Co-deposition of Copper and Tin from Acidic Sulfate Solutions Containing Polyether Laprol 2402C: The Effect of Halides

Voltammetry and x-ray photoelectron spectroscopy data show micromolar amounts of halides to noticeably affect co-deposition of copper and tin from acidic sulfate solutions containing polyether Laprol 2402C as the surface-active substance. The reduction of Cu(II) slows down and that of Sn(II) accelerates in the series Cl^– < Br^– < I^–. Compounds on the surface of bronze coatings are oxides of Cu(I) and Sn(II) and halides of Cu(I).     

Partial processes during cobalt and molybdenum codeposition from solutions containing oxyacids

Distribution of citrate complexes of Co(II) and Mo(VI) in weakly acidic solutions is analyzed. It is found that the primary cathodic process is hydrogen evolution. When cathodic polarization is increased, Co(II) reduction is possible, while more negative potentials may result in full reduction of Mo(VI) to the metallic state. Reduction of H₃O⁺ ions in the solutions of oxyacids occurs with participation of a ligand playing the role of proton donor. Hydrogen evolution also remains the main electrochemical process in the molybdate solutions. It is assumed that Mo(VI) reduction occurs with participation of atomic hydrogen, but not all molybdate is reduced to metallic state. Co(II) reduction in solutions containing Mg(II) occurs to a higher extent but the degree of Mo(VI) reduction depends on the Co(II) concentration: increase in the latter results in a decrease in the content of metallic molybdenum in coatings.     

Dynamics of fluorescence depolarisation in star-shaped oligofluorene-truxene molecules

Star-shaped molecules are of growing interest as organic optoelectronic materials. Here a detailed study of their photophysics using fluorescence depolarisation is reported. Fluorescence depolarisation dynamics are studied in branched oligofluorene-truxene molecules with a truxene core and well-defined three-fold symmetry, and are compared with linear fluorene oligomers. An initial anisotropy value of 0.4 is observed which shows a two-exponential decay with time constants of 500 fs and 3-8 ps in addition to a long-lived component. The femtosecond component is attributed to exciton localisation on one branch of the molecule and its amplitude reduces when the excitation is tuned to the low energy tail of the absorption spectrum. The picosecond component shows a weak dependence on the excitation wavelength and is similar to the calculated rate of the resonant energy transfer of the localised exciton between the branches. These assignments are supported by density-functional theory calculations which show a disorder-induced splitting of the two degenerate excited states. Exciton localisation is much slower than previously reported in other branched molecules which suggests that efficient light-harvesting systems can be designed using oligofluorenes and truxenes as building blocks.     

Inhibition activity of ethyleneglycol and its oligomers on tin electrode

Voltammetry and electrochemical impedance spectroscopy were applied to investigate the inhibition activity of ethyleneglycol and its oligomers on tin electrode in strong acidic sulfate solutions. Tetraethyleneglycol was found to be the most active substance among compounds HO–(CH₂–CH₂–O) _m –H (m≤4) that retards diffusion-controlled Sn(II) reduction due to its inhibitive adsorption. This rather slow process is controlled both by diffusion and electrosorption steps. A comparison of exchange current densities obtained in the presence of different polyethers shows that the length of the hydrocarbon chain is the main factor responsible for inhibition activity of such substances on tin electrode.     

Simulation of electrochemical behavior of partially blocked electrodes under linear potential sweep conditions

The paper presents nonlinear model which stands for effective digital simulation of electrochemical behavior of partially blocked electrodes under linear potential sweep and cyclic voltammetry conditions. The model is based on a system of diffusion equations, also involving the Nernst diffusion layer. The mass transport is assumed to be regular in the entire diffusion space. The influence of the thickness of the resist layer on the behavior of the partially blocked electrodes is investigated. The agreement between the theoretical results and experimental ones is obtained to be admirable for several model electrodes with different blocking degree.     

Iridium metal complexes as an unambiguous probe of intramolecular vibrational redistribution

Ultrafast luminescence spectroscopy has been undertaken on three iridium cored phosphorescent complexes, with the Ir(ppy)3 molecule being compared with two Ir(ppy)3 cored dendrimers. Energy dissipation by intramolecular vibrational redistribution (IVR) and cooling shows as a luminescence decay because it decreases the admixture of singlet character to the emitting triplet state. A larger amount of vibrational energy dissipates by IVR in dendrimer complexes. We have therefore found a methodology of obtaining unambiguous information on the IVR process and show its potential to study IVR rates as a function of vibrational energy.     

Ultrafast luminescence in Ir(ppy)3

A femtosecond luminescence and transient absorption study of fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)₃] is reported. An emission with a lifetime component of 230 fs in the spectral region 500–560 nm is assigned to the population equilibration between electronic substates of the lowest excited triplet state, with energy dissipation by intramolecular vibrational redistribution. At shorter wavelengths a strong emission with a faster decay was observed and is attributed to a state with a higher admixture of singlet character. A slower decay on a 3 ps time scale is attributed to vibrational cooling. The results contribute to an understanding of the photophysics of transition metal complexes.     

Optical excitations in star-shaped fluorene molecules

A detailed study of the low-energy optical transitions in two families of star-shaped molecules is presented. Both families have 3-fold rotational symmetry with oligofluorene arms attached to a central core. In one family, the core of the molecule is a rigid meta-linked truxene, while the other is a meta-linked benzene moiety. The low-energy transitions were studied both experimentally and using time-dependent density functional theory (TD-DFT). The optical transitions of these new star-shaped molecules were compared with corresponding linear oligofluorenes. Both families of star-shaped molecules showed higher absorption and fluorescence dipoles and photoluminescence quantum yields than straight chain oligofluorenes. TD-DFT calculations show that absorption takes place across the entire molecule, and after excited state relaxation, the emission results from a single arm. In both theory and experiment the transition dipole moments show an approximate n(0.5) dependence on the number of fluorene units in each arm.