalazines and related azines was prepared via a concise pathway by palladium-catalyzed cross-coupling of appropriate halo-azines and N-propargylindoles. Some of the compounds exhibited significant antitumor activity in an in-vitro assay.     

2-Amino-7-nitro-fluorenes in neat and mixed solvents-optical band shapes and solvatochromism

Femtosecond transient absorption spectroscopy of amino-nitro-fluorenes in the UV-visible range shows that the dynamic Stokes shift of the emission band is sensitive to infrared-active modes of the solvent. Bandshapes for stationary absorption and emission are needed to quantify the observed spectral evolution. They are reported for 2-amino-7-nitro-fluorene (ANF), 2-dimethylamino-7-nitro-fluorene (dM-ANF), and 2-di(n-butyl)amino-7-nitro-9-di(n-propyl)-fluorene (dBdP-ANF) in a variety of solvents. Bands broaden systematically with increasing solvent polarity. This effect is taken into account in an improved location of band positions. The resulting solvatochromic plots differ significantly from those that use peak positions of absorption spectra and fluorescence quantum distributions. Absorption spectra were also measured in aqueous solvent mixtures, and shifts are described by binding curves for hydrogen bonding and stepwise solvent exchange.     

Coding a coordination-driven self-assembly via a hydrogen bond-directed solid-state synthesis: an unexpected chiral tetrahedral capsule

An achiral ligand, synthesized in the solid state via a coded hydrogen bond-directed organic synthesis, self-assembles with Cu(II) ions to form a chiral tetrahedral capsule that hosts an anion as a guest.     

One-pot derivatization of medicinally important 9-aminoacridines by reductive amination and SNAr reaction

A new highly efficient one-pot derivatization of medicinally important 9-aminoacridines (9-AA) at the amine position is described. Simple reductive amination and S_NAr reaction using easily accessible starting materials give a fast entry to novel 9-AA derivatives for biological screening.