Spontaneous Chemiluminescence During Oxidation of Cholesteryl Esters in Cholesteric and Isotropic Phases

Abstract

Chemiluminescence during free radical oxidation of cholesteryl esters has been studied in isotropic and cholesteric liquid crystalline phases. A dramatic enhancement of the chemiluminescent intensity was observed in the cholesteric phase. The emitter of chemiluminescence in this reaction is an electron excited ketone that forms during recombination of cholesteryl ester peroxyl radicals. It was shown that an enhancement of the intensity is due to an increase in both quantum yield of the excited state and emission yield of the emitter as the phase order increases. These phenomena are attributed to interplay between the orientational order of the medium and the anisometry of the reacting species. An increase in quantum yield of the excited state of the emitter is explained in terms of the increased rigidity of the transient tetraoxide complex during recombination of peroxyl radicals of cholesteryl esters in an anisotropic environment.