Distribution by Scientific Domains
Distribution within Psychology

Kinds of Dyads

  • acceptor dyad
  • adolescent dyad
  • c60 dyad
  • child dyad
  • female dyad
  • fullerene dyad
  • infant dyad
  • mother-infant dyad
  • porphyrin dyad
  • subordinate dyad

  • Terms modified by Dyads

  • dyad type

  • Selected Abstracts

    Sexual devolution in plants: apomixis uncloaked?

    BIOESSAYS, Issue 9 2008
    Richard D. Noyes
    There are a growing number of examples where naturally occurring mutations disrupt an established physiological or developmental pathway to yield a new condition that is evolutionary favored. Asexual reproduction by seed in plants, or apomixis, occurs in a diversity of taxa and has evolved from sexual ancestors. One form of apomixis, diplospory, is a multi-step development process that is initiated when meiosis is altered to produce an unreduced rather than a reduced egg cell. Subsequent parthenogenetic development of the unreduced egg yields genetically maternal progeny. While it has long been apparent from cytological data that meiosis in apomicts was malfunctional or completely bypassed, the genetic basis of the phenomenon has been a long-standing mystery. New data from genetic analysis of Arabidopsis mutants1 in combination with more sophisticated molecular understanding of meiosis in plants indicate that a weak mutation of the gene SWI, called DYAD, interferes with sister chromatid cohesion in meiosis I, causes synapsis to fail in female meiosis and yields two unreduced cells. The new work shows that a low percentage of DYAD ovules produce functional unreduced egg cells (2n) that can be fertilized by haploid pollen (1n) to give rise to triploid (3n) progeny. While the DYAD mutants differ in some aspects from naturally occurring apomicts, the work establishes that mutation to a single gene can effectively initiate apomictic development and, furthermore, focuses efforts to isolate apomixis genes on a narrowed set of developmental events. Profitable manipulation of meiosis and recombination in agronomically important crops may be on the horizon. BioEssays 30:798,801, 2008. © 2008 Wiley Periodicals, Inc. [source]

    Redox Active Two-Component Films of Palladium and Covalently Linked Zinc Porphyrin,Fullerene Dyad

    ELECTROANALYSIS, Issue 9 2006
    Marta Plonska
    Abstract Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C60 covalently linked to zinc meso -tetraphenyloporphyrin, ZnPC60, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnPC60/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties. [source]

    Opening Up the Investor,Investee Dyad: Syndicates, Teams, and Networks

    Andy Lockett
    First page of article [source]

    Close Proximity Dibenzo[a,c]phenazine,Fullerene Dyad: Synthesis and Photoinduced Singlet Energy Transfer

    Rajeev K. Dubey
    Abstract A dibenzo[a,c]phenazine,fullerene (DBPZ-C60) dyad in which two chromophores are linked in close proximity to each other has been synthesized and studied in detail by optical spectroscopy to explore a new energy donor,acceptor system. The dyad was prepared by Prato reaction between 11-formyldibenzo[a,c]phenazine and fullerene. 3,5-Di- tert -butylbenzyl group was introduced onto the fulleropyrrolidine unit to achieve adequate solubility of the dyad. A thorough study of the photophysical properties of the dyad and relevant reference compounds, performed by means of steady state and time resolved spectroscopic measurements, has revealed the presence of highly efficient (ca. 98,%) and extremely fast (ken = 5,×,1011 s,1) intramolecular photoinduced singlet,singlet energy-transfer process from singlet excited state of the DBPZ moiety to fullerene. In both polar and nonpolar environment transduction of singlet excited state energy governs the excited state deactivation, but the efficiency and rate of energy transfer were found to be higher in nonpolar solvents in comparison to polar. The DBPZ singlet excited state decays within 2 and 4.7 ps in toluene andbenzonitrile, respectively, via singlet,singlet energy transfer to produce a fullerene singlet excited state which decays with a life time of 1.5 ns to give a very long-lived fullerene triplet state as final populated excited state. [source]

    Supramolecular Self-Assembly: Self-Assembly of a Donor-Acceptor Dyad Across Multiple Length Scales: Functional Architectures for Organic Electronics (Adv. Funct.

    More than the sum of its parts: by covalently coupling polycyclic donor and acceptor moieties, Samori and co-workers demonstrate on page 2486 that a donor,acceptor dyad, based on nanographene and perylene, self-assembles into highly ordered supramolecular architectures with nanosegregated coaxial donor and acceptor regions. The cover image features an atomic force microscopy image of mesoscopic ribbons along with the proposed crystallographic arrangement of the constituent molecules. [source]

    Self-Assembly of a Donor-Acceptor Dyad Across Multiple Length Scales: Functional Architectures for Organic Electronics

    Jeffrey M. Mativetsky
    Abstract Molecular dyads based on polycyclic electron donor (D) and electron acceptor (A) units represent suitable building blocks for forming highly ordered, solution-processable, nanosegregated D-A domains for potential use in (opto)electronic applications. A new dyad, based on alkyl substituted hexa- peri -hexabenzocoronene (HBC) and perylene monoimide (PMI) separated by an ethinylene linker, is shown to have a high tendency to self-assemble into ordered supramolecular arrangements at multiple length scales: macroscopic extruded filaments display long-range crystalline order, nanofiber networks are produced by simple spin-coating, and monolayers with a lamellar packing are formed by physisorption at the solution-HOPG interface. Moreover, highly uniform mesoscopic ribbons bearing atomically flat facets and steps with single-molecule heights self-assemble upon solvent-vapor annealing. Electrical measurements of HBC-PMI films and mesoscopic ribbons in a transistor configuration exhibit ambipolar transport with well balanced p- and n-type mobilities. Owing to the increased level of order at the supramolecular level, devices based on ribbons show mobility increases of more than one order of magnitude. [source]

    Unraveling the Dyad: Using Recurrence Analysis to Explore Patterns of Syntactic Coordination Between Children and Caregivers in Conversation

    LANGUAGE LEARNING, Issue 3 2006
    Rick Dale
    Recurrence analysis is introduced as a means to investigate syntactic coordination between child and caregiver. Three CHILDES (MacWhinney, 2000) corpora are analyzed and demonstrate coordination between children and their caregivers in terms of word-class n -gram sequences. Results further indicate that trade-offs in leading or following this coordination reflect individual differences between children at varying levels of development. Further analyses characterize the syntactic patterns that are coordinated, and results are consistent with recent language acquisition research on syntax acquisition. Overall, recurrence analysis reveals that there is a process of child-caregiver coordination taking place in ongoing conversation at the level of syntactic description. [source]

    Homogeneous Photocatalytic Oxidation of Alcohols by a Chromophore,Catalyst Dyad of Ruthenium Complexes,

    ANGEWANDTE CHEMIE, Issue 51 2009
    Weizhong Chen Dr.
    Eine Chromophor-Katalysator-Dyade aus Rutheniumpolypyridylkomplexen wurde synthetisiert und sowohl strukturell als auch elektronisch charakterisiert. Ihre Eignung für die protonengekoppelte Mehrelektronenphotooxidation wurde anhand der photokatalytischen Oxidation aliphatischer und benzylischer Alkohole unter Bestrahlung mit sichtbarem Licht gezeigt, die in Wasser unter Umgebungsbedingungen hohe Selektivitäten und Umsatzzyklen über 100 liefert. [source]

    Synthesis and Spectroscopic Properties of a Covalently Linked Porphyrin,Fullerene C60 Dyad.

    CHEMINFORM, Issue 41 2006
    M. Elisa Milanesio
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    Organoplatinum(II) Complexes with Chromophore,Acceptor Dyad Studied by Ultrafast Time-Resolved Absorption Spectroscopy

    Siu-Wai Lai Dr.
    Femtosecond time-resolved absorption revealed the formation of charged-separated [ClPtIII{C,N,N(PhMV+,)}] species (left) with a forward rate constant of about 1012,s,1, which is more rapid than that of the back electron-transfer process (k,1=1.6×109,s,1). Similar slower back ET reaction than forward light-induced ET reaction of [Pt(MV-bpy)(CCPh)2](PF6)2 (right) has been observed. MV=methyl viologen. [source]

    Off the Back or on the Side: Comparison of meso and 2-Substituted Donor-Acceptor Difluoroborondipyrromethene (Bodipy) Dyads

    Andrew C. Benniston
    Abstract The preparation of several difluoroborondipyrromethene (Bodipy) dyads is described incorporating covalently attached hydroquinone/quinone groups at the 2-position (BD-SHQ, BD-SQ, BD-SPHQ, BD-SPQ). The compounds, currently under investigation as chemical sensors for reactive oxygen species, show various levels of fluorescence depending on the oxidation state of the appended group. The 19F NMR spectrum for BD-SHQ in CDCl3 at room temperature reveals the two fluorines are inequivalent on the NMR timescale. In contrast, the 19F NMR spectrum for the counterpart quinone compound, BD-SQ, is consistent with two equivalent fluorine atoms. The two results are interpreted as the quinone is free to rotate around the connector bond, whereas this motion is restricted for the hydroquinone group and makes the fluorines chemically inequivalent. Cyclic voltammograms recorded for all derivatives in CH2Cl2 electrolyte solution are consistent with typical Bodipy-based redox chemistry; the potentials of which depend on factors such as presence of the phenylene spacer and oxidation state of the appended group. A comparison of the electrochemical behaviour with the counterpart meso derivatives reveals some interesting trends which are associated with the location of the HOMO/LUMOs. The absorption profiles for the compounds in CH3CN are again consistent with Bodipy-based derivatives, though there are some subtle differences in the band-shapes of the closely-coupled systems. In particular, the absorption spectra for the dyad, BD-SQ, in a wide range of solvents are appreciably broader than for BD-SHQ. Femtosecond transient absorption spectroscopy performed on the hydroquinone derivatives, BD-SHQ and its meso analogue is interpreted as electron transfer occurs from the hydroquinone unit to the first-excited singlet (S1) state of the Bodipy center, followed by ultrafast charge recombination to reinstate the ground state. The coupling of OH vibrations to the return electron transfer process is invoked to explain the lack of clear identification of the charge-separated state in the transient records. [source]

    Synthesis of Triazole-Bridged Unsymmetrical Porphyrin Dyads and Porphyrin,Ferrocene Conjugates

    Vijayendra S. Shetti
    Abstract A simple method has been used to synthesize four porphyrin azides with cores such as N4, N3S, N2SO and N2S2 in 60,90,% yields by treating the corresponding aminoporphyrins with tert -butyl nitrite (tBuONO) and azidotrimethylsilane (TMSN3) in THF/CH3CN under mild reaction conditions. The hitherto unknown aminoporphyrins with heteroatom cores were synthesized from their corresponding nitroporphyrins by standard SnCl2/HCl reduction. The azidoporphyrins were used to synthesize six triazole-bridged unsymmetrical porphyrin dyads containing two different types of porphyrin sub-units as well as five triazole-bridged porphyrin,ferrocene conjugates under CuI -catalyzed "click" reaction conditions. Various CuI -catalyzed reaction conditions were studied and the best yields of triazole-bridged dyads and conjugates were obtained with CuI/DIPEA in THF/CH3CN at room temperature for overnight. The unsymmetrical porphyrin dyads and porphyrin,ferrocene conjugates were characterized by various spectroscopic and electrochemical techniques. In unsymmetrical porphyrin dyads, the NMR, absorption and electrochemical studies indicate a weak interaction between the two porphyrin sub-units. However, preliminary photophysical studies support an efficient singlet-singlet energy transfer from one porphyrin unit to another in five unsymmetrical dyads reported here. In porphyrin,ferrocene conjugates, the fluorescence of porphyrin was quenched significantly due to photo-induced electron transfer from ferrocene to porphyrin. [source]

    Effects of self-enhancement on agreement on personality profiles

    Peter Borkenau
    Abstract Effects of self-enhancement and socially desirable responding (SDR) on rater agreement for personality profiles were studied in 304 students. Dyads of participants described themselves and their peer on the Revised NEO Personality Inventory (NEO-PI-R) that measures 30 facets of personality. In addition, participants filled in six scales measuring self-enhancement or SDR. Data analyses focussed on moderator and suppressor effects of SDR on the similarity between self-reported and other reported NEO-PI-R profiles. Three kinds of profile agreement were distinguished: (a) normative agreement; (b) distinctive agreement and (c) profile normativeness, that is, how strongly a self-reported personality profile resembled the average profile of all participants. There were no moderator or suppressor effects on distinctive agreement, but SDR predicted profile normativeness quite strongly. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    The Impact of Same-Sex LMX Dyads on Performance Evaluations

    Arup Varma
    Numerous studies have found that supervisors rate women lower than men for similar levels of performance, suggesting that for female employees, performance alone may not be able to guarantee fair ratings. What is not clear is whether this disparity is a function of the gender composition of the supervisor,subordinate dyad or simply a case of male supervisor rating behavior. Based on data from supervisor,subordinate dyads in four organizations, we found that after controlling for performance, both male and female supervisors exhibit a positive bias toward subordinates of the same sex and rate members of the same gender higher. © 2001 John Wiley & Sons, Inc. [source]

    Short-Term Reliability and Continuity of Emotional Availability in Mother,Child Dyads Across Contexts of Observation

    INFANCY, Issue 1 2006
    Marc H. Bornstein
    Emotional availability (EA) is a prominent index of socioemotional adaptation in the parent,child dyad. Is EA affected by context? In this methodological study, 34 mothers and their 2-year-olds were observed in 2 different settings (home vs. laboratory) 1 week apart. Significant cross-context reliability and continuity in EA as measured with the Emotional Availability Scales emerged. Because EA is not affected by context, cross-context generalizations about EA status in the dyad may be warranted. This work further documents the adequate psychometric properties of emotional availability. [source]

    Rhythm in Mother-Infant Interactions

    INFANCY, Issue 2 2003
    Deborah F. Deckner
    Rhythmic behavior and the association of vocal rhythmic behavior with language development were studied in a sample of 30 mother-infant dyads. Dyads were observed in 2 contexts (1 involved sharing pictures and the other sharing musical toys) when infants were 18 and 24 months of age. Vocal rhythmic behavior was seen in both contexts, and in both contexts mothers matched their infant's vocal rhythmic behavior at greater than chance rates. Greater matching tended to be associated with higher language scores whereas, counter to prediction, higher rates of maternal vocal rhythmic behavior tended to be associated with lower language scores. At 24 months of age, mother-daughter dyads showed more matching than mother-son dyads. These results suggest that differences in maternal production of vocal rhythmic behavior may foster different language learning strategies. [source]

    Interactional Input and The Incorporation of Feedback: An Exploration of NS,NNS and NNS,NNS Adult and Child Dyads

    LANGUAGE LEARNING, Issue 1 2003
    Alison Mackey
    Given the documented benefits of participation in communicative interaction (e.g., Gass & varonis, 1994; Mackey, 1999), the present study investigated the effects of interlocutor type on the provision and incorporation of feedback in task,based interaction. The interactions of 48 dyads, evenly divided among adults and children, and native speaker,nonnative speaker and nonnative speaker,native speaker, were analyzed to assess the effect of interlocutor on (1) amount of feedback, (2) opportunities for modified output, and (3) immediate incorporation of feedback. In all dyed types, at least 30% of errors resulted in feedback, much of which led to modified output. Analyses also revealed significant differences for amount, nature, and response to feedback according to dyad type. [source]

    Chlorin,Bacteriochlorin Energy-transfer Dyads as Prototypes for Near-infrared Molecular Imaging Probes: Controlling Charge-transfer and Fluorescence Properties in Polar Media

    Hooi Ling Kee
    The photophysical properties of two energy-transfer dyads that are potential candidates for near-infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads (FbC-FbB and ZnC-FbB) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2-dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ,(5,10 ps),1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (,f = 0.19) and singlet excited-state lifetimes (,,5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited-state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC-FbB than for ZnC-FbB in a given solvent. For example, the ,f and , values for FbC-FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC-FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge-transfer states, as assessed by ground-state redox potentials and supported by molecular-orbital energies derived from density functional theory calculations. Controlling the extent of excited-state quenching in polar media will allow the favorable photophysical properties of the chlorin,bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC-FbB, 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (,f = 760 nm), long bacteriochlorin excited-state lifetime (,5.5 ns), and narrow (,20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity- and lifetime-imaging techniques. [source]

    An experimental study of credibility in e-negotiations

    PSYCHOLOGY & MARKETING, Issue 2 2005
    Maryalice Citera
    E-negotiators' credibility was compared to that of face-to-face (FTF) negotiators in an integrative bargaining task. Dyads were randomly assigned to negotiate either on the computer or FTF. E-negotiators perceived their opponents to be less credible and reported less selfcredibility than FTF negotiators. Although lying did not vary significantly from FTF to e-negotiations, self-credibility and lying were negatively correlated. E-negotiators were also more likely to advocate using dishonesty in the future. Consistent with psychological distance theory, skepticism regarding the credibility of e-negotiators appears warranted. © 2005 Wiley Periodicals, Inc. [source]

    Through-Bond Energy Transfer Cassettes with Minimal Spectral Overlap between the Donor Emission and Acceptor Absorption: Coumarin,Rhodamine Dyads with Large Pseudo-Stokes Shifts and Emission Shifts,

    ANGEWANDTE CHEMIE, Issue 2 2010
    Weiying Lin Prof.
    Eine neue Klasse von Cumarin-Rhodamin-Systemen, die auf dem Energietransfer über Bindungen (TBET) beruhen und minimale Überlappung zwischen Donoremission und Akzeptorabsorption aufweisen, zeichnet sich durch große Pseudo-Stokes-Verschiebungen (bis 230,nm) und Emissionsverschiebungen (bis 170,nm) aus. Die Nützlichkeit dieser TBET-Plattform für die Entwicklung von TBET-Sonden wurde mit einer neuen ratiometrischen pH-Fluoreszenzsonde demonstriert. [source]

    Memory conformity: can eyewitnesses influence each other's memories for an event?

    Fiona Gabbert
    The current study investigated memory conformity effects between individuals who witness and then discuss a criminal event, employing a novel procedure whereby each member of a dyad watches a different video of the same event. Each video contained unique items that were thus seen only by one witness. Dyads in one condition were encouraged to discuss the event before each witness (individually) performed a recall test, while in a control condition dyads were not allowed to discuss the event prior to recall. A significant proportion (71%) of witnesses who had discussed the event went on to mistakenly recall items acquired during the discussion. There were no age-related differences in susceptibility to these memory conformity effects in younger (18,30 years) as compared to older (60,80 years) participants. Possible social and cognitive mechanisms underlying the distortions of memory due to conformity are discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Efficacy Beliefs in Coach,Athlete Dyads: Prospective Relationships Using Actor,Partner Interdependence Models

    APPLIED PSYCHOLOGY, Issue 2 2010
    Ben Jackson
    The overall purpose of the study was to investigate prospective actor and partner effects (cf. Kenny, Kashy, & Cook, 2006) of interpersonal efficacy beliefs in relation to relationship commitment, satisfaction, and effort within coach,athlete dyads. Fifty youth tennis players (mean age = 15.52 years, SD = 1.45) and their coaches (mean age = 40.17 years, SD = 13.71) provided data related to their self-efficacy, other-efficacy, and relation-inferred self-efficacy (RISE) beliefs mid-way through the competitive season. Three months later, participants provided data regarding personal effort, as well as relationship commitment and satisfaction. Actor,partner interdependence model analyses revealed positive actor effects for self-efficacy in relation to effort, and for other-efficacy in relation to commitment, effort, and satisfaction. Partner effects for other-efficacy were found in relation to relationship commitment and effort. Finally, actor and partner effects were also evident for RISE beliefs; however, these relationships were moderated by the individual's role (i.e. athlete or coach), such that the direction of actor and partner effects differed for athletes and coaches. Implications for fostering effective coach,athlete relationships are discussed. Cette recherche avait pour objectif général l'étude des retombées éventuelles sur l'acteur et son partenaire (Cf.: Kenny, Kashy & Cook, 2006) des croyances en l'efficience interpersonnelle en relation avec l'implication, la satisfaction et l'effort au sein de la dyade entraîneur-athlète. Cinquante jeunes joueurs de tennis (âge moyen = 15,52; ,= 1,45) et leurs entraîneurs (âge moyen = 40,17; ,= 13,71) ont fourni des données relatives à leurs représentations concernant l'auto-efficience, l'efficience d'autrui et l'auto-efficience émanant de la relation (RISE), cela au milieu de la période des compétitions. Trois mois plus tard, les sujets ont donné des informations se rapportant à leur effort personnel, leur implication relationnelle et leur satisfaction. Les analyses relevant du modèle de l'interdépendance acteur-partenaire ont révélé des conséquences positives pour l'acteur en ce qui concerne l'auto-efficience en relation avec l'effort et l'efficience d'autrui en relation avec l'implication, l'effort et la satisfaction. Les effets du partenaire pour l'efficacité d'autrui étaient en relation avec l'effort et l'implication relationnelle. Finalement, les effets du partenaire et de l'acteur apparaissaient également pour les croyances RISE; ces relations étaient toutefois modulées par les rôles individuels (athlète ou entraîneur), de telle sorte que le sens des effets acteur-partenaire différait pour les athlètes et les entraîneurs. On réfléchit aux applications permettant d'améliorer l'efficacité des relations athlète-entraîneur. [source]

    First Syntheses and Electronic Properties of (Oligo)phenothiazine,C60 Dyads.

    CHEMINFORM, Issue 2 2007
    Nadine Bucci
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    Synthesis and Electronic Properties of (Oligo)phenothiazine-ethynyl-hydro-C60 Dyads.

    CHEMINFORM, Issue 2 2007
    Nadine Bucci
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    ChemInform Abstract: Parallel (Face-to-Face) versus Perpendicular (Edge-to-Face) Alignment of Electron Donors and Acceptors in Fullerene Porphyrin Dyads: The Importance of Orientation in Electron Transfer.

    CHEMINFORM, Issue 3 2002
    Dirk M. Guldi
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Probing the Donor,Acceptor Proximity on the Physicochemical Properties of Porphyrin,Fullerene Dyads: "Tail-On" and "Tail-Off" Binding Approach.

    CHEMINFORM, Issue 38 2001
    Francis D'Souza
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Pentacene-Based Polycyclic Aromatic Hydrocarbon Dyads with Cofacial Solid-State ,-Stacking

    Dan Lehnherr
    Give me five! Pentacene-based polycyclic aromatic hydrocarbon (PAH) dyads are synthesized via an unsymmetrical pentacene building block. These molecules exhibit cofacial solid-state ,-stacking as a result of the large aromatic chromophores. The choice of the PAH attached to the pentacene (see picture) influences the electronic properties as determined by UV/Vis absorption/emission spectroscopy and cyclic voltammetry. [source]

    Light-Driven Charge Separation in Isoxazolidine,Perylene Bisimide Dyads

    Heinz Langhals Prof.
    Abstract A series of arrays for light-driven charge separation is presented, in which perylene tetracarboxylic bisimide is the light-absorbing chromophore and electron acceptor, whereas isoxazolidines are colourless electron donors, the electron-releasing properties of which are increased with respect to the amino group by means of the ,-effect. Charge separation (CS) in toluene over a distance ranging from ,10 to ,16,Å, with efficiencies of ,95 to ,50,% and CS lifetimes from 300,ps to 15,ns, are demonstrated. In dichloromethane the charge recombination reaction is faster than charge separation, preventing accumulation of the CS state. The effects of solvent polarity and molecular structure are discussed in the frame of current theories. [source]

    Single-Step Electron Transfer on the Nanometer Scale: Ultra-Fast Charge Shift in Strongly Coupled Zinc Porphyrin,Gold Porphyrin Dyads

    Jérôme Fortage Dr.
    Abstract The synthesis, electrochemical properties, and photoinduced electron transfer processes of a series of three novel zinc(II),gold(III) bisporphyrin dyads (ZnPSAuP+) are described. The systems studied consist of two trisaryl porphyrins connected directly in the meso position via an alkyne unit to tert -(phenylenethynylene) or penta(phenylenethynylene) spacers. In these dyads, the estimated center to center interporphyrin separation distance varies from 32 to 45,Å. The absorption, emission, and electrochemical data indicate that there are strong electronic interactions between the linked elements, thanks to the direct attachment of the spacer on the porphyrin ring through the alkyne unit. At room temperature in toluene, light excitation of the zinc porphyrin results in almost quantitative formation of the charge shifted state .+ZnPSAuP., whose lifetime is in the order of hundreds of picoseconds. In this solvent, the charge-separated state decays to the ground state through the intermediate population of the zinc porphyrin triplet excited state. Excitation of the gold porphyrin leads instead to rapid energy transfer to the triplet ZnP. In dichloromethane the charge shift reactions are even faster, with time constants down to 2,ps, and may be induced also by excitation of the gold porphyrin. In this latter solvent, the longest charge-shifted lifetime (,=2.3,ns) was obtained with the penta-(phenylenethynylene) spacer. The charge shift reactions are discussed in terms of bridge-mediated super-exchange mechanisms as electron or hole transfer. These new bis-porphyrin arrays, with strong electronic coupling, represent interesting molecular systems in which extremely fast and efficient long-range photoinduced charge shift occurs over a long distance. The rate constants are two to three orders of magnitude larger than for corresponding ZnPAuP+ dyads linked via meso -phenyl groups to oligo-phenyleneethynylene spacers. This study demonstrates the critical impact of the attachment position of the spacer on the porphyrin on the electron transfer rate, and this strategy can represent a useful approach to develop molecular photonic devices for long-range charge separations. [source]

    Photoinduced Electron Transfer in ,-Cyclodextrin-Based Supramolecular Dyads: A Free-Energy-Dependence Study

    Bijitha Balan
    Abstract Photoinduced electron transfer (PET) between ,-cyclodextrin-appended pyrene (PYCD) and a few acceptor molecules was studied in aqueous solutions. The pyrene moiety in PYCD is located above the narrower rim of the ,-CD and is fully exposed to water. The acceptors are monocyclic organic molecules and, upon dissolution in water in the presence of PYCD, a fraction of the donor,acceptor systems is present as supramolecular dyads and the remaining fraction as free molecules. Free-energy-dependence studies showed that electron transfer in the supramolecular dyads follows the Marcus equation. The donor,acceptor coupling and the reorganization energy were determined from fits of the data to the Marcus equation. The electronic coupling was found to be similar to those reported for hydrogen-bonded systems. It appears that the actual ,out values are somewhat lower than values calculated with the continuum model. The experimental design has also allowed, for the first time, a visual demonstration of the inverted region on the basis of the raw fluorescence lifetime data. [source]