Time-Resolved Fluorescence and Transient Spectroscopy in Determining Photochemical and Photophysical Channels in Reacting Systems in Solutions and Microheterogeneous Media

Abstract— Characterization of short-lived intermediates in homogeneous and microheterogeneous systems has been carried out using time-resolved spectroscopic techniques. The data obtained from these techniques have been analyzed in a relatively unconventional manner to elucidate complex transient behavior for two reactive systems. The highly nonexponential fluorescence decay for a series of fraws-stilbene-derivatized amphiphiles that readily form bilayer systems in aqueous media has been analyzed using a distribution of lifetimes analysis (DLA). The utility of DLA for quantitative studies was first determined by simulation of artificial decay data. Despite some limitations in DLA, qualitative conclusions as to the nature of the fluorescing species may be drawn when supplementary information such as steady-state spectroscopic data are also considered. The results indicate that the observed fluorescence originates from different types of excited-state species that consist of two or more trans-stilbene units; one of the emissions is attributed to the excited state of a ground-state aggregate while the other is assigned to an excimer that may arise from a 'defect'in the bilayer. The nonexponential nature of the decays is attributed to distributions of environments experienced by the fluorescing species. Electron transfer (ET) reactions between several excited pinacols and carbon tetrachloride in solution have been found to yield products with quantum yields that are higher than unity in the presence of oxygen, suggesting a chain mechanism for product formation. In these systems both the donor and the acceptor undergo bond fragmentation following the initial ET step. The individual steps involved in the proposed mechanism for these systems have been investigated in part using different steady-state and time-resolved laser spectroscopic techniques. However, it was also necessary to utilize pulse radiolysis in order to confirm the involvement of certain radical intermediates that were not observable by the usual flash photolysis techniques.     

Copper(I) 3-Methylsalicylate Mediates the Chan–Lam N-Arylation of Heterocycles

Copper(I) 3-methylsalicylate (CuMeSal) mediates N-arylation reactions between aryl boronic acids and aromatic heterocycles (Chan–Lam coupling) under moderate reaction conditions (K₂CO₃, methanol, 65 °C, in air, 3–5 h). Both electron-rich and electron-deficient aryl boronic acids and a diverse set of N-heterocycles were allowed to react and gave N-arylation products in reasonable yields, which demonstrate the utility of this catalyst.     

Synthesis and antibacterial activities of novel 2,5-diphenylindolo[2,3-e] pyrazolo[1',5':3",4"]pyrimido[2",1"-c] [1,2,4]triazines

The formation of (E)-3-{2-(2,5-diphenylpyrazolo[1,5-c]pyrimidin-7-yl)hydrazono}indolin-2-ones 3 has been achieved by condensation of equimolar amounts of 7-hydrazino-2,5-diphenylpyrazolo[1,5-c]pyrimidine (1) and isatin (or isatin derivatives) 2 at room temperature. The (E)-products could be isomerized into corresponding the (Z)-3 isomers. Reactions of the latter fused heterocyclic hydrazones towards different electro-philic reagents yielded the corresponding 3-substituted derivatives 4-7. Dehydrative cyclisation of the hydrazones 3 using phosphorus oxychloride afforded the 2,5-diphenyl- indolo[2,3-e]pyrazolo[1',5':3",4"]pyrimido[2",1"-c][1,2,4] triazines 13. The polyfused heterocyclic ring system 13 underwent electrophilic substitution reactions at position 4 rather than at position 3. The 3-bromo isomer of 17 was prepared by a sequence of reactions starting from 2,5-diphenylpyrazolo[1,5-c]pyrimidine-7(6H)-thione (11). The orientation of the electrophilic attack was supported by spectroscopic and chemical evidence. Some of the synthesized compounds were found to possess slight to moderate activity against the microorganisms Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa.     

Profit loss in differentiated oligopolies

We provide sharp lower and upper bounds on the ratio of decentralized to centralized profits when multiproduct firms offering differentiated products engage in price competition. The bounds depend on the demand sensitivity matrix but are independent of marginal costs.     

Tandem arylation-reduction of acyl heterocycles. Convenient synthesis of benzyl heterocycles

Tandem arylation-reduction of a series of acyl heterocycles using phenyl-, 4-methylphenyl-, and 4-methoxy-phenyllithium reagents followed by lithium-ammonia-ammonium chloride reduction afforded the corresponding benzyl heterocycles. The acyl heterocycles surveyed in this study contained furan, 2,3-dihydro-4H-1-benzopyran, 4H-1-benzopyran, thiophene, 4,5,6,7-tetrahydrobenzo[b]thiophene, 2,3-dihydro-4H-1-benzothiopyran, and pyridine nuclei. All acyl heterocycles yielded the corresponding benzyl heterocycles except 2,3-dihydro-4H-1-benzothiopyran-4-one, which selectively cleaved during reduction to give the corresponding 2-(1-arylpropyl)benzenethiols.