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Quenching mechanisms of coumarin derivative 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) were carried out in different solvents using the steady-state method to understand the role of diffusion in the quenching mechanism. The solute was excited by UV radiation of wavelength 360 nm. Various quenching parameters like frequency of encounter, kd; probability of quenching per encounter, p; and quenching rate parameter, kq, were experimentally determined for all solvents. Activation energies of quenching, Ea, were also determined by using the literature values of activation energy of diffusion, Ed. It was found that the values of Ea were less than Ed in all solvents indicating that the quenching reactions are more significantly influenced by material diffusion.

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Quenching mechanisms of coumarin dyes, namely 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) and 8-methoxy-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (8MDTC), were carried out in toluene by adopting two methods, namely steady-state and time-resolved methods, to understand the role of diffusion in the quenching mechanism. The solute molecules were excited by UV radiation of wavelength 360 and 330 nm. Various quenching parameters like frequency of encounter (kd), probability of quenching per encounter (p and p′), and quenching rate parameter (kq and [Formula: see text]) were experimentally determined in all the solvents. Activation energy of quenching (Ea and [Formula: see text]) was also determined by using the literature values of activation energy of diffusion (Ed). It was found that the values of Ea (and [Formula: see text]) were less than Ed indicating that the quenching reactions are more significantly influenced by diffusion.

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This paper describes the combustion synthesis of a-Fe 2 O 3 nanopowder at much lower temperature and its catalytic activity for the one-pot preparation of 3,4-dihydropyrano[c]chromenes. The combustion derived a-Fe 2 O 3 nanopowder was characterized by powder X-ray diffraction (PXRD), Braunauer, Emmett and Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Highly efficient, three-component condensation of aromatic aldehyde, malanonitrile and 4-hydroxycoumarin catalyzed by a-Fe 2 O 3 nanoparticles at room temperature is described. The method offers an excellent alternative to the synthesis of 3,4-dihydropyrano[c]chromenes. The reactions are rapid, clean, and the products with good yield and high purity. #