A blue chemiluminescence in the reaction of umbelliferone with hypochlorite

A strongly fluorescing 7-hydroxycoumarin (umbelliferone, U) oxidized in dilute (10 mumol/L-O, 1 mol/L) aqueous solution with CIO- or CIO- + H2O2 (but not with H2O2 alone) produces a strong chemiluminescence (CL). Light emission kinetics depends on the pH of solution (4.0-10.5) and the reaction has a low activation energy Ea = 31 +/- 2 kJ/mol (285-310 K). The spectrum covers the fluorescence of umbelliferone (400-550 nm, lambda max 460 nm). No red emission typical of 1 delta g, 1 sigma g, 1 sigma+g (O2)2 is observed either in the umbelliferone+CIO- or the umbelliferone +CIO- + H2O2 solution. The possible mechanism of CL and concomitant degradative oxidation of umbelliferone is discussed.