Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 6 de 6
Filter
Add more filters










Database
Language
Publication year range
1.
J Am Chem Soc ; 134(48): 19820-7, 2012 Dec 05.
Article in English | MEDLINE | ID: mdl-23130681

ABSTRACT

Dye-sensitized solar cells, especially those comprising molecular chromophores and inorganic titania, have shown promise as an alternative to silicon for photovoltaic light-to-electrical energy conversion. Co-sensitization (the use of two or more chromophores having complementary absorption spectra) has attracted attention as a method for harvesting photons over a broad spectral range. If implemented successfully, then cosensitization can substantially enhance photocurrent densities and light-to-electrical energy conversion efficiencies. In only a few cases, however, have significant overall improvements been obtained. In most other cases, inefficiencies arise due to unconstructive energy or charge transfer between chromophores or, as we show here, because of modulation of charge-recombination behavior. Spatial isolation of differing chromophores offers a solution. We report a new and versatile method for fabricating two-color photoanodes featuring spatially isolated chromophore types that are selectively positioned in desired zones. Exploiting this methodology, we find that photocurrent densities depend on both the relative and absolute positions of chromophores and on "local" effective electron collection lengths. One version of the two-color photoanode, based on an organic push-pull dye together with a porphyrin dye, yielded high photocurrent densities (J(SC) = 14.6 mA cm(-2)) and double the efficiency of randomly mixed dyes, once the dyes were optimally positioned with respect to each other. We believe that the organizational rules and fabrication strategy will prove transferrable, thereby advancing understanding of panchromatic sensitization as well as yielding higher efficiency devices.

2.
Langmuir ; 26(3): 1401-4, 2010 Feb 02.
Article in English | MEDLINE | ID: mdl-19911802

ABSTRACT

Two porphyrin-based dyes with carboxylic acid tethers of differing acidity in both protonated and deprotonated forms were examined on ZnO nanotube electrodes. All of the dyes have similar surface coverage, but only the more acidic dye in the acid form injects electrons well; this dye is the only one that corrodes the ZnO. In control experiments on TiO(2) nanoparticle electrodes, both dyes load and inject in protonated and deprotonated forms. These results are consistent with a requirement that the dye must partially corrode the ZnO surface in order for efficient injection to occur. Alternatively, it may possibly point to a coupling of electron injection to proton uptake.

3.
Chem Commun (Camb) ; (16): 1886-8, 2008 Apr 28.
Article in English | MEDLINE | ID: mdl-18401507

ABSTRACT

The structure of a cyclic self-assembled tetramer of an asymmetric meso-ethynylpyridyl-functionalized Zn(II)-porphyrin was established by solution-phase X-ray scattering and diffraction; femtosecond transient absorption and anisotropy spectroscopies were used to (a) observe rapid energy transfer (3.8 ps(-1)) between porphyrin subunits and (b) establish that the transfer occurs between adjacent units.


Subject(s)
Energy Transfer , Porphyrins/chemistry , Cyclization , Models, Molecular , Molecular Structure , Spectrum Analysis , Time Factors
4.
Appl Spectrosc ; 61(8): 832-8, 2007 Aug.
Article in English | MEDLINE | ID: mdl-17716401

ABSTRACT

This paper describes the development of a nanoscale optical pH probe based upon the surface-enhanced Raman scattering (SERS) properties of silica-gold core-shell nanoparticles. In this approach, a thin layer of gold is deposited onto a core of silica to form a metallic nanoshell with surface plasmon modes in the red-to-near-infrared spectral region. The surface of the nanoshell is functionalized with a pH-sensitive SERS reporter molecule, 4-mercaptopyridine (4-MPy). The SERS spectra of 4-MPy is shown to be sensitive to the pH of the surrounding media within the range of 3 to 7. In addition, it is shown that individual silica-gold core-shell nanoparticles yield more reliable SERS spectra than aggregates of core-shell nanoparticles.


Subject(s)
Metal Nanoparticles/chemistry , Nanotechnology/methods , Spectrum Analysis, Raman , Gold/chemistry , Hydrogen-Ion Concentration , Reproducibility of Results , Scattering, Radiation , Silicon Dioxide/chemistry , Surface Plasmon Resonance/methods
5.
Faraday Discuss ; 132: 249-59; discussion 309-19, 2006.
Article in English | MEDLINE | ID: mdl-16833120

ABSTRACT

Single metal nanoparticles and nanoaggregates are known to emit intense bursts of surface-enhanced Raman scattering (SERS) in an intermittent on and off fashion. The characteristic "blinking" timescales range from milliseconds to seconds. Here we report detailed temperature dependence (both heating and cooling) and light-intensity studies to further examine the origins of this intriguing phenomenon. The results indicate that blinking SERS contains both a thermo-activated component and a light-induced component. Several lines of evidence suggest that the observed fluctuations are caused by thermally activated diffusion of individual molecules on the particle surface, coupled with photo-induced electron transfer and structural relaxation of surface active sites or atomic-scale roughness features.


Subject(s)
Nanoparticles , Spectrum Analysis, Raman/methods , Surface Properties , Temperature
6.
J Am Chem Soc ; 126(9): 2676-7, 2004 Mar 10.
Article in English | MEDLINE | ID: mdl-14995165

ABSTRACT

Novel open-framework alkali metal uranyl periodates, having the formula A[(UO2)3(HIO6)(OH)(O)(H2O)].1.5H2O (A = Li, Na, K, Rb, Cs), have been prepared through mild hydrothermal synthesis. These isostructural compounds contain distorted UO7 pentagonal bipyramids that are linked through a uranyl (UO22+) to uranyl cation-cation interaction. This interaction arises from a single axial uranyl oxygen coordinating at an equatorial site of an adjacent uranyl unit. These uranium oxide polyhedra are further bound by IO6 distorted octahedra creating an open-framework structure whose channels contain the alkali metal cations.

SELECTION OF CITATIONS
SEARCH DETAIL
...