MICHAEL KASHA 63 



planation as Piatt did, but were of the opinion that the long-wave- 

 length shoulder \\as of n -^ tt* type, since the spectral shift re- 

 quired is well within the range of other n -^ 77* blue shifts. Fernandez 

 and Becker (7a) have made further quantitative measurements on 

 cholorphyll-a and chlorophyll-b, confirming the earlier results, and 

 extending the observations to low temperature emission spectroscopy. 

 Becker's observations (7a) confirm the ideas of Franck (8) con- 

 cerning the importance of lowest 71,77* excited states in photosynthesis. 

 In particular, they reinforced the possibility that two kinds of chloro- 

 phyll, wet chlorophyll in an aqueous phase, and dry chlorophyll, in 

 a lipid phase, may each carry out complementary functions in the 

 photosynthetic system. 



The importance of ;? -^ tt* transitions in heteroaromatic systems 

 should be evident, both from the point of view of their wide occur- 

 rence, as well as from the point of view of their characteristic features. 

 New biological applications will doubtless be revealed. At the same 

 time, further fundamental researches on the nature of the w —> tt* 

 transition are required before the principal features of this process 

 can be thorousjhlv understood. 



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1. Badger, G. M., and ^Valkel•, I. S., /. Chem. Soc, 122 (19r)6). 



2. Becker, R. S., and Kasha, M., in Luminescence in Biological Systems (F. H. 



Johnson, ed.), p. 25, American Association for the Advancement of Science, 

 \Vashington. D. C. (1955). 



3. Brealev, G. J., and Kasha, M., /. Am. Chem. Soc, 77, 4462 (1955). 



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9. Fresco, J. R., and Gorn. R., unpiib. 



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