Non-quadratic-intensity dependence of two-photon absorption induced fluorescence of organic chromophores in solution

We have provided a model to interpret the non-quadratic-intensity dependence behavior commonly observed in the two-photon fluorescence (TPF) experiment excited with high laser intensity. The model also provides one with a different technique to measure the two-photon absorption cross section of an organic chromophore in solution. In contrast to the commonly used low intensity technique that depends on the quadratic-intensity law, the present technique is based on the non-quadratic-intensity dependence of two-photon fluorescence. Auxiliary data such as two-photon quantum efficiency and fluorescence collection efficiency, essential in the low intensity method, are not required in the present technique. TPF measurements of Rhodamine B in methanol are carried out to demonstrate the validity of the present method. The method is used to determine the two-photon absorption cross section of a new chromophore attached with tricyano-derivatized furan as the electron acceptor. The two-photon absorption cross section measured using this method is also compared with that using a conventional transmission technique.     

The electrooxidation of methanol and related compounds at ruthenium dioxide-coated electrodes

The underlying metal was observed to corrode when a ruthenium dioxide-coated titanium electrode was anodized in an aqueous methanol solution. With a similarly coated platinum electrode peaks were observed on the voltammogram below 1.0 V which were attributed to methanol oxidation on the underlying metal. This effect was more pronounced when the electrode was subjected during cycling to potentials close to 0 V. Rapid oxidation of methanol on RuO₂ was observed at potentials above 1.0 V, the rate at a given potential increasing in an approximately linear manner with increasing alcohol concentration. The rate of reaction also increased with increasing temperature and increasing surface roughness. Tafel slope values were rather high (>100 mV decade^?1) and a mechanism involving anodically generated species such as OH_ads was proposed to account for these results. The variation of activity with pH was similar to that reported earlier for oxygen evolution at these anodes and this was again explained in terms of partial deactivation of the surface due to a combination of proton loss and phosphate ion adsorption at intermediate pH values. The release of carbon dioxide from aqueous solutions of higher alcohols at 25°C confirmed the high oxidizing power of RuO₂ anodes.     

Uranyl coordination environment in hydrophobic ionic liquids: an in situ investigation

Different inner-sphere coordination environments are observed for the uranyl nitrate complexes formed with octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide and tributyl phosphate in dodecane and in the hydrophobic ionic liquids (ILs) [C(4)mim][PF(6)] and [C(8)mim][N(SO(2)CF(3))(2)]. Qualitative differences in the coordination environment of the extracted uranyl species are implied by changes in peak intensity patterns and locations for uranyl UV-visible spectral bands when the solvent is changed. EXAFS data for uranyl complexes in dodecane solutions is consistent with hexagonal bipyramidal coordination and the existence of UO(2)(NO(3))(2)(CMPO)(2). In contrast, the complexes formed when uranyl is transferred from aqueous nitric acid solutions into the ILs exhibit an average equatorial coordination number of approximately 4.5. Liquid/liquid extraction results for uranyl in both ILs indicate a net stoichiometry of UO(2)(NO(3))(CMPO)(+). The concentration of the IL cation in the aqueous phase increases in proportion to the amount of UO(2)(NO(3))(CMPO)(+) in the IL phase, supporting a predominantly cation exchange mechanism for partitioning in the IL systems.     

Effect of catalysts on the reaction of an aliphatic isocyanate and water

The kinetics of the reaction of aliphatic isocyanate with water were investigated with hexyl isocyanate as a model compound. The kinetic study was carried out with a titration method to determine the concentration of the isocyanate group as a function of time. Gas chromatography was used to augment the kinetic data obtained from the titration method. The effects of an organic acid [p‐toluene sulfonic acid monohydrate (p‐TSA)], a tertiary amine {diazabicyclo[2.2.2]octane (DABCO)}, and an organotin compound [dibutyltin dilaurate (DBTDL)] on the reaction were investigated for the conversion of isocyanate to a urea. Under the reaction conditions in this study, urea was the only product observed. The rate constants indicated that p‐TSA had low catalytic activity, DABCO had intermediate catalytic activity, and DBTDL had high catalytic activity. A reaction mechanism was proposed for each of the catalysts. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1677–1688, 2002