This PDF file contains the front matter associated with SPIE Proceedings Volume 8098, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

In addition to the size dependent optical and electronic properties of semiconductor quantum dots (QDs), quantum confinement also affects the charge separation and recombination dynamics in QD - charge acceptor complexes. It leads to enhanced amplitudes of electron and hole wave functions at the surface, enabling ultrafast interfacial charge transfer, an important property for the application of QDs in photovoltaic and photocatalytic devices. In this proceeding, we show that both charge separation and recombination are ultrafast in strongly quantum confined PbS QDs adsorbed with electron acceptors. Using CdSe/ZnS type I and CdTe/CdSe type II core/shell QDs as model systems, we show that the spatial distributions of electron and wave functions can be optimized to simultaneously achieve ultrafast charge separation and retard charge recombination.

In this proceeding, transient 2D IR spectroscopy is used to study Re dye sensitized TiO₂ nanocrystalline thin films. Multiple conformations of the dye on the interfaces are found by equilibrium 2D IR spectrum and transient 2D IR spectrum indicates these different binding conformations have different electron transfer kinetics.

The temperature- and frequency-dependent ac conductivity of nanoporous metal-oxide semiconductors commonly used in technologies for solar photoconversion is analyzed by using a model based on fluctuation-induced tunneling conduction (FITC). The model takes into account voltage fluctuations of potential barriers that limit electron transport at nanoparticle contact junctions. In contrast to previous models, quantitative agreement over the entire temperature range studied is found by using the FITC model based on a single set of parameters. Guidelines for the design of new materials for dye-sensitized solar cells (DSSCs) and solar photocatalysis are discussed.

Measurements of transient photoconductivity and the cell spectral response provide information about the carrier mobility, recombination mechanisms and the electronic structure in bulk heterojunction solar cells. The presence of band tail states is deduced from the dispersive transport and from the low energy spectral response, which give a consistent values for the slope of the band tail. An approximate density of states distribution is developed by combining data for the band tails, the band edges and the deep states, based on these results along with other information. Measurements show that geminate recombination is not a dominant recombination process in P3HT:PCBM or PCDTBT:PCBM cells. Instead, it is argued that there is good evidence that recombination through interface traps is important.

We have previously shown that regioregularity (i.e., the percentage of head-to-tail linkages between monomer units in the polymer backbone) is a critical factor which determines the morphology of poly(3- hexylthiophene) (P3HT) even at the single chain level. Here, we examined the excitation wavelength dependence on the fluorescence polarization anisotropy of single regioregular (rr-) and regiorandom (rra-) P3HT. For both rr- and rra-P3HT chains, the observed anisotropy is higher as the longer wavelength is used to excite single polymer chains. This indicates that chromophores with longer conjugation length are predominantly located in more highly ordered regions of the chain. However, at any excitation wavelength, the difference between rr- and rra-P3HT is observed. Single rr-P3HT chains fold into highly ordered conformation while rra-P3HT chains assume a wide variety of conformations from isotropic to anisotropic. These new results further support that regioregularity is important for P3HT even at the single chain level and give deeper insights of polymer morphology and its effect on optical property.

In this work we present our new experimental and theoretical results upon investigations of the photoinduced tautomerism processes of single metal-free porphyrin-type molecules. During tautomerization a molecule changes its structure, therefore the excitation transition dipole moment (TDM) of the molecule changes its orientation. Using confocal microscopy in combination with azimuthally and radially polarized laser beams we are able to determine the orientation of the TDM as well as the orientation of a single molecule itself. In the case of tautomerism we are able to visualize this process and even the involved isomers separately. The study first focuses on two symmetrical compounds: a phthalocyanine and a porphyrin. Additionally, differences of the single molecules embedded in a polymer matrix or just spin-coated on a glass cover slide and under nitrogen flow are investigated. In the latter case we observe a higher frequency of the change of the TDM orientation. The experimental studies are supplemented by quantum chemical calculations. Variations of the molecular substituents, the environment and excitation wavelength can give new insights into the excited-state tautomerism process of a single molecule. We also introduce some suggestions for future experiments to support the understanding of the photoinduced tautomerism.

In organic photovoltaic diodes, singlet intrachain excitons dissociate into geminate polaron pairs (GPP) at the heterojonction, which further dissociate into photocarriers or relax into charge transfer exciton (CTX) states. Our temperature-dependent, time-resolved spectroscopic approach unravels the dynamics of those species in films of polycarbazole/fullerene derivative blend. We find that GPP act as a dark reservoir that feeds the CTX. At low temperature, the GPP are trapped and feed the CTX via tunneling, but not the free photocarriers. At room temperature, some of the GPP can overcome the Coulomb barrier and feed the CTX promptly, or be deeply trapped and feed the CTX on several timescales. We find that at room temperature, 16% of the geminate recombination is accounted for by trapped geminate polaron pairs.

This paper was presented at the SPIE conference indicated above and has been withdrawn from publication at the request of the authors.

Modeling methane oxidation reaction in flow conditions regarding heterogeneous radical stages had been carried out. On the basis of the scheme of methane oxidation, the short model of chain radical process was chosen. Oscillation regimes of methane oxidation were studied. It was shown, that the character of oscillation dependent on values of rates of heterogeneous stages of CH₃O₂ radicals destruction and their interaction with inhibitor of process - CH₂O. On the basis of obtained results it has been concluded, that heterogeneous radical stages affect on character of dynamic regimes of process.

The increasing demand for clean, efficient energy has strongly influenced the direction of nanoscale research. One of the most promising areas of solar energy production lies with cadmium selenide quantum dots (CdSe QDs). As a means to improve the efficiency of solar energy conversion in QDs, metal nanoparticles have been examined. It has been shown that in certain systems the presence of these metal nanoparticles increase electron - hole charge separation thus providing extended times for electron harvesting. Most of the systems currently explored utilize gold nanoparticles, which is unsurprising due to the vast amount of synthetic methods for these particles and their plasmonic effects on the QDs. We seek to further examine these unique metal nanoparticle -quantum dot interactions through the study of CdSe QD - palladium nanoparticle systems. We employ both steady-state and time resolved ensemble fluorescence spectroscopy to observe the effects of increasing palladium nanoparticle concentrations on both the fluorescence intensity and lifetime of various CdSe QDs. We find that decreasing separation distance between the particles through increasing palladium concentration, leads to a stronger interaction between the particles. We find expected fluorescence quenching of the QDs at higher concentrations of palladium. At low palladium concentrations however we observe a unique fluorescence enhancement of the QDs. We use this data to explore the relative contributions of energy and electron transfer between the particles and determine the conditions under which the maximum effects of these interactions are observed.

Palladium-based nanomaterials with high surface areas have been receiving great attention due to their unique properties, which enable a number of impressive applications in catalysis, fuel cells, hydrogen storage and chemical sensors. Recent studies have shown that the electrocatalytic performance of Pd-based nanomaterials is highly dependent on the composition, morphology and surface conditions of the synthesized materials. In this study, a variety of Pd-based nanostructured materials including nanoporous Pd networks and PdPt nanodendrites with different compositions have been synthesized using the hydrothermal method. The as-fabricated Pd-based nanostructured materials were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS. The electrochemical properties of these Pd-based nanomaterials were studied using cyclic voltammetry and in-situ electrochemical infrared spectroscopy. Our studies have shown that the fabricated Pd-based nanostructures possess a very large surface area and high catalytic activity towards the electrochemical oxidation of formic acid. In addition, this work has demonstrated that in-situ electrochemical infrared spectroscopy is a powerful technique for the study of the nanostured interface.

Quantum dot applications are numerous and range from photovoltaic devices and lasers, to bio labeling. Complexities in the electronic band structure of quantum dots create the necessity for analysis techniques that can accurately and reproducibly provide their absolute band energies. Cyclic voltammetry (CV) is a novel candidate for these studies and has the potential to become a useful tool in engineering new nanocrystal technology, by providing information necessary for predicting and modeling interfacial charge transfer to and from quantum dots. Advancing from previous reports of nanocrystal CV, a carbon paste electrode was utilized in an attempt to increase measured current by ensuring intimate contact between nanocrystals and the electrode. Our goal was to investigate band energies and model nanocrystal-molecule electron transfer systems.

We have developed a novel route to highly luminescent Cd-free core-shell nanocrystals. By simply refluxing assynthesized CuInS2 nanocrystals with zinc acetate and palmitic acid, highly luminescent CuInS2/ZnS nanocrystals were synthesized. We modified the photoluminescence of the grown nanocrystal by alloying foreign atoms. Nanocrystals with alloyed cores were synthesized by adding selenium and nanocrystals with alloyed shell layers were synthesized by refluxing the as-synthesized CuInS2 nanocrystals with mixture of cadmium acetate, zinc acetate and palmitic acid. It was found that the emission wavelength of the nanocrystals was shifted to longer wavelength side by alloying. The photoluminescence spectra showed clear red-shift without significant minimization of emission intensity. A Detailed study on the emission process of nanocrystals implies that the formation of shell layers with small lattice mismatch minimized mismatch strain generated from the shell layers in contrast to core alloyed nanocrystals.

One of the alternatives to the existing medicines and treatment procedures in fighting multi drug resistance (MDR) is strengthening the effects of medicines by modifying their molecular structures through exposure to laser radiation. A method associated with this, is the generation of micro-droplets which contain medicines solutions; the droplets are utilized/produced as vectors to transport the medicines to targets. In our studies we try to combine these two methods in order to obtain a new technique to deliver the efficient medicines to targets that can be applied for a relative large number of chemicals. For this purpose we have developed an experimental set-up containing a liquid droplets generator, a tunable laser source used to irradiate droplets, a subunit to measure the laser induced fluorescence (LIF) signals and a real time recording system for droplet image analysis. Measurements on different probes, like ultrapure water, commercial grade medicines, newly developed medicines and laser dyes were performed.. All these measurements were performed on waterbased solutions. We present in this paper the laser induced fluorescence measurements results on medicine solutions (in bulk or in a micro-droplet form) that exhibit important modifications after the exposure at laser radiation. It was evidenced that the exposures to laser beams/coherent optical radiation of some medicines solutions in ultrapure water may produce molecular modifications in solutions. These slight modifications of the molecules made them more efficient against bacteria strains.

We present the results on the structure and the optical properties of noble metal (Ag, Au) and oxide (ZnO) nanoparticles synthesized by various methods in different polysaccharide matrices such as chitosan, glycogen, alginate and starch. The structure of the obtained nanoparticles was studied in detail with microscopic techniques (TEM, SEM), while the XPS spectroscopy was used to investigate the effects at the nanoparticle-biomolecule interfaces. The antimicrobial activity of the nanocomposite films with Ag nanoparticles was tested against the Staphylococcus aureus, Escherichia coli and Candida albicans pathogens. In addition, we will present the results on the structure and optical properties of the tryptophan amino acid functionalized silver nanoparticles dispersed in water soluble polymer matrices.