BENTLEY GLASS 845 



It" eledion tiansler is imolvcd. as seems probable, a chargc-transler 

 complex ol metal ami hydioxyl ion may be produced, in which case 

 the excitation may arise irom removal of the OH and the dropping 

 back of the electron into an excited orbital instead of the ground 

 state. Or one may devise chain reactions that have the same result. 



Linschitz states that recent experiments in his laboratory on the 

 quenching of excited triplet states in aromatic molecules, including 

 porphyrins, by heavy metal ions provide further evidence of charge- 

 transfer intermediates. Ionic intermediates may thus play an im- 

 portant role in promoting electronic transitions, though atom transfer 

 may also serve in the formation of intermediates in chemiluminescent 

 reactions. 



The brilliant chemiluminescence of luminol (Fig. 3) is unsurpassed 

 among the hydrazides. Emil White points out that maleic hydrazide 

 and linear, rather than ring, hydrazides are but weakly luminescent. 



rig. 3. Structural formula of luminol. 



Studies of analogues of luminol reveal that in general a diacyl- 

 hydrazine heterocyclic ring bearing two hydrogen atoms is necessary 

 and for efficient chemiluminescence it should be attached to an aro- 

 matic ring. Substitutions at position 5 are superior to those at posi- 

 tion 6, and the efficiency of the substituent is related to its ability to 

 release electrons into the conjugated system. It is the resonance 

 effect that is involved. A similar effect of the substituent side-groups 

 occius in the fluorescence of these compounds and of the correspond- 

 ing phthalic acids, so that their effect would seem to be exerted 

 at the time of emission of the light. In water, the chemiluminescent 

 system must include sodium or potassium hydroxide, hydrogen per- 

 oxide, and an oxidizing agent such as sodium hypochlorite, potassium 

 ferricyanide, or a chelated transition metal, such as an iron or copper 

 complex. No product of the oxidation reaction has been identified 

 except nitrogen; but since the quantum yield is not above 0.003 this 

 is not surprising. Lmninol is not a catalyst in the reaction but is 



