Luminescence Spectroscopy of Molecules 

 and the Photosynthetic System* 



R. S. Becker and M. Kasha 



Department of Chemistn', Florida State University, 



Tallahassee, Florida 



I. Scope of Present Discussion 



In recent years numerous advances in the interpretation of electronic 

 states and transitions in complicated molecules have been made. We 

 shall discuss the application of those results which we believe to be 

 of importance for the chlorophylls in their role of energy transfer 

 agents in photosynthesis. Our discussion will be qualitative and with- 

 out the complications of spectroscopic nomenclature and symbolism. 

 Moreover, we shall omit all discussion of such fine points concerned 

 in the electronic transitions as symmetries, polarizations, vibrational 

 fine structure, and assignments. We believe that these points, however 

 intrinsically interesting they may be to the professional spectroscopist, 

 will not be involved directly in the problem of photosynthesis. 



On the other hand, we shall discuss all those spectroscopic aspects 

 which we believe will be important in the capabilities for utilization 

 and transfer of electronic excitation energy by the chlorophylls. As 

 will be shown, this discussion will be limited perforce to the lowest 

 electronic states of the molecules, namely, the ground (singlet) elec- 

 tronic state, the lowest triplet excited state, and the singlet excited 

 states (our discussion requires the plural) involved in the red ab- 

 sorption band of the chlorophylls. Specifically, the Soret band and 

 higher energy transitions we shall disregard, in accordance with the 

 role of Internal Conversion discussed in Section II. 



" Work done under Contract NR-015-318 between the Office of Naval 

 Research, Department of the Nav>', and the Florida State University. 



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