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Baytekin B.,Institute For Chemie Und Biochemie Der Freien University | Baytekin B.,Equilibrium Energy | Schalley C.,Institute For Chemie Und Biochemie Der Freien University
Chemistry - A European Journal | Year: 2012

Two rotaxanes with benzyl ether axles and tetralactam wheels were synthesized through an anion template effect. They carry naphthalene chromophores attached to the stopper groups and a pyrene chromophore attached to the wheel. The difference between the two rotaxanes is represented by the connecting unit of the naphthyl chromophore to the rotaxane axle: a triazole or an alkynyl group. Both rotaxanes exhibit excellent light-harvesting properties: excitation of the naphthalene chromophores is followed by energy transfer to the pyrene unit with efficiency higher than 90% in both cases. This represents an example of light-harvesting function among chromophores belonging to mechanically interlocked components, that is, the axle and the wheel of the rotaxanes. © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.


Li G.,Equilibrium Energy | Shishodia M.S.,Holon Institute of Technology | Shishodia M.S.,Tel Aviv University | Fainberg B.D.,Holon Institute of Technology | And 6 more authors.
Nano Letters | Year: 2012

We have studied the influence of both exciton effects and Coulomb repulsion on current in molecular nanojunctions. We show that dipolar energy-transfer interactions between the sites in the wire can at high voltage compensate Coulomb blocking for particular relationships between their values. Tuning this relationship may be achieved by using the effect of plasmonic nanostructure on dipolar energy-transfer interactions. © 2012 American Chemical Society.


Jannasch A.,TU Dresden | Demirors A.F.,University Utrecht | Demirors A.F.,Equilibrium Energy | Van Oostrum P.D.J.,University Utrecht | And 3 more authors.
Nature Photonics | Year: 2012

Optical tweezers are exquisite position and force transducers and are widely used for high-resolution measurements in fields as varied as physics, biology and materials science. Typically, small dielectric particles are trapped in a tightly focused laser and are often used as handles for sensitive force measurements. Improvement to the technique has largely focused on improving the instrument and shaping the light beam, and there has been little work exploring the benefit of customizing the trapped object. Here, we describe how anti-reflection coated, high-refractive-index core-shell particles composed of titania enable single-beam optical trapping with an optical force greater than a nanonewton. The increased force range broadens the scope of feasible optical trapping experiments and will pave the way towards more efficient light-powered miniature machines, tools and applications. © 2012 Macmillan Publishers Limited. All rights reserved.


Li G.,Equilibrium Energy | Nitzan A.,Tel Aviv University | Ratner M.A.,Equilibrium Energy | Ratner M.A.,Northwestern University
Physical Chemistry Chemical Physics | Year: 2012

A simple model is constructed to describe dissociation of charge transfer excitons in bulk heterojunction solar cells, and its dependence on the physical parameters of the system. In bulk heterojunction organic photovoltaics (OPVs), exciton dissociation occurs almost exclusively at the interface between the donor and acceptor, following one-electron initial excitation from the HOMO to the LUMO levels of the donor, and charge transfer to the acceptor to make a charge-transfer exciton. After exciton breakup, and neglecting the trapping of individual carriers, the electron may undergo two processes for decay: one process involves the electron and/or hole leaving the interface, and migrating to the electrode. This is treated here as the electron moving on a set of acceptor sites. The second loss process is radiationless decay following recombination of the acceptor electron with the donor cation; this is treated by adding a relaxation term. These two processes compete with one another. We model both the exciton breakup and the subsequent electron motion. Results depend on tunneling amplitude, energetics, disorder, Coulomb barriers, and energy level matchups, particularly the so-called LUMO-LUMO offset. © 2012 the Owner Societies.


Warren S.C.,Ecole Polytechnique Federale de Lausanne | Warren S.C.,Equilibrium Energy | Thimsen E.,Ecole Polytechnique Federale de Lausanne | Thimsen E.,Argonne National Laboratory
Energy and Environmental Science | Year: 2012

The study of the optoelectronic effects of plasmonic metal nanoparticles on semiconductors has led to compelling evidence for plasmon-enhanced water splitting. We review the relevant physics, device geometries, and research progress in this area. We focus on localized surface plasmons and their effects on semiconductors, particularly in terms of energy transfer, scattering, and hot electron transfer. © 2011 The Royal Society of Chemistry.


Dzyuba E.V.,Free University of Berlin | Baytekin B.,Free University of Berlin | Baytekin B.,Equilibrium Energy | Sattler D.,Free University of Berlin | Schalley C.A.,Free University of Berlin
European Journal of Organic Chemistry | Year: 2012

Bromo-substituted Hunter/Vögtle-type tetralactam macrocycles (TLMs) represent key intermediates for the attachment of terpyridyl and phenanthroline metal binding sites through cross-coupling reactions. From these monovalent precursors, metal complexes can easily be obtained that present the macrocycles in a multivalent fashion. Depending on the nature of the metal ion, the properties of the complexes can be tuned with respect to valency (e.g., phen-TLM + Cu I: divalent, phen-TLM + Fe II: trivalent) and lability against TLM ligand exchange (e.g., Cu I: slow, but reversible exchange, Ru IICl 2: kinetically inert). Hunter/Vögtle-type tetralactam macrocycles are equipped with metal coordination sites through Suzuki cross-coupling. The same bromo-substituted macrocycle can be used irrespective of the individual binding site, which provides versatile access to different complexes. The complexes represent multivalent hosts that are potentially useful for the formation of multiply interlocked molecules. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Timonen J.V.I.,Aalto University | Timonen J.V.I.,Equilibrium Energy | Latikka M.,Aalto University | Ikkala O.,Aalto University | Ras R.H.A.,Aalto University
Nature Communications | Year: 2013

The recently demonstrated extremely water-repellent surfaces with contact angles close to 180with nearly zero hysteresis approach the fundamental limit of non-wetting. The measurement of the small but non-zero energy dissipation of a droplet moving on such a surface is not feasible with the contemporary methods, although it would be needed for optimized technological applications related to dirt repellency, microfluidics and functional surfaces. Here we show that magnetically controlled freely decaying and resonant oscillations of water droplets doped with superparamagnetic nanoparticles allow quantification of the energy dissipation as a function of normal force. Two dissipative forces are identified at a precision of ∼ 10 nN, one related to contact angle hysteresis near the three-phase contact line and the other to viscous dissipation near the droplet-solid interface. The method is adaptable to common optical goniometers and facilitates systematic and quantitative investigations of dynamical superhydrophobicity, defects and inhomogeneities on extremely superhydrophobic surfaces. © 2013 Macmillan Publishers Limited. All rights reserved.


Wang D.,Northwestern Polytechnical University | Wang D.,Northwestern University | Tejerina B.,Equilibrium Energy | Lagzi I.,Northwestern University | And 3 more authors.
ACS Nano | Year: 2011

Selective aggregation and precipitation of like-charged nanoparticles (NPs) covered with carboxylate ligands can be induced by different monovalent cations. The ordering of critical concentrations required for NP precipitation is Cs+≫K+>Li+>Na+> Rb+ and does not correlate with the size of hydrated cations M +, nor can it be predicted by the Hofmeister series. On the other hand, different anions have no effect on the precipitation trends. These observations are rationalized by a theoretical model combining the elements of the DLVO theory with molecular-level calculations. The key component of the model is the cation-specific binding of various metal cations to the carboxylate ligands. © 2011 American Chemical Society.


Tejerina B.,Equilibrium Energy | Gothard C.M.,Northwestern University | Gothard C.M.,Equilibrium Energy | Grzybowski B.A.,Northwestern University | Grzybowski B.A.,Equilibrium Energy
Chemistry - A European Journal | Year: 2012

The interaction between tetrathiafulvalene and tetracation cyclobis(paraquat-p-phenylene) fragments-the key elements of many rotaxane systems-was investigated theoretically by using ab-initio second-order perturbation methods. In addition to the inclusion complex observed in the solid state, a thermodynamically stable "exterior" complex was identified. Calculation of the UV/Vis spectra for the inclusion and the exterior complexes indicated that the charge-transfer band that is often used to predict the formation of the inclusion complexes in solution is, in reality, due to the exterior mode of complexation. These results suggest that UV/Vis spectroscopy is not a reliable method for assigning the complexation modes in TTF:BB 4+ rotaxanes and related systems. A blue box of tricks: The electronic structures and thermodynamic stabilities of complexes of tetrathiafulvalene and cyclobis(paraquat-p-phenylene) (the "blue box") were investigated in the gas-phase by using second-order perturbation theory, MP2. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


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