MELl/X CALVIN 



333 



of the pigment, and this molecule has some resemblance to the por- 

 phyrin structure previously discussed. There are major differences, 

 however, which nuist be kept in mind: the bridging atoms in phthalo- 

 cyanine are nitrogen atoms instead of carbon atoms, and fused onto 

 each of the pyrrole rings is a benzene ring which, of course, changes 

 the nature of the compound considerably. It happens that I became 

 familiar with this molecule in 1937, shortly after its discovery by 

 Linstead, and participated in the demonstration of some of its cataly- 

 tic abilities at the same time that Eley was working with it (16, 17) . 

 Eley has gone on to examine the electrical properties of phthalo- 

 cyanine, and in recent years we turned to this also. 



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PHTHALOCYANINE 



Fig. 10. .Structural foiinula of phthalocyanine. 



Phthalocyanine is a very stable substance, easy to prepare and not 

 easy to destroy (compared to chlorophyll), and we have used it as 

 a model in our photophysical measurements. The first experiments 

 undertaken were to demonstrate the effect of electron acceptors, or 

 electron donors, added to crystalline phthalocyanine, on its con- 

 ductivity and its photoinduced conductivity. These experiments were 

 one step beyond what Vartanyan and Eley had done. They studied 

 primarily the behavior of what they believed to be the pure 

 phthalocyanine. 



We made layers of phthalocyanine on a conductivity cell and then 

 added electron donors or acceptors to it to see what effect these would 

 have on the electrical conductivity in the dark and on the photo- 



