Spontaneous chemiluminescence during oxidation of cholesteryl esters in cholesteric and isotropic phases

Chemiluminescence during free radical oxidation of cholesteryl esters has b een studied in isotropic and cholesteric liquid crystalline phases. A drama tic enhancement of the chemiluminescent intensity was observed in the chole steric phase. The emitter of chemiluminescence in this reaction is an elect ron excited ketone that forms during recombination of cholesteryl eater per oxyl 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 o f the emitter as the phase order increases. These phenomena are attributed to interplay between the orientational order of thr medium and the anisomet ry of the reacting species. An increase in quantum yield of the excited sta te of the emitter is explained in terms of the increased rigidity of the tr ansient tetraoxide complex during recombination of peroxyl radicals of chol esteryl esters in an anisotropic environment.