174 LIGHT AND LIFE 



in a-tetralone and water (6, 3) . We may therefore write (* signifies 

 an electronically excited molecule) : 



* 



Porphyrin 



I ^ + H + [porphyrin] 



2 



If this (strongly exergonic) reaction is run backward, water is split 

 and a hydroperoxide is obtained. In purely formal terms, at least, 

 this corresponds to a reaction of the general type that might be looked 

 for in plant photosynthesis, although it is emphasized that the equili- 

 brium point of the process written above must lie far to the right. 

 In this paper we wish simply to point out such possible relationships. 

 Our chief concern at this time is with the mechanism whereby the 

 porphyrin becomes electronically excited. 



A preliminary kinetic study of the chemiluminescent decomposi- 

 tion of THP, catalyzed by zinc tetraphenylporphine (ZnTPP) , was 

 reported by Linschitz and Abrahamson (9) . We briefly summarize 

 here the results of further work on the reaction in our laboratory. 



Experimental 



Kinetic and luminescence measurements were made on solutions 

 of THP and ZnTPP in ^butyl benzene. Reagents and solvents were 

 highly purified. Samples were degassed on the vacuum-line and the 

 reaction run in sets of sealed-off tubes, at temperatures between 135° 

 and 155°C. At suitable intervals, a tube was withdrawn from the 

 thermostat, quenched, and its contents analyzed for peroxide 

 (iodimetrically) and for porphyrin (spectrophotometrically) . Dur- 

 ing the course of the reaction, the decay of the chemiluminescence was 

 followed by a photomultiplier photometer, in which the liniiinescence 

 intensity was compared with the light output from a standard lamp. 



Results 



The general featvnes of the reaction and luminescence kinetics are 

 given in Figs. 1 and 2, which show respectively the time course of 

 peroxide and porphyrin concentration, and of the chemiluminescence 

 for a typical run. For comparison, an inicatalyzed peroxide decomposi- 

 tion is also shown in Fig. 1. Table 1 presents smoothed concentra- 



