198 LIGHT AND LIFE 



total reaction is exothermic with the release of 60 kilocalories. This will 

 be the energy available for the formation of the excited state. So the im- 

 portant point is we are breaking bonds which are strong. The only labile 

 bond which seems to be really useful in these circumstances seems to be the 

 oxygen-oxygen bond. I believe it is very interesting that all these reactions 

 involve peroxides, either hydrogen peroxide or the transitory formation of 

 another peroxide which, of course, all have this oxygen-oxygen bond. More- 

 over, if one produces a scheme of reactions in which an excited state is 

 created, it would appear to me logical that one should create this excited 

 state at the moment at which this bond disappears. 



Dr. Hastings: I would like to ask Dr. White if any of these non- 

 chemiluminescent, substituted derivatives are fluorescent? 



Dr. White: 7he answer is, in general, no. The chemiluminescence effi- 

 ciencies of the various phthalic hydrazides are roughly proportional to their 

 fluorescence efficiencies. This relation seems to hold for the phthalic acids 

 also. 



Dr. Hastings: If one could find one which was fluorescent but non- 

 chemiluminescent, and whose fluorescent emission spectrum differed from 

 the emission spectrum of the chemiluminescent compound, then one could 

 look for an energy transfer to the non-chemiluminescent molecule in the 

 reaction mixture. 



Dr. White: So far, we have assumed the simpler picture of chemilumines- 

 cence; namely, that an energy transfer is not involved and that one of the 

 reaction intermediates is the light emitter. 



Dr. Linschitz: We do find that at low temperatures (these things are 

 degassed in a vacuum line) some reversible changes take place which may 

 correspond to semiquinone fomiation. These changes are being looked into 

 in more detail, but for studying the chemiluminescent reaction we took 

 pains to avoid any possibility of having a photochemical reaction. 



I would like to ask Dr. White a question. Vou make a comparison of a 

 chemiluminescence spectrum at high pH and a fluorescence spectrum meas- 

 ured at a different pH. Now, if they do correspond, one may I think legiti- 

 mately argue tiiat the luminescence is coming from the same state, despite 

 the diff^erence in pH, since it is the acid strength of the excited state that 

 counts, riuis, it is possible that the same excited ionic form may be present 

 in both tile chemiluminescence and fluorescence experiment. In fact, the 

 spectroscopic data seem to me to be rather convincing on this point. 



Dr. White: This possibility has been eliminated (assuming that no special 

 interactions occur in the chemiluminescence) by the finding that basic 

 solutions of luminol do not fluoresce. It seems unlikely, therefore, that the 

 emission occurs from the singlet state of either luminol or the luminol anion. 



Dr. Strehler: Firstly, with respect to the eff^ect of light on porphyrin 

 catalyzed luminescence, the following may be of interest. A few years ago 

 we observed that chlorophyll in basic methanol in the presence of aldehyde 

 gives off a continuous luminescence for a number of hours. After this 



