Comparative X-ray standing wave analysis of metal-phosphonate multilayer films of dodecane and porphyrin molecular square

The nanoscale structures of multilayer metal-phosphonate thin films prepared via a layer-by-layer assembly process using Zr(4+) and 1,12-dodecanediylbis(phosphonic acid) (DDBPA) or porphyrin square bis(phosphonic acid) (PSBPA) were studied using specular X-ray reflectivity (XRR), X-ray fluorescence, and long-period X-ray standing wave (XSW) analysis. The films were prepared in 1, 2, 3, 4, 6, and 8 layer series on both Si(001) substrates for XRR and on 18.6 nm period Si/Mo layered-synthetic microstructure X-ray mirrors for XSW. After functionalizing the SiO(2) substrate surfaces with a monolayer film terminated with phosphonate groups, the organic multilayer films were assembled by alternating immersions in (a) aqueous solutions containing Zr(4+)or Hf(4+) (final metal layer only) cations and then (b) organic solvent solutions of PO(3)-R-PO(3)(4-), where R was DDBPA or PSBPA spacer molecule. The Hf(4+) cation served as the marker for the top surface of the films, whereas the Zr(4+) cation was present in all other layers. The PSBPA also contained Zn and Re atoms at its midline which served as heavy-atom markers for each layer. The long-period XSW generated by the 0th- (total external reflection) through 4th-order Bragg diffraction conditions made it possible to examine the Fourier transforms of the fluorescent atom distributions over a much larger q(z) range in reciprocal space which permitted simultaneous analysis of Hf, Zn/Re, and Zr atomic distributions.     

Direct observation of cations and polynucleotides explains polyion adsorption to like-charged surfaces

We show an experimental approach for directly observing the condensation of polynucleotides and their electrolyte counterions at a liquid/solid interface. X-ray standing waves (XSW) generated by Bragg diffraction from a d = 20 nm Si/Mo multilayer substrate are used to measure the distinct distribution profiles of the polyanions and simple cations along the surface normal direction with subnanometer resolution. The 1D spatial sensitivity of this approach is enhanced by observing the XSW induced fluorescence modulations over multiple orders of Bragg peaks. We study the interesting divalent cation driven adsorption of anionic polynucleotides to anionic surfaces by exposing a hydroxyl-terminated silica surface to an aqueous solution with ZnCl2 and mercurated poly-uridylic acid (a synthetic RNA molecule). The in situ long-period XSW measurements are used to follow the evolution of both the Zn and Hg distribution profiles during the adsorption process. The conditions and physical mechanisms that govern the observed divalent cation adsorption and subsequent polynucleotide adsorption to an anionic surface are explained by a thermodynamic model that incorporates nonlinear electrostatic effects.     

A novel fluorescent sensor for metal cations and protons based of bis-1,8-naphthalimide

A newly synthesized bis-1,8-naphthalimide aimed to increase its fluorescence intensity in the presence of protons or metal cations has been investigated. Its spectral photophysical characteristics in acetonitrile and chloroform solutions are described. The influence of metal cations (Zn(2+), Ni(2+), Ce(3+), Co(2+), Cu(2+) and Ag(+)) and protons on the fluorescence intensity has been investigate with regard to obtain fluorescence sensors for this ions in the environment.     

X-ray studies of self-assembled organic monolayers grown on hydrogen-terminated Si(111)

The structure of self-assembled monolayers (SAMs) of undecylenic acid methyl ester (SAM-1) and undec-10-enoic acid 2-bromo-ethyl ester (SAM-2) grown on hydrogen-passivated Si(111) were studied by X-ray reflectivity (XRR), X-ray standing waves (XSW), X-ray fluorescence (XRF), atomic force microscopy, and X-ray photoelectron spectroscopy (XPS). The two different SAMs were grown by immersion of H-Si(111) substrates into the two different concentrated esters. UV irradiation during immersion was used to create Si dangling bond sites that act as initiators of the surface free-radical addition process that leads to film growth. The XRR structural analysis reveals that the molecules of SAM-1 and SAM-2 respectively have area densities corresponding to 50% and 57% of the density of Si(111) surface dangling bonds and produce films with less than 4 angstroms root-mean-square roughness that have layer thicknesses of 12.2 and 13.2 angstroms. Considering the molecular lengths, these thicknesses correspond to a 38 degrees and 23 degrees tilt angle for the respective molecules. For SAM-2/Si(111) samples, XRF analysis reveals a 0.58 monolayer (ML) Br total coverage. Single-crystal Bragg diffraction XSW analysis reveals (unexpectedly) that 0.48 ML of these Br atoms are at a Si(111) lattice position height that is identical to the T1 site that was previously found by XSW analysis for Br adsorbed onto Si(111) from a methanol solution and from ultrahigh vacuum. From the combined XPS, XRR, XRF, and XSW evidence, it is concluded that Br abstraction by reactive surface dangling bonds competes with olefin addition to the surface.     

Synthesis, structural characterization, experimental, and computational spectrophotometric studies of 8-quinolinyloxymethyphosphonate compounds

The synthesis of diethyl-8-quinolinyloxymethylphosphonate 1 and 8-quinolinyloxymethylphosphonic acid hemihydroiodide 2 is reported along with their spectroscopic and analytical characteristics (NMR, infrared, mass spectra, and elemental analysis). The single-crystal X-ray structure of 2 is described. Solutions of the disodium phosphonate 3, from 2 and sodium hydroxide, were prepared and used in situ. The coordination complex between 1 and zinc chloride 4 is described according to its single-crystal X-ray structure. The spectrophotometric features (absorption and emission) of 1, 2, 3, and 4 are reported along with the fluorescence response and affinity of 3 to some metal cations. The origin of the fluorescence from compounds 1 and 4 is investigated using density functional theory and the oscillator strength for each transition is computed. Two deactivation pathways, one of which is only weakly emissive, are identified in 4. In contrast to 4, which is only moderately more emissive than 1 a strong zinc-activated fluorescence response is observed from aqueous solutions of 3.     

Solid-state chelation of metal ions by ethylenediaminetetraacetate intercalated in a layered double hydroxide

The solid-state chelation of transition metal ions (Co(2+), Ni(2+), and Cu(2+)) from aqueous solutions into the lithium aluminum layered double hydroxide ([LiAl(2)(OH)(6)]Cl x 0.5H(2)O or LDH) which has been pre-intercalated with EDTA (ethylenediaminetetraacetate) ligand has been investigated. The intercalated metal cations form [M(edta)](2)(-) complexes between the LDH layers as indicated by elemental analysis, powder X-ray diffraction, and IR and UV-vis spectroscopies. If metal chloride or nitrate salts are used in the reaction with the LDH then co-intercalation of either the Cl(-) or NO(3)(-) anions is observed. In the case of metal acetate salts the cations intercalate without the accompanying anion. This can be explained by the different intercalation selectivity of the anions in relation to the LDH. In the latter case the introduction of the positive charge into LDH structure was compensated for by the release from the solid of the equivalent quantity of lithium and hydrogen cations. Time-resolved in-situ X-ray diffraction measurements have revealed that the chelation/intercalation reactions proceed very quickly. The rate of the reaction found for nickel acetate depends on concentration as approximately k[Ni(Ac)(2)](3).     

Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds

In the standard electrospray ionization mass spectra of many common, low molecular mass organic compounds dissolved in methanol, peaks corresponding to ions with formula [3M + Met](2+) (M = organic molecule, Met = bivalent metal cation) are observed, sometimes with significant abundances. The most common are ions containing Mg(2+), Ca(2+) and Fe(2+). Their presence can be easily rationalized on the basis of typical organic reaction work-up procedures. The formation of [3M + Met](2+) ions has been studied using N-FMOC-proline methyl ester as a model organic ligand and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Fe(2+), Ni(2+), Mn(2+), Co(2+) and Zn(2+) chlorides or acetates as the sources of bivalent cation. It was found that all ions studied form [3M + Met](2+) complexes with N-FMOC-proline methyl ester, some of them at very low concentrations. Transition metal cations generally show higher complexation activity in comparison with alkaline earth metal cations. They are also more specific in the formation of [3M + Met](2+) complexes. In the case of alkaline earth metal cations [2M + Met](2+) and [4M + Met](2+) complex ions are also observed. It has been found that [3M + Met](2+) complex ions undergo specific fragmentation at relatively low energy, yielding fluorenylmethyl cation as a major product. [M + Na](+) ions are much more stable and their fragmentation is not as specific.     

Effect of energy dependence of primary beam divergence on the X-ray standing wave characterization of layered materials.

Incident primary beam divergence is a source of systematic error in X-ray standing wave (XSW) characterization of single and multilayer thin films. Primary beam divergence significantly alters the XSW profile of a layered material and can lead to large errors when used with higher excitation energies. The present study suggests that when one uses Mo-Kalpha excitation, the primary beam divergence should be in range of 0.005(0). On the other hand, in the case of Cu-Kalpha excitation, primary beam divergence can be relaxed up to 0.01(0).     

Interactions of metal ions with monoaza crown ethers A15C5 and A18C6 carrying dansyl fluorophore as pendant in acetonitrile solution

The influence of metal cations Li(+), Na(+), K(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+) and Al(3+) on the spectroscopic properties of the dansyl (1-dimethylaminonaphthalene-5-sulfonyl) group covalently linked to monoaza crown ethers 1-aza-15-crown-5 (1,4,7,10,-tetraoxa-13-azacyclopentadecane) (A15C5) and 1-aza-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) (A18C6) was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with both fluoroionophores is weak, while alkaline earth metal ions interact strongly causing 50 and 85% quenching of dansyl fluorescence of N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,-tetraoxa-13-azacyclopentadecane (A15C5-Dns) and N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (A18C6-Dns), respectively. The Cu(2+), Pb(2+) and Al(3+) cations interact very strongly with dansyl chromophore, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co(2+), Ni(2+), Zn(2+), Mg(2+) cations interact moderately with both fluoroionophores causing quenching of dansyl fluorescence by several percent only.     

Aldimines generated from aza-Wittig reaction between bis(iminophosphoranes) derived from 1,1'-diazidoferrocene and aromatic or heteroaromatic aldehydes: electrochemical and optical behaviour towards metal cations

Aldimine 4 bearing a 2-quinolyl group was prepared by aza-Wittig reaction between the triphenyliminophosphorane derived from the 1,1'-diazidoferrocene and 2-formylquinoline. However, aldimine 5, bearing a pyrene ring, was prepared using the most reactive tributyliminophosphorane derivative and the corresponding 1-formylpyrene. On the other hand, formation of aldimine 8 involves a tandem process, Staudinger reaction/intramolecular aza-Wittig reaction, by using directly 1,1'-diazidoferrocene and 2-(diphenylphosphonyl)benzaldehyde. Aldimine 4 behaves as chemosensor molecule for Ni(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+) cations through two different channels: electrochemical (ΔE(1/2) = 222-361 mV) and chromogenic (Δλ = 122-153 nm), which can be used for the "naked eye" detection of these metal cations. Aldimine 5 behaves as a highly selective redox (in CH(3)CN) and fluorescent (in CH(3)Cl-DMF) probe for Hg(2+) metal cations even in the presence of a large excess of the other metal cations tested. Aldimine 8 displays electrochemical affinity (ΔE(1/2) = 60-288 mV) to Li(+), Ca(2+), Mg(2+), Zn(2+) and Pb(2+) metal cations, with the phosphorus oxide functionality as a binding site. From the (1)H NMR titration data as well as DFT calculations, different tentative binding modes have been established, for these structurally related ferrocenyl derivatives.     

Test strips for lead(II) based on a unique color change of PVC-film containing O-donor macrocycles and an anionic dye.

Glassy test strips partially coated with PVC-film including O-donor macrocyclic receptors (L), tetrabromophenolphthalein ethyl ester (TBPE(-)), and a plasticizer sensed Pb(2+) in aqueous solutions by a unique color change. Yellow films successively changed color to green, dark-blue and purple with increases of the Pb(2+) concentration. In contrast with the ordinary "optode", a characteristic absorption band at 525 nm was newly appeared independently of the protonation and deprotonation of HTBPE (yellow to blue). The unique color change occurred only when asymmetric receptors with respect to the basal plane were coupled with Pb(2+). This optical-structural correlation is likely to be induced by the H aggregate of two sets of TBPE(-) in the 1:2 ion-pair, [Pb-L](2+).(TBPE(-))(2). The color change, based on metachromasy, was exclusive for Pb(2+) among common metal cations (Ca(2+), Al(3+), Cd(2+), Zn(2+), Fe(3+), Co(2+), Hg(2+)) and anions (Cl(-), SO(4)(2-), PO(4)(3-), S(2)O(3)(2-)).     

An iron(III) selective dendrite chelator based on polyamidoamine dendrimer modified with 4-bromo-1,8-naphthalimide

A new 4-bromo-1,8-naphthalimide-labelled polyamidoamine (PAMAM) dendrimer from zero generation has been synthesised and characterised. Its functional characteristics, determined in acetonitrile solvent are discussed. The ability of the dendrimer to detect metal cations has been evaluated in acetonitrile by monitoring the quenching of the fluorescence intensity. Different metal cations have been tested Co(2+), Ni(2+), Cu(2+) and Fe(3+) for the purpose. The results have shown clearly that only Fe(3+) could be efficiently detected using the dendrimer.     

Functionalized BODIPY with various sensory units - a versatile colorimetric and luminescent probe for pH and ions

A series of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives containing ion- and pH-sensory units have been successfully designed and synthesized. One of the compounds was structurally characterized by X-ray crystallography. Owing to the presence of an ICT absorption band, one of the compounds was found to show pronounced solvatochromic behavior in different organic solvents. Their emission energies in various solvents show a linear dependence on the Lippert solvent parameter. The cation-binding properties of the complexes with different metal ions (alkali metal, alkaline earth metal and transition metal ions) have been studied using UV-vis and emission spectroscopies. A 1?:?1 complexation to metal ions (Li(+), Na(+), Mg(2+), Ba(2+), Zn(2+), Cd(2+)) was found for the compound with one azacrown moiety in acetonitrile while another one with two azacrown moieties was shown to form 1?:?2 complexes with Zn(2+) and Mg(2+) cations. Their stability constants have been determined by both UV-vis and emission spectrophotometric methods. By introducing triarylborane moieties into the meso position and the 2-position of the BODIPY skeleton, different electronic absorption spectral changes together with an emission diminution were observed in response to fluoride ions. Ditopic binding study of 5, which was functionalized with both azacrown and triarylborane moieties, showed emission enhancement in the presence of Mg(2+) and F(-). These findings suggest that these BODIPY derivatives are capable of serving as versatile colorimetric and luminescence probes for pH, cations and F(-).     

Trace metal ion partitioning at polymer film-metal oxide interfaces: long-period X-ray standing wave study

The distributions of Pb(II) and As(V)O4(3-) ions in the interfacial region between thin poly(acrylic acid) (PAA) coatings and aalpha-A12O3(0001), alpha-Al2O3(1-102), and alpha-Fe2O3(0001) single-crystal substrates were studied using long-period X-ray standing wave fluorescent yield (XSW-FY) and X-ray reflectivity techniques. The PAA film serves as a simplified analogue of natural organic matter (NOM) coatings on mineral surfaces. Such coatings are often assumed to play an important role in the partitioning and speciation of trace heavy metals in soils and aquatic systems. On the alpha-Al2O3(1-102) surface, Pb(II) ions were found to preferentially bind to the PAA coating, even at sub-micromolar Pb(II) concentrations, and to partition increasingly onto the metal oxide surface as the Pb(II) concentration was increased ([Pb(II)] = 5 x 10(-8) to 2 x 10(-5) M, pH = 4.5; 0.01 M NaCl background electrolyte). This observation suggests that the binding sites in the PAA coating outcompete those on the alpha-Al2O3(1-102) surface for Pb(II) under these conditions. The As(V)O4(3-) oxoanion partitions preferentially to the L-Al2O3(1-102) surface for the As(V)O4(3-) concentrations examined (1 x 10(-7) to 5 x 10(-7) M, pH = 4.5; 0.01 M NaCl background electrolyte). Partitioning of Pb(II) (at 1 x 10(-7) M and pH 4.5) was also examined at PAA/alpha-Al2O3(0001), and PAA/alpha-Fe2O3(0001) interfaces using XSW-FY measurements. Our results show that the PAA coating was the dominant sink for Pb(II) in all three samples; however, the relative order of reactivity of these metal oxide surfaces with respect to Pb(II) sorption is alpha-Fe2O3(0001) > alpha-Al2O3(1-102) > alpha-Al2O3(0001). This order is consistent with that found in previous studies of the PAA-free surfaces. These XSW results strongly suggest that the characteristics of the organic film (i.e., binding affinity, type, and density of binding sites) as well as metal oxide substrate reactivity are key factors determining the distribution and speciation of Pb(II) and As(V)O4(3-) at organic film/metal oxide interfaces.     

Novel heterometal-organic complexes as first single source precursors for up-converting NaY(Ln)F4 (Ln = Yb, Er, Tm) nanomaterials

First heterometal-organic single source precursors for NaYF(4) nanomaterials as a host matrix for up-conversion emission are reported. These novel heterobimetallic derivatives NaY(TFA)(4)(diglyme) (1), [Na(triglyme)(2)][Y(2)(TFA)(7)(THF)(2)] (2) and Na(2)Y(TFA)(5)(tetraglyme) (3) (TFA = trifluoroacetate), which were fully characterized by elemental analysis, FT-IR and (1)H NMR spectroscopy, TG-DTA data as well as single crystal X-ray structures, are advantageous in terms of being anhydrous and having lower decomposition temperatures in comparison to the homometallic precursor Y(TFA)(3)(H(2)O)(3). In addition, they also contain chelating glyme ligands, which act as capping reagents during decomposition to control the NaYF(4) particle size and render them monodisperse in organic solvents. On decomposition in 1-octadecene, the molecular derivatives 1 and 3 are converted, in the absence of any surfactant or capping reagent, to cubic NaYF(4) nanocrystals at significantly lower temperatures (below 250 °C). At higher temperature, a mixture of the cubic and hexagonal phases was obtained, the relative ratio of the two phases depending on the reaction temperature. A pure hexagonal phase, which is many folds more efficient for UC emission than the cubic phase, was obtained by calcining nanocrystals of mixed phase at 400 °C. In order to co-dope this host matrix with up-converting lanthanide cations, analogous complexes NaLn(TFA)(4)(diglyme) [Ln = Er (4), Tm (5), Yb (6)] and Na(2)Ln(TFA)(5)(tetraglyme) [Ln = Er (7), Yb (8)] were also prepared and characterized. The decomposition in 1-octadecene of suitable combinations and appropriate molar ratios of these yttrium, ytterbium and erbium/thulium derivatives gave cubic and/or hexagonal NaYF(4): Yb(3+), Er(3+)/Tm(3+) nanocrystals (NCs) capped by diglyme or tetraglyme ligands, which were characterized by IR, TG-DTA data, EDX analysis and TEM studies. Surface modification of these NCs by ligand exchange reactions with poly acrylic acid (PAA) and polyethyleneglycol (PEG) diacid 600 was also carried out to render them water soluble. The THF solutions of suitable combinations of the diglyme derivatives were also used to elaborate the thin films of NaYF(4):Yb(3+), Er(3+)/Tm(3+) on a glass or Si wafer substrate by spin coating. The multicolour up-conversion fluorescence was successfully realized in the Yb(3+)/Er(3+) (green/red) and Yb(3+)/Tm(3+) (blue/violet) co-doped NaYF(4) nanoparticles and thin films, which demonstrates that they are promising UC nanophosphors of immense practical interest. The up-conversion excitation pathways for the Er(3+)/Yb(3+) and Tm(3+)/Yb(3+) co-doped materials are discussed.     

Highly sensitive and fast responsive fluorescence turn-on chemodosimeter for Cu2+ and its application in live cell imaging

A rhodamine B derivative 4 containing a highly electron-rich S atom has been synthesized as a fluorescence turn-on chemodosimeter for Cu(2+). Following Cu(2+)-promoted ring-opening, redox and hydrolysis reactions, comparable amplifications of absorption and fluorescence signals were observed upon addition of Cu(2+); this suggests that chemodosimeter 4 effectively avoided the fluorescence quenching caused by the paramagnetic nature of Cu(2+). Importantly, 4 can selectively recognize Cu(2+) in aqueous media in the presence of other trace metal ions in organisms (such as Fe(3+), Fe(2+), Cu(+), Zn(2+), Cr(3+), Mn(2+), Co(2+), and Ni(2+)), abundant cellular cations (such as Na(+), K(+), Mg(2+), and Ca(2+)), and the prevalent toxic metal ions in the environment (such as Pb(2+) and Cd(2+)) with high sensitivity (detection limit < or =10 ppb) and a rapid response time (< or =1 min). Moreover, by virtue of the chemodosimeter as fluorescent probe for Cu(2+), confocal and two-photon microscopy experiments revealed a significant increase of intracellular Cu(2+) concentration and the subcellular distribution of Cu(2+), which was internalized into the living HeLa cells upon incubation in growth medium supplemented with 50 muM CuCl(2) for 20 h.     

Synthesis and Properties of 5-Chloro-8-hydroxyquinoline-Substituted Azacrown Ethers: A New Family of Highly Metal Ion-Selective Lariat Ethers

New 5-chloro-8-hydroxyquinoline (CHQ)-substituted aza-18-crown-6 (4), diaza-18-crown-6 (1), diaza-21-crown-7 (2), and diaza-24-crown-8 (3) ligands, where CHQ was attached through the 7-position, and aza-18-crown-6 (11) and diaza-18-crown-6 (10) macrocycles, where CHQ was attached through the 2-position, were prepared. Thermodynamic quantities for complexation of these CHQ-substituted macrocycles with alkali, alkaline earth, and transition metal ions were determined in absolute methanol at 25.0 degrees C by calorimetric titration. Two isomers, 1 and 10, which are different only in the attachment positions of the CHQ to the parent macroring, exhibit remarkable differences in their affinities toward the metal ions. Compound 1 forms very stable complexes with Mg(2+), Ca(2+), Cu(2+), and Ni(2+) (log K = 6.82, 5.31, 10.1, and 11.4, respectively), but not with the alkali metal ions. Ligand 10 displays strong complexation with K(+) and Ba(2+) (log K = 6.61 and 12.2, respectively) but not with Mg(2+) or Cu(2+). The new macrocycles and their complexes have been characterized by means of UV-visible and (1)H NMR spectra and X-ray crystallography. New peaks in the UV spectrum of the Mg(2+)-1 complex could allow an analytical determination of Mg(2+) in very dilute solutions in the presence of other alkali and alkaline earth metal cations. (1)H NMR spectral and X-ray crystallographic studies indicate that ligand 10 forms a cryptate-like structure when coordinated with K(+) and Ba(2+), which induces an efficient overlap of the two hydroxyquinoline rings. Such overlapping forms a pseudo second macroring that results in a significant increase in both complex stability and cation selectivity.     

Layer-by-layer self-assembled ultrathin multilayer films of lanthanide polyoxometalates and poly(allylamine hydrochloride) and their photoluminescent properties

Ultrathin multilayer films of two lanthanide polyoxometalates (LPOMs), K(17)[Eu(P(2)W(17)O(61))(2)] (EPW) and K(13)[Eu(SiW(11)O(39))(2)] (ESW), and poly(allylamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. UV-vis spectroscopy and ellipsometry respectively show that the absorbance values at characteristic wavelengths and the thicknesses of the multilayer films increase linearly with the number of LPOM/PAH bilayers, suggesting that the deposition process is linear and highly reproducible from layer to layer. Average thicknesses of ca. 3.4 and 2.4 nm were determined for the EPW/PAH and ESW/PAH bilayers by ellipsometry, respectively. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide the surface morphology of the LPOM/PAH films, indicating that the film surface is relatively uniform and smooth. The photoluminescent properties of these films have also been investigated by fluorescence spectroscopy. The LPOM/PAH multilayer film has a good thermal stability as shown by UV-vis, X-ray photoelectron, and fluorescence spectra.     

Adsorption-induced intramolecular dipole: correlating molecular conformation and interface electronic structure

The interfaces formed between pentacene (PEN) and perfluoropentacene (PFP) molecules and Cu(111) were studied using photoelectron spectroscopy, X-ray standing wave (XSW), and scanning tunneling microscopy measurements, in conjunction with theoretical modeling. The average carbon bonding distances for PEN and PFP differ strongly, that is, 2.34 A for PEN versus 2.98 A for PFP. An adsorption-induced nonplanar conformation of PFP is suggested by XSW (F atoms 0.1 A above the carbon plane), which causes an intramolecular dipole of approximately 0.5 D. These observations explain why the hole injection barriers at both molecule/metal interfaces are comparable (1.10 eV for PEN and 1.35 eV for PFP) whereas the molecular ionization energies differ significantly (5.00 eV for PEN and 5.85 eV for PFP). Our results show that the hypothesis of charge injection barrier tuning at organic/metal interfaces by adjusting the ionization energy of molecules is not always readily applicable.     

Serendipity and design in the generation of new coordination polymers: an extensive series of highly symmetrical guanidinium-templated, carbonate-based networks with the sodalite topology

The serendipitous discovery of a 3D [Cu(CO(3))(2)(2-)](n) network with the topology of the 4(2)6(4) sodalite net in [Cu(6)(CO(3))(12)(CH(6)N(3))(8)].K(4).8H(2)O paved the way for the deliberate engineering of an extensive series of structurally related guanidinium-templated metal carbonates of composition [M(6)(CO(3))(12)(CH(6)N(3))(8)]Na(3-)[N(CH(3))(4)].xH(2)O, where the divalent metal M in the framework may be Mg, Mn, Fe, Co, Ni, Cu, Zn, or Cd. A closely related crystalline material with a [Ca(CO(3))(2)(2-)](n) sodalite-like framework, but containing K(+) rather than Na(+), of composition [Ca(6)(CO(3))(12)(CH(6)N(3))(8)]K(3)[N(CH(3))(4)].3H(2)O was also isolated. All of these compounds were obtained under the simplest possible conditions from aqueous solution at room temperature, and their structures were determined by single-crystal X-ray diffraction. Pairs of guanidinium cations are associated with the hexagonal windows of the sodalite cages, alkali-metal cations are associated with their square windows, and N(CH(3))(4)(+) ions are located at their centers. Structures fall into two classes depending on the metal, M(II), in the framework. One type, the BC type (Im3m), comprising the compounds for which M(2+) = Ca(2+), Mn(2+), Cu(2+), and Cd(2+), has a body-centered cubic unit cell, while the second type, the FC type (Fd3c), for which M(2+) = Mg(2+), Fe(2+), Co(2+), Ni(2+), and Zn(2+), has a face-centered cubic unit cell with edges on the order of twice those of the BC structural type. The metal M in the BC structures has four close carbonate oxygen donors and four other more distant ones, while M in the FC structures has an octahedral environment consisting of two bidentate chelating carbonate ligands and two cis monodentate carbonate ligands.