Injection of photoexcited electrons from colloidal PbS quantum dots into TiO(2) nanoparticles is investigated. The electron affinity and ionization potential of PbS quantum dots, inferred from cyclic voltammetry measurements, show strong size dependence due to quantum confinement. On the basis of the measured energy levels, photoexcited electrons should transfer efficiently from the quantum dots into TiO(2) only for quantum-dot diameter below approximately 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of PbS quantum dots coupled to titanium dioxide nanoparticles are consistent with electron transfer for small quantum dots. The measured electron transfer time is surprisingly slow ( approximately 100 ns), and implications of this for future photovoltaics will be discussed. Initial results obtained from solar cells sensitized with PbS quantum dots are presented.

A facile high-yield synthetic route has been established for the synthesis of R-hydroxy methyl ketones. These intermediates are important precursors to the tricyanovinyldihydrofuran type of acceptor used in high µβ nonlinear optical chromophores. 3-Hydroxy-3-methyl-2-butanone is one of only three commercially available precursors of this type, limiting the chemist from making systematic studies of structure property relationships. This very general synthetic method allows a wide variety of R-hydroxy ketone structures to be easily made.Supporting Information Available: General experimental data: GC/MS analyses of compounds 1-12 and the HPLC analyses of compounds 14-23 (PDF). This material is available free of charge via the Internet at http://pubs.acs.org. CM011734T

We have successfully synthesized several new substituted thiophene-based electro-optic chromophores. All of these chromophores have structures similar to FTC but they incorporated our newly designed tricyanovinyldihydrofuran acceptors. Since these acceptors possess an anisotropic structure, all of the chromophores are very soluble in a wide range of organic solvents. Thermal study of these chromophores by TGA shows all of them are very stable in air. UV spectra indicate the chromophores have a large solvatochromic effect, implying very large molecular nonlinearities.

Four new isophorone and combined isophorone and thiophene bridged chromophores have been synthesized. All of these new high µβ chromophores possess our newly synthesized tricyanovinyldihydrofuran acceptors. Because of our unique acceptor design, all of our chromophores show high solubility in all organic solvents due to minimized chromophorechromophore electrostatic interactions. These chromophores have also been studied with respect to their solvatochromism and thermal behavior by TGA in air. Preliminary EO characterization of one of these chromophores in polycarbonate has demonstrated an extremely high r 33 of 70 pm/V at 1550 nm. We believe that this is the largest r 33 reported at this wavelength.

We report the formation of thin anisotropic phase gratings in a nematic liquid-crystalline film by use of lateral (fringing) electric fields induced by transparent interdigitated electrodes. These gratings yield high diffraction efficiency (>30%) with a strong dependence on the readout beam incidence angle. In addition, the formation of a defect wall is observed that has a significant effect on the diffraction properties of the phase grating.