H. H. SEL/GER 201 



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o LUMINOL CHEMILUMINESCENCE 

 IN NaOH 



+ LUMINOL FLUORESCENCE (ACID) 



360 380 400 420 440 460 480 500 520 540 560 580 



m [X. 



Fig. 1. Chemiluminescence emission spectrum of luminol in 0.1 .\' \aOH initiated 

 with HoOo + NaOCl, and compared with fhiorescence of the neutral luminol mole- 

 cule in acid solution, pH 4. 



made that in alkaline solutions the chemical excitation of Itiminol 

 leaves it in the acid-stable form (3) . 



It is proposed that perhaps this picture is an unnecessarily com- 

 plicated one and that the emitting species in the luminol chemilumin- 

 escence is an excited state of the oxidized product, with a structure 

 not too different from the original luminol molecule. Since White 

 (7) has shown a concurrent evolution of No for linninol consumed 

 in the oxidation process, the assumption that light emission is due 

 to the neutral luminol molecule implies an energy transfer from the 

 excited oxidation product to a neutral luminol molecule. This 

 energy transfer fiuther implies a concentration dependence of the 

 chemilimiinescence quantum yield. This has been found not to be 

 the case. The relative chemiluminescence quantum yield for luminol 

 was measured over the concentration range from 10-" M to 10—^ M 

 in 0.1 N NaOH and w'as found to be constant, and independent of 

 concentration. A further arguinent against the supposition that the 

 linninol molecide is the emitting species, based on assumption II 

 above, is given by the data of Fig. 2 in which the experimentally deter- 

 mined fluorescence quanttmi yield of the luminol molecule is plotted 

 as a function of pH. At precisely those pH values where chemilumines- 

 cence occurs and is most efficient the fluorescence quantum yield of 

 the 430 ni/i, band decreases to zero. 



However, following the line of proposed intermediates suggested 



