Photoinduced Charge Separation In Platinum Acetylide Oligomers

The series of three donor-spacer-acceptor complexes, DPAF-Ptn-NDI, has been synthesized and characterized using time-resolved absorption spectroscopy In these complexes, the donor is a (diphenylamino)-2,7-fluorenylene (DPAF) unit, the acceptor is a naphthalene diimide (NDI), and the spacers are a series of platinum acetylides of varying lengths, [-Pt(PBu(3))(2)C C-Ph-C C-](n) (where Bu = n-butyl Ph = 1,4-phenylene and n = 1 2, and 3) Electrochemistry indicates that the DPAF-Ptn-NDI system has a charge transfer state at ca 1 5 eV above the ground state that is based on one electron transfer from the DPAF donor to the NDI acceptor Transient absorption spectroscopy on time scales ranging from 0 2 ps to 1 mu s reveals that excitation of all of the complexes leads to production of the charge transfer state with nearly unit quantum efficiency The rates for charge separation and charge recombination are not strongly dependent upon the length of the platinum acetylide spacer, suggesting that the spacer is actively involved in the electron (hole) transport processes Analysis of the experimental results leads to a model in which charge separation and charge recombination occur by hole-hopping via states localized on the [-Pt(PBu(3))(2)C C-Ph-C C-](n) bridge

Urban-Rural Gradient Analysis of Amount and Distribution of Carbon and Nitrogen in Soils of Kumasi Region, Ghana

While urbanisation is a global phenomenon, cities in developing countries exhibit particularly high levels of growth in recent years. In Ghana, this phenomenon of rapid growth from 31% of the people living in urban areas in 1984 to 51% urban population in 2010 has created expansive urban forms, impacting natural resources. The aim of this study is to analyse some of the impacts on soils of this rapid urban development. A stratified random sampling design was used to sample soils from 70 maize fields on Acrisols within the area of Kumasi, which was urban already in 1986, and other areas that became urban later. Rural maize fields and forests were also sampled. Three replicates were taken at each site of maize mono-crop and/or mixed-crop subsistence farms to keep consistency. Topsoil samples (0-10 cm depth) were taken volumetrically in 250 cm3 steel cylinders. The samples are currently analysed for soil pH, and for C and N by use of a Leco TruSpec CHN analyser. An ANOVA will be calculated to analyse the differences in means between urban and non-urban areas. A variogram will then be fitted to characterise spatial correlations in the urban to rural continuum of C and N amounts, and consequently mapped out. We hypothesise that C and N contents of soils under maize in urbanised areas of Kumasi exceed those of comparable soils and land-use in adjacent rural areas as reported by Bellwood-Howard et al. 2015, for other West-African cities. Among other reasons, disposal of household waste including organic materials, which is generally practised in urban Ghana due to inadequate waste management, is expected to increase C and N contents. We suggest that urban farms, if well-coordinated into urban planning and management, can provide a viable source of food security to urban dwellers in developing countries. Although analyses of additional parameters are needed pH as well as C and N amounts already provide relevant information on the critical role urbanisation play in the sustainable development of cities in Ghana

Morphology and Oxygen Sensor Response of Luminescent Ir-Labeled Poly(dimethylsiloxane)/Polystyrene Polymer Blend Films

Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir−PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir−PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir−PDMS in PS (ca. 10 wt %), the Ir−PDMS exists as circular domains, with diameters ranging from 2 to 5 μm, surrounded by the majority PS phase. For larger weight fractions of Ir−PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern−Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 μm. The results of this investigation show that the micrometer-sized Ir−PMDS domains display a 2−3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed

Impurity effects on the band structure of one-dimensional photonic crystals: Experiment and theory

We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one dimensional obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes, and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e.g. interstitial, substitutional) and shows that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulas, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penney model.Comment: 16 pages, 7 figure

The Calogero-Moser equation system and the ensemble average in the Gaussian ensembles

From random matrix theory it is known that for special values of the coupling constant the Calogero-Moser (CM) equation system is nothing but the radial part of a generalized harmonic oscillator Schroedinger equation. This allows an immediate construction of the solutions by means of a Rodriguez relation. The results are easily generalized to arbitrary values of the coupling constant. By this the CM equations become nearly trivial. As an application an expansion for in terms of eigenfunctions of the CM equation system is obtained, where X and Y are matrices taken from one of the Gaussian ensembles, and the brackets denote an average over the angular variables.Comment: accepted by J. Phys.

Pressure-sensitive paint measurements in a shock tube

Abstract Surface pressures were measured in the shortduration, transient flow environment of a small-scale, low pressure-ratio shock tube using thin-film pressure-sensitive paint (PSP). Issues regarding coating formulation, measurement uncertainty, optical system design, and temperature and illumination compensation are discussed. The pressure measurements were acquired during steady flow conditions following the passage of normal shocks and expansion regions along a flat sidewall and a wedge sidewall. The PSP characteristic response time was 3 to 6 ms. Overall pressure uncertainty for the shock tube measurements ranged up to 5% over one atmosphere and compared well with theoretical estimates of uncertainty

Negative Polaron And Triplet Exciton Diffusion In Organometallic molecular Wires

The dynamics of negative polaron and triplet exciton transport within a series of monodisperse platinum (Pt) acetylide oligomers is reported. The oligomers consist of Pt-acetylide repeats, [PtL(2)-C C-ph-C C-](n) (where L = PBu(3) and Ph = 1,4-phenylene, n = 2, 3, 6, and 10), capped with naphthalene diimide (NDI) end groups. The Pt acetylide segments are electro- and photoactive, and they serve as conduits for transport of electrons (negative polaron) and triplet excitons. The NDI end groups are relatively strong acceptors, serving as traps for the carriers. Negative polaron transport is studied by using pulse radiolysis/transient absorption at the Brookhaven National Laboratory Laser-Electron Accelerator Facility (LEAF). Electrons are rapidly attached to the oligomers, with some fraction initially residing upon the Pt acetylide chains. The dynamics of transport are resolved by monitoring the spectral changes associated with transfer of electrons from the chain to the NDI end group. Triplet exciton transport is studied by femtosecond-picosecond transient absorption spectroscopy. Near-UV excitation leads to rapid production of triplet excitons localized on the Pt acetylide chains. The excitons transport to the chain ends, where they are annihilated by charge separation with the NDI end group. The dynamics of triplet transport are resolved by transient absorption spectroscopy, taking advantage of the changes in spectra associated with decay of the triplet exciton and rise of the charge-separated state. The results indicate that negative polarons and excitons are transported rapidly, on average moving distances of similar to 3nm in less than 200 ps. Analysis of the dynamics suggests diffusive transport by a site-to-site hopping mechanism with hopping times of similar to 27 ps for triplets and \u3c10 ps for electrons

Green functions for generalized point interactions in 1D: A scattering approach

Recently, general point interactions in one dimension has been used to model a large number of different phenomena in quantum mechanics. Such potentials, however, requires some sort of regularization to lead to meaningful results. The usual ways to do so rely on technicalities which may hide important physical aspects of the problem. In this work we present a new method to calculate the exact Green functions for general point interactions in 1D. Our approach differs from previous ones because it is based only on physical quantities, namely, the scattering coefficients, $R$ and $T$, to construct $G$. Renormalization or particular mathematical prescriptions are not invoked. The simple formulation of the method makes it easy to extend to more general contexts, such as for lattices of $N$ general point interactions; on a line; on a half-line; under periodic boundary conditions; and confined in a box.Comment: Revtex, 9 pages, 3 EPS figures. To be published in PR