Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DIPOLES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Inducing polarity in [VO{sub 3}]{sub n}{sup n-} chain compounds using asymmetric hydrogen-bonding networks

1,4-Bis(3-aminopropyl)piperazine, (R)-3-aminopiperidine and (S)-3-aminopiperidine were used in the syntheses of [C{sub 10}H{sub 26}N{sub 4}][VO{sub 3}]{sub 2}{center_dot}2H{sub 2}O, [(R)-C{sub 5}H{sub 14}N{sub 2}][VO{sub 3}]{sub 2} and [(S)-C{sub 5}H{sub 14}N{sub 2}][VO{sub 3}]{sub 2}, which all contain similar [VO{sub 3}]{sub n}{sup n-} chains. Inversion symmetry within the 1,4-bis(3-aminopropyl)piperazine allows for crystallization of [C{sub 10}H{sub 26}N{sub 4}][VO{sub 3}]{sub 2}{center_dot}2H{sub 2}O in a centrosymmetric space group, while the use of enantiomerically pure sources of either (R)-3-aminopiperidine or (S)-3-aminopiperidine forces crystallographic noncentrosymmetry. Moreover, asymmetry in the hydrogen-bonding networks between the metavanadate chains and either [(R)-3-aminopiperidineH{sub 2}]{sup 2+} or [(S)-3-aminopiperidineH{sub 2}]{sup 2+} cations directs alignment of the chains and crystallization in a polar space group (C2, no. 5). Component and net dipole moments were calculated using iterative-Hirshfeld partial atomic charges. [(R)-C{sub 5}H{sub 14}N{sub 2}][VO{sub 3}]{sub 2} and [(S)-C{sub 5}H{sub 14}N{sub 2}][VO{sub 3}]{sub 2} both display type 1 phase-matching capabilities and exhibit second harmonic generation activities of {approx}140 Multiplication-Sign {alpha}-SiO{sub 2}. - Graphical abstract: One centrosymmetric and a pair of polar noncentrosymmetric templated metavanadates were synthesized under mild hydrothermal conditions. Asymmetry in the hydrogen-bonding between either [(R)-C{sub 5}H{sub 14}N{sub 2}]{sup 2+} or [(S)-C{sub 5}H{sub 14}N{sub 2}]{sup 2+} and [VO{sub 3}]{sub n}{sup n-} chains results in polar structures that exhibit type 1 phase-matching capabilities. Hirshfeld surfaces were used to probe the hydrogen-bonding networks and component and net dipole moments were calculated from atomic positions and iterative-Hirshfeld partial charges. Highlights: Black-Right-Pointing-Pointer One centrosymmetric and a pair of polar templated metavanadate chain compounds are reported. Black-Right-Pointing-Pointer Asymmetry in the hydrogen-bonding networks drives the compound polarities. Black-Right-Pointing-Pointer Iterative-Hirshfeld partitioning was used to calculate partial atomic charges. Black-Right-Pointing-Pointer Net and component dipole moments are calculated for each compound. Black-Right-Pointing-Pointer Type 1 phase-matching behavior and SHG activities of {approx}140 Multiplication-Sign {alpha}-SiO{sub 2} are found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Photophysical properties of donor- N-Ary-Product -acceptor azoic chromophores adsorbed and intercalated into Mg--Al--LDH

Ethyl Orange (EO) and 4-aminoazobenzene-4-sulfonic (AS) anions with Donor- N-Ary-Product -Acceptor structure have been intercalated into the layered double hydroxide (LDH), [Mg{sub 0.66} Al{sub 0.34} (OH){sub 2}] (CO{sub 3}){sub 0.17}{center_dot}0.67H{sub 2}O or adsorbed on the external surface of the host by the method of ion-exchange procedures. The photoabsorption and fluorescence properties of the obtained compounds were different from the pure solid phase of EO and AS. It was suggested that the photophysical properties of guests were closely related to the geometry and electrical structure of the guest molecule, which can affect the distribution and orientation of the guests in the layers or on the surface of the host. The host-guest interactions modulate photophysical properties of guest. In addition, the guest having higher molecular dipole moments surface exchanged on Mg--Al--CO{sub 3}--LDH are beneficial to the enhancement of the blue emission than that of intercalation into LDH. - Graphical abstract: Emission spectra of (a) EO (b) EO surface exchanged on Mg--Al--CO{sub 3}--LDH (c) Mg--Al--EO--LDH. Emission spectra of (a) AS (b) Mg--Al--AS--LDH (c) AS surface exchanged on Mg--Al--CO{sub 3}--LDH. The guests having higher molecular dipole moments surface exchanged on Mg--Al--CO{sub 3}--LDH are beneficial to the enhancement of the blue emission than that of intercalation into LDH. Highlights: Black-Right-Pointing-Pointer EO and AS are intercalated into LDHs or adsorbed on the external surface of LDHs. Black-Right-Pointing-Pointer The host-guest interactions modulate photophysical properties of the guest. Black-Right-Pointing-Pointer The guests having higher molecular dipole moments can enhance the blue emission.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structure and photoluminescence properties of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} phosphors for solid-state lighting application

Novel phosphors of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+} and Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce{sup 3+} emission properties and the crystal structure of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7} is built and the result shows that Ce{sup 3+} ions occupy two non-equivalent Y{sup 3+} sites in the host. The codoping of Tb{sup 3+} in Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+} can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce{sup 3+}→Tb{sup 3+}. The energy transfer processes of Ce{sup 3+}–Ce{sup 3+} and Ce{sup 3+}–Tb{sup 3+} are analysed and determined to be electric dipole–dipole and dipole–quadrupole, respectively. The broad PLE spectra of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+} and Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs. - Graphical abstract: Colour-tunable phosphors Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} with optimal quantum yield of 75.2% are synthesized and the phosphors can be served as n-UV pumped materials for LEDs. - Highlights: • Green phosphor Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} with quantum efficiency of 75.2% for n-UV application is synthesized. • The site occupation of Ce{sup 3+} in Na{sub 2}Y{sub 2}B{sub 2}O{sub 7} is investigated with the crystal structure and photoluminescence spectra. • The energy transfer of Ce{sup 3+}–Ce{sup 3+} and Ce{sup 3+}–Tb{sup 3+}, which is responsible to the tunable emitting colour of the phosphor, is demonstrated and the mechanism is studied.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Bandgap engineering in van der Waals heterostructures of blue phosphorene and MoS{sub 2}: A first principles calculation

Blue phosphorene (BP) was theoretically predicted to be thermally stable recently. Considering its similar in-layer hexagonal lattice to MoS{sub 2}, MoS{sub 2} could be an appropriate substrate to grow BP in experiments. In this work, the van der Waals (vdW) heterostructures are constructed by stacking BP on top of MoS{sub 2}. The thermal stability and electronic structures are evaluated based on first principles calculations with vdW-corrected exchange-correlation functional. The formation of the heterostructures is demonstrated to be exothermic and the most stable stacking configuration is confirmed. The heterostructures BP/MoS{sub 2} preserve both the properties of BP and MoS{sub 2} but exhibit relatively narrower bandgaps due to the interlayer coupling effect. The band structures can be further engineered by applying external electric fields. An indirect–direct bandgap transition in bilayer BP/MoS{sub 2} is demonstrated to be controlled by the symmetry property of the built-in electric dipole fields. - Graphical abstract: An indirect-direct band gap transition occurs in van der Waals heterostructure of MoS{sub 2}/BP under external electric fields which is demonstrated to be controlled by the symmetry of the built-in electric dipole fields. - Highlights: • The stacking of heterostructures of BP/MoS{sub 2} is demonstrated to be exothermic. • This suggests that it is possible to grow BP using MoS{sub 2} as the substrate. • The band structures of the heterostructures are exploited. • It realizes an indirect–direct gap transition under external electric fields. • The symmetry of the built-in electric dipole fields controls such gap transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Identification of Brillouin Zones by In-Plane Lasing from Light-Cone Surface Lattice Resonances

Periodic optical structures can control the flow of light, which has facilitated applications in optical fibers, laser cavities, and biochemical sensors. The first Brillouin zone (BZ) in reciprocal space can describe all the electromagnetic fields localized inside a photonic lattice. However, photonic lattices also exhibit radiative losses from light scattering, but the radiated fields are not captured by the first BZ. In a two-dimensional lattice, the in-plane wavevectors of photonic modes are limited by the so-called light cone, which depicts free-photon dispersion relations in the surrounding medium. Here we show that projection of the light cone on extended BZs provides a geometric method to observe radiated electromagnetic fields of photonic lattice modes. We developed a coupled dipole radiation theory to reveal how lattice geometry and dipole orientation affect the angular distributions of the radiated fields. Using dye molecules as local dipole emitters to excite and probe the optical modes, we experimentally identified high-order BZ edges through directional, in-plane lasing emission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Molecular Dynamics Simulation of Tri-n-Butyl-Phophate Liquid: A Force Field Comparative Study

Molecular dynamics (MD) simulations were conducted to compare the performance of four force fields in predicting thermophysical properties of tri-n-butyl-phosphate (TBP) in the liquid phase. The intramolecular force parameters used were from the Assisted Model Building with Energy Refinement (AMBER) force field model. The van der Waals parameters were based on either the AMBER or the Optimized Potential for Liquid Simulation (OPLS) force fields. The atomic partial charges were either assigned by performing quantum chemistry calculations or utilized previously published data, and were scaled to approximate the average experimental value of the electric dipole moment. Canonical ensemble computations based on the aforementioned parameters were performed near the atmospheric pressure and temperature to obtain the electric dipole moment, mass density, and self-diffusion coefficient. In addition, the microscopic structure of the liquid was characterized via pair correlation functions between selected atoms. It has been demonstrated that the electric dipole moment can be approximated within 1% of the average experimental value by virtue of scaled atomic partial charges. The liquid mass density can be predicted within 0.5-1% of its experimentally determined value when using the corresponding charge scaling. However, in all cases the predicted self- diffusion coefficient is significantly smaller than a commonly quoted experimental measurement; this result is qualified by the fact that the uncertainty of the experimental value was not available.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Experiments and Theory of Dusty Plasmas

The purpose of this paper is to present the most important theoretical and experimental discoveries that have been made in the area of dusty plasma physics. We describe the physics and observations of the well celebrated dust acoustic wave (DAW) and the dust ion-acoustic wave (DIAW) in dusty plasmas with weakly coupled dust grains, as well as the dust Coulomb crystal and dust lattice oscillations (DLOs) in dusty plasmas with strongly coupled dust grains. In dusty plasmas, the dust charge fluctuation is a dynamical variable, which provides a novel collisionless damping of the DA and DIA waves. The latter and the DLOs are excited by external sources, which are here discussed. Besides the Debye-Hueckel short-range repulsive force between like charged dust grains, there are novel attractive forces (e.g. due to dipole-dipole dust particle interactions, overlapping Debye spheres, ion focusing and ion wakefields, dipole magnetic moments etc.), which provide unique possibilities for attracting charged dust particles of similar polarity. The dust particle attraction is responsible for the formation of dust Coulomb crystals in laboratory dusty plasmas, as well as for the formation of planets and large astrophysical bodies in the Milky Way galaxy and in interstellar media. Furthermore, the nonlinear DAW, DIAW, and DLOs also appear in the form of solitary and shock waves, the physics and observations of which are briefly discussed. Finally, we discuss possible applications of dust-in-plasmas and dusty plasmas in laboratory and space.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

The mechanism of emerging catalytic activity of gold nano-clusters on rutile TiO{sub 2}(110) in CO oxidation reaction

This paper reveals the fact that the O adatoms (O{sub ad}) adsorbed on the 5-fold Ti rows of rutile TiO{sub 2}(110) react with CO to form CO{sub 2} at room temperature and the oxidation reaction is pronouncedly enhanced by Au nano-clusters deposited on the above O-rich TiO{sub 2}(110) surfaces. The optimum activity is obtained for 2D clusters with a lateral size of {approx}1.5 nm and two-atomic layer height corresponding to {approx}50 Au atoms/cluster. This strong activity emerging is attributed to an electronic charge transfer from Au clusters to O-rich TiO{sub 2}(110) supports observed clearly by work function measurement, which results in an interface dipole. The interface dipoles lower the potential barrier for dissociative O{sub 2} adsorption on the surface and also enhance the reaction of CO with the O{sub ad} atoms to form CO{sub 2} owing to the electric field of the interface dipoles, which generate an attractive force upon polar CO molecules and thus prolong the duration time on the Au nano-clusters. This electric field is screened by the valence electrons of Au clusters except near the perimeter interfaces, thereby the activity is diminished for three-dimensional clusters with a larger size.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Linear and nonlinear studies of velocity shear driven three dimensional electron-magnetohydrodynamics instability

The study of electron velocity shear driven instability in electron magnetohydrodynamics (EMHD) regime in three dimensions has been carried out. It is well known that the instability is non-local in the plane defined by the flow direction and that of the shear, which is the usual Kelvin-Helmholtz mode, often termed as the sausage mode in the context of EMHD. On the other hand, a local instability with perturbations in the plane defined by the shear and the magnetic field direction exists which is termed as kink mode. The interplay of these two modes for simple sheared flow case as well as that when an external magnetic field exists has been studied extensively in the present manuscript in both linear and nonlinear regimes. Finally, these instability processes have been investigated for the exact 2D dipole solutions of EMHD equations [M. B. Isichenko and A. N. Marnachev, Sov. Phys. JETP 66, 702 (1987)] for which the electron flow velocity is sheared. It has been shown that dipoles are very robust and stable against the sausage mode as the unstable wavelengths are typically longer than the dipole size. However, we observe that they do get destabilized by the local kink mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Resonance zones and quasi-linear diffusion coefficients for radiation belt energetic electron interaction with oblique chorus waves in the Dungey magnetosphere

The resonance regions for resonant interactions of radiation belt electrons with obliquely propagating whistler-mode chorus waves are investigated in detail in the Dungey magnetic fields that are parameterized by the intensity of uniform southward interplanetary magnetic field (IMF) Bz or, equivalently, by the values of D=(M/B{sub z,0}){sup 1/3} (where M is the magnetic moment of the dipole and B{sub z,0} is the uniform southward IMF normal to the dipole's equatorial plane). Adoption of background magnetic field model can considerably modify the determination of resonance regions. Compared to the results for the case of D = 50 (very close to the dipole field), the latitudinal coverage of resonance regions for 200 keV electrons interacting with chorus waves tends to become narrower for smaller D-values, regardless of equatorial pitch angle, resonance harmonics, and wave normal angle. In contrast, resonance regions for 1 MeV electrons tend to have very similar spatial lengths along the field line for various Dungey magnetic field models but cover different magnetic field intervals, indicative of a strong dependence on electron energy. For any given magnetic field line, the resonance regions where chorus-electron resonant interactions can take place rely closely on equatorial pitch angle, resonance harmonics, and kinetic energy. The resonance regions tend to cover broader latitudinal ranges for smaller equatorial pitch angles, higher resonance harmonics, and lower electron energies, consistent with the results in Ni and Summers [Phys. Plasmas 17, 042902, 042903 (2010)]. Calculations of quasi-linear bounce-averaged diffusion coefficients for radiation belt electrons due to nightside chorus waves indicate that the resultant scattering rates differ from using different Dungey magnetic field models, demonstrating a strong dependence of wave-induced electron scattering effect on the adoption of magnetic field model. Our results suggest that resonant wave-particle interaction processes should be implemented into a sophisticated, accurate global magnetic field model to pursue comprehensive and complete models of radiation belt electron dynamics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Chirped-pulse millimeter-wave spectroscopy: Spectrum, dynamics, and manipulation of Rydberg-Rydberg transitions

We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg-Rydberg transitions is that they have enormous electric dipole transition moments ({approx}5 kiloDebye at n*{approx} 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70-84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is {approx}100 kHz. Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Non-linear QCD dynamics in two-photon interactions at high energies

Assuming that the dipole - dipole cross section can be related with the dipole - proton cross section, we calculate the total {gamma}{gamma}, {gamma}*{gamma}* cross-sections and the real photon structure function F{sup {gamma}}{sub 2}(x,Q{sup 2}) using the recent solution of the BK equation with running coupling constant.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Near-field heat transfer between gold nanoparticle arrays

The radiative heat transfer between gold nanoparticle layers is presented using the coupled dipole method. Gold nanoparticles are modelled as effective electric and magnetic dipoles interacting via electromagnetic fluctuations. The effect of higher-order multipoles is implemented in the expression of electric polarizability to calculate the interactions at short distances. Our findings show that the near-field radiation reduces as the radius of the nanoparticles is increased. Also, the magnetic dipole contribution to the heat exchange becomes more important for larger particles. When one layer is displayed in parallel with respect to the other layer, the near-field heat transfer exhibits oscillatory-like features due to the influence of the individual nanostructures. Further details about the effect of the nanoparticles size are also discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Negative-U centers as a basis of topological edge channels

We present the findings of the studies of the silicon sandwich nanostructure that represents the high mobility ultranarrow silicon quantum well of the p-type (Si-QW), 2 nm, confined by the δ-barriers, 3 nm, heavily doped with boron on the n-type Si (100) surface. The ESR studies show that nanostructured δ-barriers confining the Si-QW consist predominantly of the dipole negative-U centers of boron, which are caused by the reconstruction of the shallow boron acceptors along the <111> crystallographic axis, 2B{sup 0}→B{sup +}+B{sup −}. The electrically ordered chains of dipole negative-U centers of boron in the δ-barriers appear to give rise to the topological edge states separated vertically, because the value of the longitudinal, G{sub xx} = 4e{sup 2}/h, and transversal, G{sub xy} = e{sup 2}/h, conductance measured at extremely low drain-source current indicates the exhibition of the Quantum Spin Hall effect. Besides, the Aharonov-Casher conductance oscillations and the “0.7⋅(2e{sup 2}/h)-feature” obtained are evidence of the interplay of the spontaneous spin polarisation and the Rashba spin-orbit interaction that is attributable to the formation of the topological edge channels. We discuss the phenomenological model of the topological edge channel which can demonstrate the ballistic, Aharonov-Chasher effect or Josephson junction behaviour in dependence on the disorder in the distribution of the negative-U dipole centers in the upper and down d-barriers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Design, development, and acceleration trials of radio-frequency quadrupole

A deuteron radio frequency quadrupole (RFQ) accelerator has been designed, fabricated, and tested at BARC, which will be used for neutron generation. The RFQ operates at a frequency of 350 MHz and needs an inter-vane voltage of 44 kV to accelerate the deuteron beam to 400 keV within a length of 1.03 m. The error analysis shows that the offset of two opposite vanes in the same direction by 100 μm leads to a change in resonant frequency by 1.3 MHz and a significant change of fields in the quadrants (∼±40% with respect to average field). From the 3D analysis, we have observed that the unwanted dipole mode frequencies are very near to the quadrupole mode frequency which will make structure sensitive to the perturbations. In order to move the dipole modes away from the quadrupole modes, we have used the dipole stabilizer rods. The 5 wire transmission line theory was used to study the perturbative analysis of the RFQ and based on this a computer program has been written to tune the cavity to get required field distribution. Based on these studies, a 1.03 m long RFQ made of OFE copper has been fabricated and tested. Even though the RFQ was designed for deuteron (D{sup +}) beam, we tested it by accelerating both the proton (H{sup +}) and D{sup +} beams. The RFQ was operated in pulsed mode and accelerated both H{sup +} and D{sup +} beams to designed values of 200 and 400 keV, respectively. The measured parameters are in good agreement with the designed values validating our simulations and fabrication processes. In this paper, simulations, RF measurements, and beam commissioning results are presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Quantum mechanical/molecular mechanical/continuum style solvation model: Second order Møller-Plesset perturbation theory

A combined quantum mechanical/molecular mechanical/continuum (QM/MM/C) style second order Møller-Plesset perturbation theory (MP2) method that incorporates induced dipole polarizable force field and induced surface charge continuum solvation model is established. The Z-vector method is modified to include induced dipoles and induced surface charges to determine the MP2 response density matrix, which can be used to evaluate MP2 properties. In particular, analytic nuclear gradient is derived and implemented for this method. Using the Assisted Model Building with Energy Refinement induced dipole polarizable protein force field, the QM/MM/C style MP2 method is used to study the hydrogen bonding distances and strengths of the photoactive yellow protein chromopore in the wild type and the Glu46Gln mutant.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C{sub 60} molecular triad

We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C{sub 60} (CPC{sub 60}) molecular triad. The chain-like molecular triad undergoes photoinduced charge transfer process exhibiting a large excited state dipole moment, making it suitable for application to molecular-scale opto-electronic devices. An important consideration is that the structural flexibility of the CPC{sub 60} triad impacts its dynamics in solvents. Since experimentally measured dipole moments for the triad of ∼110 D and ∼160 D strongly indicate a range in structural variability in the excited state, studying the effect of structural changes on the CT excited state energetics furthers the understanding of its charge transfer states. We have calculated the variation in the lowest CT excited state energies by performing a scan of possible variation in the structure of the triad. Some of these configurations were generated by incrementally scanning a 360° torsional (dihedral) twist at the C{sub 60}-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC{sub 60} conformations were studied to determine the effect of pi-conjugation and particle-hole Coulombic attraction on the CT excitation energies. Our calculations show that configurational changes in the triad induces a variation of ∼0.6 eV in CT excited state energies in the gas-phase. The corresponding calculated excited state dipoles show a range of 47 D–188 D. The absorption spectra and density of states of these structures show little variation except for the structures where the porphyrin and aryl conjugation is changed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Nanostructured double-layer FeO as nanotemplate for tuning adsorption of titanyl phthalocyanine molecules

The growth, structure of Pt(111) supported double-layer FeO and the adsorption of titanyl phthalocyanine (TiOPc) molecules with tunable site and orientation were presented. According to the atomic-resolution STM image, the structure was rationalized as (8√3 × 8√3) R30°/Pt(111) nanostructure constructed by Fe species coordinated with different number of oxygen on top of non-rotated (8 × 8) FeO /Pt(111) structure. Due to the modulation of the stacking of Fe atoms in the second layer relative to the O atoms in the second layer and the underlying layer, the interface and total dipole moment periodically vary within (8√3 × 8√3) R30°/Pt(111) structure. The resulted periodically distributed dipole-dipole interaction benefits the growth of TiOPc molecules with area-selective sites and molecular orientations. Thus, this study provides a reliable method to govern the adsorption process of the polar molecules for potential applications in future functional molecular devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗