BENTLEY GLASS 



861 



layer ol electron acceptor (ortho-chloranil) on lop ot it increases in 

 conclnctivity up to 10^ times in the dark and lO"" times in the light. 

 Electron transler was demonstrated by the presence of ESR (electron 

 spin resonance) signals. When the light is turned on, such a system 

 decreases in number ol unpaired electrons, to judge by the ESR 

 signal, while the conductivity increases. The observed phenomena arc 

 interpreted as signifying a transfer of electrons from phthalocyanine 

 to o-chloranil, so as to leave in the lattice positive ion radicals of 

 phthalocyanine which are responsible for the increased conductivity, 

 and to produce o-chloranil negative ion radicals carrying the inmio- 

 bile, trapped electrons. When 7000 A light is supplied, the exciton 



^^^ 



PHTHALOCYANINE 



Fig. 6. Structural formula of phthalocyanine. 



(combination of electron and positive hole in the lattice) can migrate 

 until ionization occurs. The niuuber of impaired spins is reduced 

 by the formation of the o-chloranil ion, but the conductivity of the 

 phthalocyanine is increased. When light of 4000 A is supplied, the 

 opposite happens. Electrons are then transferred from the o-chloranil 

 negative ion radicals to the phthalocyanine crystal lattice; each one 

 quickly combines with a positive hole, thus reducing the conductivity 

 but increasing the ESR signal. Since negative charge is trapped in 

 the o-chloranil layer and positive charge in the phthalocyanine layer, 

 there will be some polarization of the double layer. Light absorbed 

 by phthalocyanine will increase this polarization, so that photochemi- 

 cally one can induce a separation of oxidizing power, in the form of 



