Gerald J. Meyer

MLCT excited states of cuprous bis-phenanthroline coordination compounds

Cuprous bis-phenanthroline compounds possess metal-to-ligand charge transfer, MLCT, excited states. Phenanthroline ligands coordinated to Cu(I) that are disubstituted in the 2- and 9-positions with alkyl or aryl groups, abbreviated CuI(phen′)2+, have long-lived excited states at room temperature. The parent CuI(phen)2+ compound is non-emissive under the same conditions with a short excited state lifetime, τ<10 ns. Disubstitution in the 2,9-positions stabilizes the Cu(I) state and increases the energy gap between the MLCT and the ground state. The prototypical and most well studied compound is CuI(dmp)2+, where dmp is 2,9-(CH3)2-1,10-phenanthroline. In dichloromethane solution at room temperature, CuI(dmp)2+ displays broad MLCT absorption with λmax=454 nm, a broad unstructured emission with λmax=730 nm, and an excited state lifetime of 85 ns. The emission arises from two closely spaced MLCT excited states, separated in energy by 1800 cm−1, that behave as one state at room temperature. CuI(dmp)2+* excited states are quenched in the presence of Lewis bases and coordinating solvents. A 5-coordinate excited state complex, or exciplex, is proposed to account for temperature dependent quenching data. The substantial inner-sphere reorganizational energy changes that follow light excitation are novel features of these MLCT excited states. This review attempts to cover all the existing data reported on CuI(phen′)2+ excited states and contrast it with well-known MLCT behavior of (dπ)6 transition metal compounds.

Biological applications of high aspect ratio nanoparticles

This review describes recent advances in nanomaterials fabrication that have led to the synthesis of high aspect ratio particles on nanometer length scales. The elongated structure of these materials often result in inherent chemical, electrical, magnetic, and optical anisotropy that can be exploited for interactions with cells and biomolecules in fundamentally new ways. We briefly describe the synthetic procedures that have been developed to fabricate nanorods, nanowires, and nanotubes. We summarize literature reports that describe the use of high aspect ratio nanoparticles for biological sensing, separations, and gene delivery. We emphasize the recent discovery of single nanowire field-effect transistors that may revolutionize biological sensing and yield extremely low detection limits. Separations technology with chemically modifiable nanotube membranes and with magnetic nanowires that can be tailored to selectively interact with molecules of interest is also described. Other areas of biotechnology that have been improved by the integration of high aspect ratio nanoparticles are also described.

Magnetic trapping and self-assembly of multicomponent nanowires

Magnetic nanowires suspended in fluid solutions can be assembled and ordered by taking advantage of their large shape anisotropy. Magnetic manipulation and assembly techniques are demonstrated, using electrodeposited Ni nanowires, with diameter 350 nm and length 12 μm. Orienting suspended nanowires in a small magnetic field H≈10 G promotes self-assembly of continuous chains that can extend over several hundred μm. The dynamics of this process can be described quantitatively in terms of the interplay of magnetic forces and fluid drag at low Reynolds number. In addition, a new technique of magnetic trapping is described, by which a single magnetic nanowire can be captured between lithographically patterned magnetic microelectrodes. The use of three-segment Pt–Ni–Pt nanowires yields low resistance, Ohmic electrical contacts between the nanowires and the electrodes. This technique has potential for use in the fabrication and measurement of nanoscale magnetic devices.

Cell manipulation using magnetic nanowires

The use of magnetic nanowires is demonstrated as a method for the application of force to mammalian cells. Magnetic separations were carried out on populations of NIH-3T3 mouse fibroblast cells using ferromagnetic Ni wires 350 nm in diameter and 35 μm long. Separation purities in excess of 90% and yields of 49% are obtained. The nanowires are shown to outperform magnetic beads of comparable volume.

Biological applications of multifunctional magnetic nanowires (invited)

Magnetic particles that can be bound to cells and biomolecules have become an important tool for the application of force in biology and biotechnology. Multifunctional magnetic nanowires fabricated by electrochemical deposition in nanoporous templates are a type of magnetic carrier that offers significant potential advantages over commercially available magnetic particles. Recent experimental work aimed at developing these wires for this purpose is reviewed. Results on chemical functionalization of Au and Au/Ni wires and magnetic manipulation of wires in suspension are described. Fluorescence microscopy was used to demonstrate the covalent binding of thiol-terminated porphyrins to Au nanowires, and to optimize functionalization of two-segment gold–nickel nanowires for selectivity and stability of the nanowire–molecule linkages. Magnetic trapping is a technique where single nanowires are captured from fluid suspension using lithographically patterned micromagnets. The influence of an external magnetic fiel...

Finding the Way to Solar Fuels with Dye-Sensitized Photoelectrosynthesis Cells

The dye-sensitized photoelectrosynthesis cell (DSPEC) integrates high bandgap, nanoparticle oxide semiconductors with the light-absorbing and catalytic properties of designed chromophore-catalyst assemblies. The goals are photoelectrochemical water splitting into hydrogen and oxygen and reduction of CO2 by water to give oxygen and carbon-based fuels. Solar-driven water oxidation occurs at a photoanode and water or CO2 reduction at a cathode or photocathode initiated by molecular-level light absorption. Light absorption is followed by electron or hole injection, catalyst activation, and catalytic water oxidation or water/CO2 reduction. The DSPEC is of recent origin but significant progress has been made. It has the potential to play an important role in our energy future.

Atomic Level Resolution of Dye Regeneration in the Dye-Sensitized Solar Cell

Two donor-acceptor organic dyes have been synthesized that differ only by a two-heteroatom change from oxygen to sulfur within the donor unit. The two dyes, (E)-3-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid (Dye-O) and (E)-3-(5-(4-(bis(4-(hexylthio)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid) (Dye-S), were tested in solar cell devices employing both I(3)(-)/I(-)-based and [Co(bpy)(3)](3+/2+) redox mediators. Power conversion efficiencies over 6% under simulated AM 1.5 illumination (1 Sun) were achieved in both electrolytes. Despite similar optical and redox properties for the two dyes, a consistently higher open-circuit voltage (V(oc)) was measured for Dye-S relative to Dye-O. The improved efficiency observed with Dye-S in an iodide redox mediator is against the commonly held view that sulfur atoms promote charge recombination attributed to inner-sphere interactions. Detailed mechanistic studies revealed that this is a consequence of a 25-fold enhancement of the regeneration rate constant that enhances the regeneration yield under open circuit conditions. The data show that a high short circuit photocurrent does not imply optimal regeneration efficiency as is often assumed.

Electron and energy transfer from CuI MLCT excited states

Abstract Electron and energy transfer processes from CuI MLCT excited states are reviewed. New results demonstrate clearly that these excited states undergo oxidative electron transfer quenching and energy transfer processes. The yields and dynamics of these processes have been spectroscopically quantified. Interfacial electron transfer from CuI MLCT excited states to wide band gap semiconductors has been observed. When utilized in photoelectrochemical cells, this interfacial electron transfer process provides a means for the conversion of light directly into electrical power.

Excited state processes at sensitized nanocrystalline thin film semiconductor interfaces

Abstract The existing and potential technological importance of nanocrystalline semiconductor thin films sensitized to visible light by molecular chromophores have initiated considerable efforts toward understanding the detailed mechanisms of photoprocesses occurring at the interface. However, such studies are made difficult by the complex nature of kinetic processes observed following light excitation. In this paper, we review literature reports of excited-state processes in these materials and attempt to clarify the underlying mechanisms responsible for the complex kinetic behavior typically observed.

Nanostructured materials for environmental remediation of organic contaminants in water

Abstract Nanostructured materials have opened new avenues in various scientific fields and are providing novel opportunities in environmental science. The increased surface area-to-volume ratio of nanoparticles, quantum size effects, and the ability to tune surface properties through molecular modification make nanostructures ideal for many environmental remediation applications. We describe herein the fabrication of metal and semiconductor nanoparticles for environmental remediation applications, particularly in ground water. We then summarize literature reports of nanostructures specifically tailored for remediation of environmental contaminants including organohalides, trinitrotoluene, and phenols.