ENERGY TRANSFER IN PHOTOCHEMICAL SYSTEMS 57 



anthracene in naphthalene replaces the UV fluorescence of the naph- 

 thalene with the blue-violet anthracene fluorescence. The semiconduc- 

 tivity and photoconductivity of anthracene have been quite extensively 

 studied (Compton et al., 1957) and, of somewhat more biological 

 interest, similar studies have been carried out on the phthalocyanines 

 (Fielding and Gutman, 1957) 



A very interesting series of experiments (Borthwick et al., 1952; 

 Evanari and Stein, 1953; Evanari et al, 1953; Stein, 1954) on the 

 germination of seed by Hendricks and co-workers and by Evanari and 

 co-workers has shown that red light (5250-7000 A) stimulates such 

 germination whereas infrared radiation (7000-8200 A) reverses this 

 effect. These effects show a marked resemblance to phenomena ex- 

 hibited by many crystalline phosphors, and, in fact, the suggestion has 

 been made that these phenomena are the result of the formation of 

 trapped electrons in a semiconducting system by the action of the red 

 light and of the detrapping of the electrons by the infrared light. It 

 will be interesting to see if further experimentation supports this view- 

 point. 



ENERGY TRANSFER IN GREEN PLANT MATERIALS 



Katz, in 1949, and, independently, Bradley and Calvin, in 1955, 

 suggested that aggregates of chlorophyll molecules in the chloroplasts 

 might give rise to conduction bands in which photoproduced electrons 

 and holes could migrate. Such a system would have the advantage of 

 providing for a separation of the oxidizing and reducing entities known 

 to be necessary for photosynthesis. 



This concept remained purely speculative until, quite recently, a 

 number of researches have been published which sussest that some- 

 thing of this nature may indeed take place within chloroplasts. In 1956 

 Commoner and co-workers published evidence for the presence of a 

 light-induced electron spin resonance (ESR) in spinach chloroplasts 

 due to the photoproduction of unpaired electrons. Again, in 1957, 

 these co-workers showed the presence of two kinds of unpaired spins, 

 one of which is transformed into the other. In 1957 Arnold and Sher- 

 wood studied dried chloroplast films and found them to exhibit semi- 

 conductivity and thermoluminescence. In addition some studies by 



