MEW IN CALVIN 335 



induced coiuluctivity (38, 39, 10). Fig. 11 shows such a conduc- 

 tivity cell with the electrodes, on top of which is placed a layer 

 of phthalocyanine. On top of that is laid the layer of electron ac- 

 ceptor. The results of experiments using such a conductivity cell 

 are shown in Fig. 12, where the solid line gives the effect of added 

 electron acceptor on the dark current. The dark current conduc- 

 tivity of such a sani})le, if electron acceptor is added, goes up as much 

 as seven powers of ten. The same type of thing is true of the photo- 

 induced conductivity, which goes up by as much as five powers of 

 ten as electron acceptor is added on top of the layer of the phthalo- 

 cyanine. I shall not try to review all of the kinetic and spectral 

 studies which have been performed on this phthalocyanine system, 

 but I shall sho^v only a few of the highlights and then present to you 

 what we believe to be the behavior of this molecular crystal in 

 electronic terms. 



\Vhen these electron acceptors were added to the phthalocyanine 

 layer, it was found that electron transfer took place, from the phthalo- 

 cyanine to the electron acceptor, even in the dark, as evidenced by 

 the presence of free-radical-like signals, determined by electron spin 

 resonance (ESR) , in such a "doped" or treated phthalocyanine sam- 

 ple (40). This is shown in Fig. 13, and the interesting fact is that 

 by treating (doping) the phthalocyanine with electron acceptor 

 (o-chloranil) we increase the dark current and also increase the light- 

 induced conductivity. When the light is turned on such a sample 

 as this, the number of unpaired electrons is decreased, as indicated by 

 the electron spin signal. Fig. 14 shows how this system behaves. 



Fig. 13. Electron spin resonance (ESR) spectrum of o-chloranil-"doped" phthalo- 

 cyanine. The curve represents the first derivative of the absorption. 



