Hydroxycoumarins as sensitizers and reactants of chemiluminescent oxidative reactions

Chemiluminescence (CL) of 7-hydroxycoumarin, umbelliferone, a strongly fluorescing compound, the precursor of photoactive furocoumarins widely spread in plant kingdom and used in dye lasers has been examined in four oxidative systems producing active oxygen species: A--horseradish peroxidase + H2O2 + buffers pH = 3-10; B--K3Fe (CN)6 + H2O2 + buffers pH = 4-12; C--NaOCl + buffer pH = 3-10.8; and D--HCHO + H2O2 + K2CO3 (Na2CO3), the so-called Trautz-Schorigin reaction. In all these systems a 10-1000-fold increase of CL intensity and quantum yield and an appearance of the blue emission band (lambda max = 460-480 nm), typical of the fluorescence of hydroxycoumarin used have been observed. Spectrophotometric and fluorimetric measurements of the systems A-D indicate that the tested hydroxycoumarins-coumarin, umbelliferone and 6-glucoside umbelliferone or esculin--undergo slow (systems A and B) and fast (systems C and D) consumption, leading to the degradation of coumarins. These findings suggest that efficiently fluorescing hydroxycoumarins may act both as sensitizers - secondary emitters of CL and/or reactants undergoing oxidative degradation.