Search

We report the synthesis of a series of n-extended dithienophospholes with phenyl or biphenyl terminal groups via Suzuki Miyaura cross-coupling procedures. The incorporation of the dithienophosphole core into the scaffold on oligophenylenes was found to lead to pronounced luminescence properties in solution and the solid state, the latter of which also responded to different solid-state morphologies, i.e., powder versus crystal. More importantly, the investigated molecular architectures also allowed--for the first time--the observation of ambipolar redox behavior of such species, with the biphenyl-extended species in particular showing quasi-reversible reduction and oxidation processes; the observed experimental features were correlated with computational density functional theory studies. Key words: phosphorus heterocycles, conjugated materials, organic electronics, luminescence, electrochemistry, ambipolar redox properties, DFT calculations. Nous presentons la synthese d'une serie de dithienophospholes a conjugaison n etendue portant des groupes terminaux phenyle ou biphenyle que nous avons realisee par couplage croise de Suzuki Miyaura. Nous avons observe que l'incorporation du noyau dithienophosphole aux oligophenylenes du squelette donnait lieu a des proprietes de luminescence marquees, en solution et a l'etat solide. Par ailleurs, ces proprietes se trouvaient modulees selon differentes morphologies de l'etat solide, a savoir la poudre ou le cristal. Fait important, les architectures moleculaires auxquelles nous nous sommes interesses permettaient egalement--pour la premiere fois--d'observer le comportement oxydoreducteur ambipolaire de telles especes, surtout dans le cas de celles qui etaient etendues grace aux groupes biphenyle, pour lesquelles on observait des processus de reduction et d'oxydation quasi-reversibles. Ces caracteristiques observees en conditions experimentales ont ete corroborees par des etudes de modelisation employant la theorie de la fonctionnelle de la densite. [Traduit par la Redaction] Mots-cles : heterocycles phosphores, substances conjuguees, electro-organique, luminescence, electrochimie, proprietes d'oxydoreduction ambipolaires, calculs DFT., Introduction Organic π-conjugated materials can exhibit intriguing photophysical properties such as high fluorescence quantum yields, charge/energy transfer, and tunable absorption/emission as well as valuable redox behavior and self-organization properties. (1-3) [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.07.027 Byline: Imke de Pater (a), Michael H. Wong (a), Philip Marcus (b), Statia Luszcz-Cook (a), Mate Adamkovics (a), Al Conrad (c), Xylar Asay-Davis (d), Christopher Go (e) Keywords: Jupiter, Atmosphere; Hubble Space Telescope observations; Infrared observations; Adaptive optics Abstract: We present observations and theoretical calculations to derive the vertical structure of and secondary circulation in jovian vortices, a necessary piece of information to ultimately explain the red color in the annular ring inside Jupiter's Oval BA. The observations were taken with the near-infrared detector NIRC2 coupled to the adaptive optics system on the 10-m W.M. Keck telescope (UT 21 July 2006; UT 11 May 2008) and with the Hubble Space Telescope at visible wavelengths (UT 24 and 25 April 2006 using ACS; UT 9 and 10 May 2008 using WFPC2). The spatial resolution in the near-IR ([approximately equal to]0.1-0.15a[sup.3] at 1-5[mu]m) is comparable to that obtained at UV-visible wavelengths ([approximately equal to]0.05-0.1a[sup.3] at 250-890nm). At 5[mu]m we are sensitive to Jupiter's thermal emission, whereas at shorter wavelengths we view the planet in reflected sunlight. These datasets are complementary, as images at 0.25-1.8[mu]m provide information on the clouds/hazes in the troposphere-stratosphere, while the 5-[mu]m emission maps yield information on deeper layers in the atmosphere, in regions without clouds. At the latter wavelength numerous tiny ovals can be discerned at latitudes between [approximately equal to]45[degrees]S and 60[degrees]S, which show up as rings with diameters [less than or approximately equal to]1000km surrounding small ovals visible in HST data. Several white ovals at 41[degrees]S, as well as a new red oval that was discovered to the west of the GRS, also reveal 5-[mu]m bright rings around their peripheries, which coincide with dark/blue rings at visible wavelengths. Typical brightness temperatures in these 5-[mu]m bright rings are 225-250K, indicative of regions that are cloud-free down to at least the [approximately equal to]4bar level, and perhaps down to 5-7bar, i.e., well within the water cloud. Radiative transfer modeling of the 1-2[mu]m observations indicates that all ovals, i.e., including the Great Red Spot (GRS), Red Oval BA, and the white ovals at 41[degrees]S, are overall very similar in vertical structure. The main distinction between the ovals is caused by variations in the particle densities in the tropospheric-stratospheric hazes (2-650mbar). These are 5-8 times higher above the red ovals than above the white ones at 41[degrees]S. The combination of the 5-[mu]m rings and the vertical structure derived from near-IR data suggests anticyclones to extend vertically from (at least) the water cloud ([approximately equal to]5bar) up to the tropopause ([approximately equal to]100-200mbar), and in some cases into the stratosphere. Based upon our observations, we propose that air is rising along the center of a vortex, and descending around the outer periphery, producing the 5-[mu]m bright rings. Observationally, we constrain the maximum radius of these rings to be less than twice the local Rossby deformation radius, L.sub.R . If the radius of the visible oval (i.e., the clouds that make the oval visible) is >3000 km, our observations suggest that the descending part of the secondary circulation must be within these ovals. For the Red Oval BA, we postulate that the return flow is at the location of its red annulus, which has a radius of [approximately equal to]3000km. We develop a theory for the secondary circulation, where air is (baroclinically) rising along the center of a vortex in a subadiabatic atmosphere, and descending at a distance not exceeding [approximately equal to]2x the local Rossby deformation radius. Using this model, we find a timescale for mixing throughout the vortex of order several months, which suggests that the chromophores that are responsible for the red color of Oval BA's red annulus must be produced locally, at the location of the annulus. This production most likely results from the adiabatic heating in the descending part of the secondary circulation. Such higher-than-ambient temperature causes NH.sub.3-ice to sublime, which will expose the condensation nuclei, such as the red chromophores. Author Affiliation: (a) Astronomy Department, 601 Campbell Hall, University of California, Berkeley, CA 94720, United States (b) Department of Mechanical Engineering, Program of Applied Science & Technology, University of California, Berkeley, CA 94720, United States (c) W.M. Keck Observatory, Waimea, HI 96743, United States (d) Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM 87545, United States (e) Physics Department, University of San Carlos, Nasipit, Talamban, Cebu City, Philippines Article History: Received 22 October 2009; Revised 28 July 2010; Accepted 30 July 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.05.013 Byline: Lynda Erskine (a), Eloisa Herrera (b) Keywords: Retinal ganglion cell; Optic pathway; Visual system; Axon guidance; Growth cone Abstract: The developing visual system has proven to be one of the most informative models for studying axon guidance decisions. The pathway is composed of the axons of a single neuronal cell type, the retinal ganglion cell (RGC), that navigate through a series of intermediate targets on route to their final destination. The molecular basis of optic pathway development is beginning to be elucidated with cues such as netrins, Slits and ephrins playing a key role. Other factors best characterised for their role as morphogens in patterning developing tissues, such as sonic hedgehog (Shh) and Wnts, also act directly on RGC axons to influence guidance decisions. The transcriptional basis of the spatial-temporal expression of guidance cues and their cognate receptors within the developing optic pathway as well as mechanisms underlying the plasticity of guidance responses also are starting to be understood. This review will focus on our current understanding of the molecular mechanisms directing the early development of functional connections in the developing visual system and the insights these studies have provided into general mechanisms of axon guidance. Author Affiliation: (a) Division of Visual Science, Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK (b) Instituto de Neurosciencias de Alicante, CSIC-UMH, 03550 San Juan de Alicante, Spain Article History: Received 20 February 2007; Revised 2 May 2007; Accepted 10 May 2007

The static and dynamic first hyperpolarizabilities for a series of substituted metallabenzene-based nonlinear optical chromophores are determined by time-dependent density functional theory. The electronic excitation contributions to the first hyperpolarizability are rationalized in terms of the two-level model.

The properties of the covalently linked porphyrin arrays are different from those of the monomers. Use of 'active' linkers may result in ultrafast transfer of energy over long distances.

Electronic absorption spectroscopy and cyclic voltammetry techniques are employed to characterize six new dicationic two-dimensional nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors synthesized from nucleophilic substitutions of 2,6-dichloropyrazine with pyridyl derivatives.

The ultrafast resonant energy transfer of a perylene bisimide dyad is examined by using pump-probe spectroscopy, chemical variation and calculations. The temperature effects on the Forster resonant energy transfer rate has shown that energy transfer is enabled through low-frequency ground-state vibrations, which has broken the orthogonal arrangement of the transition dipole moments.

A facile method is developed to modify the surface of a fragile organic one-dimensional (1D) microstructure and white-light-emitting 1D microstructures are obtained by grafting red chromophores onto the surface of self-assembled blue-emissive microwires via a heterophase [S.sub.N]2 reaction. The ability to postfunctionalize organic 1D structure has enabled many applications, where the surface property has played key roles, such as an organic P-N junction and a biosensor.

A self-assembled DNA-based photonic wire is constructed that is capable of transporting excitation energy over a distance of more than 20 nm. The studies have shown that it is possible to create two component DNA-based photonic wires capable of long-range energy transfer by using a straightforward self-assembly approaches.

The syntheses of new blue luminescent [N.sup.2]-modified guanosine derivatives with chromophores p-4,4'-biphenyl-N[Ph.sub.2], p-4,4'-biphenyl-N[(2-py).sub.2], and p-4,4'-biphenyl-2-(2'-pyridyl)benzimidazolyl, are described. The anion-dependent circular dichroism (CD) response of the chromophores toward Zn(II) salt has shown the involvement of intramolecular hydrogen bonding between the acetate bound to the Zn(II) ion and the hydroxyl groups of the guanosine.

The design, synthesis and characterization of a new organic dye (P1) are described along with its performance in a photovoltaic device based on NiO as the photocathode and a passive anode (p-type dye-sensitized solar cells (DSSCs)). These systems are optimized by increasing the thickness of the semiconductor film and by optimizing the structure of the sensitizer.

A panel of antibodies elicited to the chromophoric antigen fluorescein is examined and the dynamics of the antibody-fluorescein complexes are compared by using three-pulse photon echo peak shift and transient grating spectroscopy. The studies have provided a gauge of the dynamic diversity of the antibody repertoire and have shown that the diversity has contributed to molecular recognition by facilitating the recognition of the broadcast range of foreign molecules.

The synthesis and live human cell internalization of europium hydroxide nanorods are described. Chromophore-to-[Eu.sup.3+] energy-transfer in the functionalized nanorods has enabled straining of the cytoplasm of living human cells, which is confirmed by costaining with fluorescent dextran.

A study was conducted to examine the two photon absorption (TPA) and photophysical properties of three new symmetrical chromophores with electron accepting phthalimide edge substituents. The experimental results for TPA photobleaching of solid poly(methylmethacrylate) films doped with the fluorene molecule revealed that the material could be used as an efficient TPA optical data storage medium.

Quantum chemical computations are used for evaluating the magnitudes of the perturbational, dipolar and direct covalent contributions to the electronic circular dichroism (CD) induced in porphyrin chromophores. The pure transition dipole coupling (TDC) has performed well for distant chromophores, but has displayed significant deviations from the quantum computations for shorter distances, such as those in parallel stacked porphyrins.

The quantum chemical calculations and resonance Raman spectroscopy are used for examining the chromophore delocalization in 4-hydroxy-4'-nitroazobenzene as well as in its deprotonated species. The results have shown considerable charge redistribution in the parent molecule after deprotonation, as shown by the red shift of the electronic transition and the change in the extension of the chromophore delocalization.

The implications of the dielectric effects on electronic energy transfer (EFT) couplings in photosynthetic antenna proteins are analyzed by using a quantum-mechanical model. The close packing between chromophores in natural antenna systems has led to reduced medium screening effects, enabling efficient energy migration and trapping.

The electronic absorption and third-order polarizability spectra of electron-donor acceptor molecular pairs of tetraalkylammonium halide/carbon tetrabromide complexes are investigated. The results show that the counterion indirectly affects the properties of these chromophores.

Two-dimensional infrared (2D-IR) spectroscopy is employed to study the dynamics of a multimode system, which is coupled to multiple heat baths. The methodology has proved to be very advantageous, as it provides detailed information on the electronic couplings among chromophores.

A study aimed at obtaining spectroscopic evidence of structural heterogeneity for LOV2 domain of Adiantum neochrome1. Results reveal that there are multiple local structures of flavin mononucleotide and cysteine in LOV2 domain of Adiantum neochrome1.

Infrared absorption experiments on light-triggered azobenzene peptides are performed below and above the freezing point of the solvent dimethyl sulfoxide (DMSO). The results have shown that at low temperatures the peptide, together with traces of water present in the sample, has formed a shell in the vicinity of the chromophore that facilitates internal motion even in the rigid cage of frozen DMSO.

The crystal structure of the cyan-fluorescent Cerulean green fluorescent protein (GFP), which is a variant of enhanced cyan fluorescent protein (ECFP), is determined. The results have shown that the high-resolution X-ray structure of Cerulean GFP is consistent with a single ground state conformation for the chromophore and its protein environment, although the broad absorbance doublet is persisting in the crystal.

The effect of temperature on the two-photon absorption cross section of azoaromatic chromophores is reported.

The characterization of Ppr from Rhodospirillum centenum and the interplay between the two chromophore domains are presented. The results have indicated that the function of the photoactive yellow protein (PYP) domain in Ppr is to act as a blue light switch to reverse the effects of red light on the Bph.

The study describes the three-dimensional energy transfer processes in a well-defined highly luminescent host-guest system, which exhibits high chromophore concentrations. The rapid energy migration along one direction of the strcuture accounts for an efficient energy transfer over very large distances at low acceptor concentrations.

The measurement of picosecond time-resolved ultraviolet resonance Raman (UVRR) spectra of photoactive yellow protein (PYP) reveal that spectral changes in bands of the tyrosine residue revealed that the hydrogen bond between Y42 and the chromophore becomes strong in the pG* state.

The time-dependent Stokes shifts of fluorescent dyes containing an anthroyloxy chromophore (2-AS, 9-AS, and 16-AP) in bilayers composed of palmitoyl-oleoyl-phosphatidylcholine is examined. The results have shown a nontrivial solvation response of these dyes, which are present in the backbone region of the bilayer with a gradually increasing depth.

The article introduces a new methodology, which can be easily used for the preferential end functionalization of the gold (Au) nanorods with Au nanoparticles by exploiting the electrostatic interactions. The described technique has proved to be extremely beneficial, as it can be used for connecting nanorods onto microelectrodes, alloying specific domains of nanorods and also for functionalizing chromophores on their edges.

The ultrafast femtosecond transient absorption spectroscopy is used to examine the excited-state dynamics of two-photon absorbing chromophores belonging to PRL series of dye molecules along with N[(DSB).sub.3] (tris[4-(3',5'-di-tert-butyldistyrylbenzenyl)phenyl]amine). The results have indicated an increase of charge-transfer character of the excited state with an increase in branching, thereby explaining the relative increase in the two-photon cross section of the PRL series.

A comprehensive experimental and theoretical investigation of a series platinum-acetylide oligomers of the general structure Ph-C=C-C-][Pt[L.sub.2]-C(triple bond)C- (1,4-Ph)-C(triple bond)C-].sub.n] - Pt[L.sub.2]C(triple bond)=C-Ph (where n=1,2,3,4,6; Ph=phenyl, 1,4-Ph=1,4-phenylene; L=P[(n-Bu).sub.3], and the geometry at Pt=trans) is carried out. The combined experimental and theoretical findings present very clear proof that the triplet excited state is localized on a chromophore consisting of a single -][Pt[L.sub.2]-C(triple bond)C-(1,4-Ph)-C(triple Bond)C-Pt[L.sub.2]]- repeat unit.