No abstract

Kinetics of acidic Mn(VII) oxidation of acetaldehyde in aqueous and 5% ethanol-water solvents were studied via pseudo-first order condition at λmax 525nm. The reaction showed a first order dependence with respect to acetaldehyde concentration, [Mn(VII)], fractional order to [H+] and independent on the ionic strength of the solution. Michaelis-Menten plot showed the existence of an intermediate complex and dependence on hydrogen ion is in the form kobs= a + b[H+]. However, oxidation reaction is generally faster in non-aqueous solvent than in aqueous solvent. Product analysis revealed the presence of carboxylic acid and stoichiometric study suggests the consumption of 2 moles of MnO4-by 3 moles of acetaldehyde in both solvents. Thermodynamic parameters of activation were obtained from Arrhenius and Erying's equations. A plausible associative mechanism in agreement with kinetic and spectroscopic results was proposed.

This study reported a theoretical design of four sets of new organic D−π−A sensitizers consisting of three dyes in each set (D1A1‒D4A3) in incorporating Silole and thieno[3,4-b]pyrazine derivstives using DFT and DT-DFT methods. The molecular properties such as, geometries, the frontier molecular orbitals, the energy gaps, reactivity indices, electron accepting power and electron donating power were calculated. The results showed that boron-containing dyes (D1A3, D2A3, D3A3 and D3A3) have shorter C2-C3 bond length, lower energy band gap (∆Eg) and longer absorption wavelengths (λmax) (ordered as S > Se > BH2), which lead to profound effect on the electronic properties for the dyes. The chemical potential (µ), glogal eletrophilicity index (ω) and electron accepting power (ω+) revealed that B-containing dyes are more electrophilic in characters than other dyes in each series; thus electron are withdrawn or depleted from the donor subunit of the dyes by BH2 insertion to thieno[3,4-b]pyrazine subunit. The results of open circuit voltage (Voc), light harvesting efficiency (LHE) and light electron injection driving force (ΔGinject) calculated for the dyes showed that they have good photoelectric conversion efficiency but with low dye regeneration (ΔGregen) ability. Also, high excited state lifetime (τesl) values of B-containing dyes (D2A3, D3A3 and D4A3) would lead to more stability of the dyes in the cationic state for a longer time, which may result in higher charge transfer efficiency; thus enhancing electron injection efficiency of the dye-sensitizers for dye-sensitized solar cell (DSSC).