R. S. BECKER AND M. KASHA 41 



the possible low quantum yield of phosphorescence (not yet deter- 

 mined) of chlorophyll b would be similarly accounted for. 



In the living cell, it is possible that these dissipative effects, if ac- 

 tual, would be absent. This could be the secret of chlorophyll in the 

 living cell. Certainly, if electronic energy is dissipated as described 

 above, and if attachment of chlorophyll to some other molecule is 

 through the vinyl group in vivo, then most of the absorbed light 

 energy could become photochemically available. 



VII. Conclusion 



From our analysis of the spectroscopic interpretation of the chlo- 

 rophyll problem, it is apparent how little experimental investigation 

 has been made on the nature of the lower electronic states, which 

 would be involved in energy utilization processes. As a result, much 

 of our discussion has necessarily been speculative. However, we hope 

 that the viewpoint presented will stimulate further examination of 

 these points. In our developing research program we shall have the 

 opportunity to investigate experimentally many of the interpretations 

 made. 



Since our discussion is a preliminary one, we have refrained from 

 a discussion of the follow-steps in photosynthesis that have been 

 proposed recently. Once the primary step of energy utilization for 

 chemical reaction initiation has been established for the chlorophyll 

 system, the relation to the follow-steps should become apparent. Our 

 basic aim is to establish which electronic state of chlorophyll is in- 

 volved in this primary energy step, as contrasted with simple light 

 absorption. 



References 



Brealey, G. J., and M. Kasha. 1954. The role of hydrogen-bonding in the 

 n ^ TT blue-shift phenomenon. (Presented at the symposium on Molecular 

 Structure and Spectroscopy, Ohio State University, Columbus, June 14- 

 18). 



Calvin, M., and G. D. Dorough. 1947. The phosphorescence of chlorophyll 

 and some chlorin derivatives. Science, 105, 433-34. 



Calvin, M., and G. D. Dorough. 1948. The possibility of a triplet state inter- 



