404 



PHOTOMECHANICAL CONSIDERATIONS 



BChl + O 



BChlO, 



2 '^2 



spectrum Fig. 2 

 The chemical back reaction with ascorbic acid: 

 BChl^ + a. a. + H^- 



•-BChl' + a.a/ + HgO 



chemiluminescence 

 BChl' *- BChl 



A chemiluminescence in the spectral region of bacteriochlorophyll 

 fluorescence indeed is measured upon addition of ascorbic acid to 

 photobleached bacteriochlorophyll solutions (Fig. 7), This addition is 

 successful up to 30 minutes after bleaching. If ascorbic acid is added 

 before the onset of illumination, a photooxidation of this compound, 



Luminescence 

 (rel units ) 



0.5 



Fig. 7. Chemiluminescence due to addition of ascorbic acid 

 to photobleached bacteriochlorophyll (added 10 minutes after 

 bleaching) and chemiluminescence due to illumination of 

 bacteriochlorophyll-ascorbic acid mixtures. 



measured as oxygen uptake during illumination, as well as an emission 

 of chemiluminescence, is observed. Part of the electron energy stored 

 in ascorbic acid thus appears to be emitted as chemiluminescence. 



