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Despite its high refractive index sensitivity, localized surface plasmon resonance (LSPR) spectroscopy has been generally restricted to large biological analytes. Sensing of smaller molecules is a compelling target for this technique; in particular, LSPR spectroscopy could be utilized to detect hazardous or toxic gases and manage industrial processes involving gaseous chemicals. Here, we report sensing of pure gases over Ag nanoparticles using LSPR spectroscopy, where the detected changes in bulk refractive index are 10.1021/ac102127p

Differences in the relative energies of the interconfigurational (IC) transitions for the fully oxidized (+6) states of the osmium systems demonstrate that stereochemical effects lead to fundamental changes in the energy levels of the metal-based dpi orbitals, which are split by spin-orbit coupling and ligand-field asymmetry. An increase in the separation between the IC bands as BL is varied reflects the increase in the degree of electronic coupling through the series of ruthenium and osmium complexes.

A series of C- and Z-shaped complexes of the form cis- and trans-[Re(CO)3(L)2BiBzlm, where L = 4-phenylpyridine, 2,4'-bipyridine, or pyridine and BiBzlm = 2,2'-bisbenzimidizolate, are synthesized. The compounds are acyclic analogues of studied tetraehenium molecular rectangles and are of interest, in part, due to their potential to form ligand-centered mixed-valence compounds upon reduction by one electron.

A series of six neutral, tetrametallic, molecular rectangles are synthesized that have the form ([Re(CO)3]2BiBzlm)2-Mu,Mu'-(LL)2, where BiBzlm is 2,2'-bisbenzimidazolate and LL is reducible, dipyridyl or diazine ligand. The X-ray crystallography and computational modeling shows that the observed differences largely reflect detailed geometric configurational differences that can either facilitate or frustrate productive direct orbital overlap.

A real-time deoxyribonucleic acid (DNA) detection method that uses single-strand DNA (ssDNA)-modified nanoparticle probes and micropatterned chemoresponsive diffraction gratings interrogated simultaneously at multiple laser wavelengths is presented. Significant signal amplification is observed due to the use of nanoparticle probe, which is heavily functionalized with ssDNA complementary to target DNA.

Micropatterned polymeric diffraction gratings have been fabricated and evaluated as volatile organic chemical sensors. When operated under nonresonant conditions, sensor elements were found to respond in a rapid (response time 5-15 s) and reproducible fashion to each analyte investigated. Relative response magnitudes were found to be in qualitative agreement with those obtained via surface acoustic wave techniques. Preliminary limits of detection as determined by investigations with micropatterned polyepichlorohydrin, polyisobutytene, and polybutadiene gratings, respectively, were found to be 8, 11, and 7 ppm for toluene, 25, 258; and 72 ppm for methyl ethyl ketone; 41, 102, and 34 ppm for chloroform; and 460, 60, and 59 ppm for hexane. While generally less than 1 order of magnitude higher than those observed for identical polymer/analyte combinations in SAW studies, the observed limits of detection were at or below governmental standards (OSHA-PEL and NIOSH-REL) for each analyte evaluated. These diffraction-based sensors show promise for integration into an array-based sensor system, providing simultaneous identification and quantification of unknown analytes and simple analyte mixtures.

Micropatterning of the vaporchromic charge-transfer salt, [Pt-(CNC6H4C10H21)(sub 4)][Pd(CN)(sub 4)], on transparent platforms yields such structures that behave as transmissive chemoresponsive two-dimensional visible-region diffraction grating or photonic lattices. These lattices are investigated as volatile organic compound (VOC) sensors via a newly devised signal transduction scheme involving diffraction of visible light.

Research has been conducted on the charge transfer within different (X (sub)2 -bipyridine)Re (super)I (CO) (sub)3 Cl complexes. The use of the transient DC photoconductivity, Stark emission spectroscopy and ground-state dipole moment measurements in examining this charge transfer is discussed.

A computational approach for estimating thermal electron-transfer reaction distances in symmetrical mixed-valence compounds is presented. It is concluded that electronic delocalization effects can prompt effective one-electron-transfer distances to differ from simple geometric separation distances.

This paper describes a new approach for quantification of rates of molecular transport through patterned, or otherwise heterogeneous, porous films supported on conductive substrates. Scanning Electrochemical Microscopy (SECM) has been used to image molecular sieving of redox active probes by thin, electropolymerized films of Fe(5-amino-1,10-phenanthroline)(sub 3)(super 2+) on micropatterned and microdisk array electrodes. Films as thin as 12 nm completely block redox mediators with average molecular diameters greater than 12 angstroms, whereas smaller diameter probes (radii 5-8 angstroms) were observed to permeate selectively. SECM tip currents measured for three different redox permeants/mediators are observed to decrease with increasing polymer thickness, consistent with a transport model that includes partitioning into and diffusion within the polymer films. Permeabilities, PD(sub f), within the poly[Fe(5-NH(sub 2)-phen)(sub 3)(super 2+) films have been quantitatively determined from the SECM tip currents and are in excellent agreement with data previously obtained from rotating-disk electrochemistry. This new methodology provides a versatile approach for quantitative investigation of membrane transport and permeation selectivity with good lateral spatial resolution.

A putative octupolar super chromophore Ru(trans-4,4'-diethylaminostyryl-2,2'-bipyridine)(sub 3)(super 2+) has been analyzed using the polarized hyper-Rayleigh scattering technique. It was found that the symmetry of the excited state, and therefore the hyperpolarizability tensor, is dipolar in nature, as shown by electroabsorption or electronic Stark effect experiments. These results indicate that changes in dipole moment correlate with optical excitation.

Thin-film forms of molecular materials composed of selected tetrarhenium square assemblies were prepared and identified. It was believed that the films were intensely attached and characterized by few pinhole defects. Results of the electrochemical transport experiments revealed that the materials were porous in terms of small solution-phase permeants although hindering larger permeants. Also, a single isomer crystal structure was discovered in one of the square assemblies.

Electroabsorption and related spectroscopic studies were conducted on bimetallic tetraiminoethylenedimacrocyclic complexes. Additional near-infrared Raman investigations on mixed valent and isovalent diiron species support the observed delocalized mixed-valence ion behavior. Results also show that electroabsorption causes anomalous polarizability and that metal-to-ligand charge transfer excitation causes the blue green electronic absorption band in the mixed-valent complex.

Sol-gel-encapsulation technology of fragile molecules and biomolecules such as enzymes/coenzymes in clear, porous silicate matrices has been successfully demonstrated. The inherent alcohol-plus-aldehyde dual response capacity of the silicate-encapsulated yeast alcohol dehydrogenase enzyme/cofactor combination to transform irreversible probes into reusable chemical sensors is investigated. The results are discussed.

The intrinsic charge localization in the formed state of metal-to-ligand charge transfer (MLCT) excited-state formation was established through utilization of Electronic Starck effect measurements. Data indicated that the transition involved the production of a charge-localized state. It was further indicated that the 'singlet' MLCT excited state of Ru(phenanthroline)3(super)2+ resembled the MLCT state of the bipyridine analogue.

Research into electron transfer kinetics and interfacial energetics is expanding the knowledge of the physical chemical basis for efficient sensitization of metal-oxide semiconductors used in solar cells. The semiconductor/liquid junction in the solar cell is responsible for the solar energy conversion through the movement of particles between the semiconductor and the solution through the semiconductor/solution interface. Every oxidation reaction is offset by a reduction reaction, increasing efficiency.

The spin-orbit induced splitting of the visible-region intervalence transition was observed to study the orbital specificity of the charge transfer process. Raman and electronic effect spectroscopies were used investigate the resonance of the component transitions. Measured orbital-specific electron-transfer distances, coupling energies and reorganization energy were shown to be dependent on orbital identity.

The charge transfer of pyridinium ions that are directly attached to Ru(bpy)sub3super2+ is not observed in the photoexcited state of the donor. The tris(bipyridyl)ruthenium dication has a 4,4'-bipyridinium ion that is attached by nitrogen-carbon bond at the four site of the single 2,2'-bpy ligand. The 2,2'-bipyridine has an interplanar angle of 28 degrees between two 4,4'-bpy rings. The two 4,4'bpy rings have an interplanar angle of 24 degrees. The four ruthenium polypyridyl complexes exhibit metal-to-ligand charge-transfer transitions that are similar to ruthenium(II) bypiridine.

A tricarbonylrhenium (bi)pyridine based donor/crown/acceptor assembly undergoes photoredox reactivity consisting of rhenium-to-pyridine charge-transfer absorption before electron transfer to Re(II) from the pyridine anion reduced nitrobenzene. Quenching and nuclear magnetic resonance spectroscopy at different temperatures reveal that the folding kinetics is accelerated at low temperature, low dielectric strength solvents, and in metal-to-ligand charge transfer excited state than the ground state.

The aqueous (D2O) self-exchange kinetics studies for (trimethylammonio methyl)ferrocenium/ferrocene (TMAFc2+/+) as a function of beta-cyclodextrin encapsulated are described. The results showed that the electron self-exchange rate constant for TMAFc2+/+ in D20 decreased by a ca. 20-50 fold in the presence of beta-cyclodextrin. The decrease has been attributed to the increase in thermal activation barrier, reflecting the incipient need to transfer the cyclodextrin host.

The reaction of trans-dioxorhenium complex with methyl trifluoromethanesulfonate produces high-valent, highly stable oxo-, methoxorhenium complexes. These complexes are identical to analogous oxo, hydroxo complexes of trans-dioxorhenium(V)tetrapyridyl species, which is a model system for interfacial two-electron, two proton transfer reaction sequences. High pH stabilizes the rhenium(IV) state for several complexes with respect to redox disproportionation.

Intervalence absorption spectroscopic studies show that an inert electrolyte exhibits significant influence on the energetics of optical electron transfer (ET) in (NC)5Fe(III)-bis(pyridyl)ethylene-Fe(II)(CN)(sub 5)(super 5-). A model incorporating energetic consequences of stepwise ion pairing explains the above compound in different ionic strength solutions of LaCl3, CaCl2 and NaCl. This model explains the optical intervalence properties of (NH3)5Ru(III)-4, 4'-bpy-Ru(II)(NH3)(sub 5)(super 5+) in aqueous Na2SO4 solution. Ion-pairing-stimulated symmetry reduction and subsequent restoration influence optical electron transfer.

A three-site description of electronic delocalization helps explain quantitatively the intervalence energy effects associated with double crown encapsulation of the Creutz-Taube ion. Increase in the size of the macrocycle increases the energy shifts in both the near-infrared and visible portions of the electronic absorption spectrum. Improved parameterization of the model enhances the agreement between the expected and observed crown effect on MLCT and intervalence energies.

The effects of host (crown ether) size and structure and guest (ruthenium complex) oxidation state and primary ligand environment on binding strength were reported. It was found that binding increases with increased size and flexibility of the crown ether. It also increases with increased availability of ammine ligands, higher oxidation state and increased Lewis acidity of the guest. Small amounts of crown ether can also have substantial effects upon metal-ligand and metal-metal charge-transfer interactions.

The environmental effect of intervalence transition for trans-(py)(NH3)4Ru-pz-Ru(NH3)4(py)5+, a structure comparable to the Creutz-Taube ion, is analyzed according to its response to both solvent and added electrolyte. Using dimethyl sulfoxide as the electrolyte and acetonitrile as solvent, intervalence effects are observed through the absorbance differences obtained.

The electrochemical examination and oscillator strength measurements of Ru(NH3)4(2, 2'-bipyridine)2+ and Ru(NH3)4(1,10-phenanthroline)2+ metal/ligand orbital mixing show differing experimental results. The electrochemical method detects a considerable degree of electronic delocalization while the spectral measurement detects less than two percent delocalization. However, a separate spectroscopic counter-study favors the results obtained from the electrochemical technique. This study shows that the electrochemical study of the two Ru compounds provides an accurate representation of metal/ligand orbital mixing and partial charge-transfer reactions.

A family of anisotropic open-framework compounds is obtained based upon paddle-wheel-type coordination of Zn(II) pairs in two dimensions and pyridyl ligand pillaring in the third. The mixed-ligand approach is used to tune channel dimensions, to introduce otherwise unstable metal/pyridine linkages, and to engender framework redox reactivity.

gA pulse-field gradient nuclear magnetic resonance spectroscopic technique for determining the size of a tetrametallic molecular square is described. The method utilizes molecule's self-diffusion coefficients relative to those from other isostructural compounds with an inverse relationship with hydrodynamic radii, which roughly represents the cube of the assembly's mass.

Research has been conducted on the rhenium-linked porphyrin dimers. The synthesis, photophysical characterization and preliminary energy transfer applications of these dimers based on the rhenium pyridyl ligation are discussed.

Research demonstrates measuring charge-transfer characteristics of the emission properties of the excited states of bipyridine complexes using transient direct current photoconductivity technique.

Research demonstrates the application of transient direct current photoconductivity technique to inorganic systems in the investigation of charge-transfer reactions in solutions of pt(dpphen)(ecda) at room temperature. Result indicate that the technique can be extended to other related compounds to study relationship between one-electron-transfer distances and molecular structure.

Trimethylaminomethyl(ferrocenium/ferrocene) (TMAFc super 2+/+) self-exchange studies in water with the negatively charged molecular host calix 6 arene-p-sulfonate generated two contributing factors. The extent of oxidation-state dependence of the guest/host association constant was smaller for 1(super n-)TMAFc(super 2+/+) than for beta-cyclodextrin/TMAFC(super 2+/+) or the ammine ruthenium/crown ether systems. Another factor was the opposite charges of the free guests and the guest/host assembly which triggered the net acceleration of the exchange kinetics.

Fabrication of a ZIF-8 thin film-based Fabry-Perot device as a selective sensor for chemical vapors and gases is reported. The newly prepared ZIF-8 thin film and a series of ZIF-8 thin films of various thicknesses grown on silicon substrates are also reported.

Nickel bis(dicarbollide) is used as a fast, one-electron outer sphere redox couple in dye-sensitized solar cells and device performances with this anionic shuttle are examined. Open-circuit voltage decay is used for probing the kinetics of the Ni(III)/(IV) bis(dicarbollide) redox couple and electron interception is slower than ferrocene/ferrocenium, which has described the large discrepancy in open-circuit voltage potentials between these two redox shuttles.

The article presents a new approach, which employs the process of rational designing of the various organic building blocks for controlling the catenation of the metal-organic frameworks (MOFs). The synthesis and the applications of these MOFs are also discussed.

The excitation-wavelength-dependent Raman spectra of the species trans-(O)2Re(py-x)4(super 1+), where py-x = pyridine or pyridine derivative, was studied. The trans-dioxo complexes exhibited absorption regions at ca. 440 nm and ca. 350 nm. The ligand-field transition also featured peaks at 822 cm(super -1) and 907 cm(super -1) which were assigned to the asymmetric oxygen-metal and the O-double bond-Re-double bond-O modes, respectively. The near-UV absorption in the charge-transfer region was assigned as rhenium-to-pyridine charge transfer.

The mechanisms involved in the electrochemical reduction of cis- and trans-dioxorhenium(V) species in acidic and neutral solutions is reported and quantitative measurements of the accompanying electrochemical kinetics is made. Results indicate that access to Re(IV) is a significant factor in the differentiation of cis/trans electrochemical kinetics. Moreover, comparisons to isoelectronic osmium species makes possible a semiquantitative reactivity analysis.

The mixed-valence compound (NH3 5 Ru-NC-Fe CN 5)Na was synthesized and its intervalence thermochromism was investigated. A transient thermochromic bleaching and recovery was expected in view of the intervalence absorbance measurements made on the high-energy side of the intervalence band and the negative sign of dE(sub op)/dT. It follows that a sign reversal should result fron measurements on the low energy side. These indicate that the driving force is temperature-dependent and that it is most negative when the temperature is at its lowest.

Eleven linked donor- (chromophore-) acceptor complexes have been synthesized. The complexes consist of the Re(CO)3(ligand) unit as the chromophoric donor, the encapsulation unit linked directly to 2,2'-bipyridine or pyridine and an electron acceptor, another chromophore or a redox-inactive site. The excited-state lifetimes of the complexes revealed that a rhenium-to-pyridine-based charge-transfer state existed with an energetic ordering of py > bpy > py-crown (or py-ester) > bpy-crown (or bpy-ester).

The bridge-mediated charge-transfer kinetics of L(NH3)4Ru(super III)N-triple bond-CFe(super II)(CN 5)1- were studied. Differential-pulse voltammetry indicated positive shifts in E(sub f)(Ru) as NH3 is displaced progressively by 4-methylpyridine and the other electron-withdrawing ligands. Potential shifts of the indirectly disturbed redox site was also revealed. Differences in the estimates of orbital mixing for the species are accounted for by the geometric distance between donor and acceptor metal ions which can exceed the true charge-transfer distance.

The application of redox quenching processes after photochemical excitation is a new method for the assembly of metallopolymeric films. The visible-region photolysis of an acetonitrile solution of Ru(vbpy)2(super 2+) and BPh3R(super 1-) between conductive glass and ordinary glass plates generates a polymeric coating on the plate nearest to the light source. Films are obtained easily from solutions containing triphenyl-n-hexylborate but not from those containing tetraphenylborate. Electrochemical determination indicates that thinner films are more electroactive than the thicker ones.

Click chemistry is used for constructing a postsynhetically modified noncatenated, Zn-based metal-organic framework (MOF) material bearing silyl-protected acetylenes. A solvent-based, selective deprotection strategy is used for clicking two different organic azides onto the MOF crystals, which have resulted in a porous material whose internal and external surfaces are differently functionalized.

Titanium dioxide based dye-sensitized solar cells are prepared that have incorporated corrosion-protected silver nanoparticles as plasmonic optical elements of the photoelectrode. The optical enhancements have translated into photocurrent enhancements, with the thinnest Ti[O.sub.2] coatings showing 9-fold current enhancements under optimal monochromatic illumination.

The tetratopic ligand 1,2,4,5-tetrakis(4-carboxyphenyl)benzene is used as a key building block for preparing a permanently microporous metal-organic framework with Lewis acidic (porphyrin)Zn struts (ZnPO-MOF). ZnPO-MOF has efficiently catalyzed acyl-transfer reactions by preconcentrating the substrates within its pores.