16 K. S. BECKER 



Weigl : I would like to ii.sk if anyone has tried measuring pliosphorescence in- 

 tensity in vitro during a chlorophyll photosensitized reaction. It seems to me 

 that it is very important to demonstrate that it goes down very appreciably. 



Becker: I haven't and I don't know of anyone who has. 



Weigl : It seems to me that ought to be done. 



Livingston: I would like to make a slightly different interpretation of Dr. 

 Becker's own data. I think these data show that the yield of pliosphorescence, 

 meaning not the transfer to the triplet state but the actual yield of energy 

 as phosphorescence, must be less than 0.001. I am taking this in part from 

 a statement of Kasha's, that the observed intensitj^ of the phosphorescence was 

 less than the infrared contribution to the fluorescence. The infrared contribution 

 of fluorescence is certainly less than a few tenths of a per cent: so if that statement 

 is true, it would show that the phosphorescence has a yield of 0.001 or less. Also 

 you stated that the fluorescence in this infrared region obscured the phospho- 

 rescence; so that the fluorescence intensity must be much greater than the 

 phosphorescence, which again proves that the observable phosphorescence, the 

 omission of phosphorescent radiation, has a quantum yield less than 0.001; 

 nothing like 0.1. 



References 



1. Becker, R. S., and Kasha, M., "Luminescence spectroscopy of molecules and 



the ph«tosy nthetic sj'stem," pp. 25-45, in The Luminescence of Biological 

 Systems, F. Johnson, ed., American Association for Advancement of Science, 

 Washington, D. C, 1955. 



2. Becker, R. S., and Kasha, M., "Luminescence spectroscopy of porphyrin-like 



molecules including the chlorophylls," /. A7n. Chem. Soc, 77, 3369 (1955). 



3. Livingston, R., Watson, W., and McArdle, J., /. Arn. Chem. Soc, 71, 1542 



(1949). 



4. Calvin, M., and Dorough, G. D., "The possibility of a triplet state intermedi- 



ate in the photooxidation of a chlorin," J. Am. Chem. Soc, 70, 699 (1948). 



5. Freed, S., and Sancier, K., "Solvates of chlorophylls and related substances 



and their equilibria," J. Am. Chem. Soc, 76, 198 (1954). 



6. Evstigneev, V. B., Gavrilova, V., and Krasnovskii, A. A., Doklady Acad. 



NaukS.S.S.R. 70, 261 (1950). 



7. Forster, L., and Livingston, R., "The absolute quantum yields of chlorophyll 



solutions," J. Chem. Phys., SO, 1315 (1952). 



