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? NaOCI + 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 (λ_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 hydroxy-coumarins may act both as sensitizers – secondary emitters of CL and/or reactants undergoing oxidative degradation.