ELECTRONIC SPECTRA OF CHLOROPHYLLS 15 



cence (7). Tlie now confirmed presence of phospliorescence accounts, 

 in part, for the remaining energy and it may, in fact, account for all 

 of it in vivo. 



Certainly the advantageous properties of the triplet state com- 

 pared to the singlet state such as longer lifetime warrant serious con- 

 sideration and further investigations of the photosynthetic process 

 with the triplet state in mind. Moreover, the energy availability is con- 

 current with the seeming requirements for subsequent chemical re- 

 actions in photosynthesis as offered by recent authors. Practically all 

 work in the field of photosynthesis and photochemistry has been 

 concerned with the minor part of the energy and its possible mode of 

 utilization. It seems more reasonable to be concerned with the fate of 

 90% rather than with 10% or less of the available energy. 



Discussion 



Linschitz : The phosphorescence yield in vitro must be of the order of 70% or 

 so. Could I ask if you are going to account for the chemistry in vitro bj^ the triplet 

 state? Regardless of what happens in vivof In I'ivo do you think that the measure- 

 ment could possibly bring the jdeld up that high? 



Becker : I won't say yes and I won't say no. 



Rabinowitch : You mentioned that the photochemical energy yield in photo- 

 synthesis is up to 70%. That does not mean that the j'ield of phosphorescence is 

 70% in the absence of photos3'nthesis, because the metastable state can be de- 

 stroyed by internal conversion. 



Linschitz: That is true, but if you put in copper you can bring up the phos- 

 phorescence to ver}- high values. 



Becker: The chances are the jdeld is not low. I am not saying there is a 100% 

 quantum yield of phosphorescence. All I am saying is that the emission is 100% 

 phosphorescence. In other words, we obtained no fluorescence. 



Duysens: Is it possible that the quantum yield of phosphorescence is ver}- 

 small — say, 0.1 per cent? 



Becker: No, it wouldn't be that low. If I had to give an estimate, I would cer- 

 tainly say not less than .50% yield, on the basis of slit widths, exposure times, and 

 plate darkening. 



Duysens : There is no actual basis except it is a sort of culmination of times of 

 exposure, etc., giving some indication of intensity of emission. 



Jacobs: I would like to put in a plug for the importance of the h3'dration of 

 metal atoms for reactions in invo. A lot of work has been done on oxygen exchange 

 with water in the in vivo reactions of electron transport systems. It is one of the 

 first changes to disappear when the phosphorylation activity associated with 

 electron transport disappears. I think j'ou underestimate it. This hydration of 

 metal atoms may eventually (;au.se loss of a phenonienon which will turn out to be 

 important in photosynthesis as well as other processes associated with electron 

 transport. This is only a suggestion. 



