708 FLUORESCENCE OF PIGMENTS IN VITRO CHAP. 23 



mole/1, for dimothylamine in benzene, down to only 6.5 X 10~^ mole/1, 

 for piperidine in benzene. Water is about half as effective as piperidine. 



Although amines generally are the strongest activators, diphenylamine 

 and diphenylhydrazine are without effect. It is noteworthy that phenyl- 

 hydrazine acts as activator in low concentration, and as quencher in high 

 concentrations. 



The maximum intensity of fluorescence to which chlorophyll in a given 

 nonfluorescent solution can be raised by activators is independent of the 

 specific activator used, at least in the first approximation. 



Activation seems to be completely reversible; in other words, fluores- 

 cence disappears again if the activator is distilled away, and reappears 

 upon its renewed addition. 



Table 23.IIIA 



Efficiency of Activation of Fluorescence of a 5 X 10^*^ Mole per Liter Solution 



OF Chlorophyll a 



(after Livingston, Watson and McArdle, 1949) 



The fluorescence spectrum does not change significantly with progres- 

 sive activation. At least, in benzene-water mixtures, the positions of the 

 two band peaks are the same at F/Fo = 0.2, 0.8 and 1.0. As described 

 earlier, the absorption spectrum of chlorophyll does change with increasing 

 admixture of the activator (c/. fig. 21. 26, A and B). The absorption spec- 

 trum of a fully activated solution, although it is different from that of the 



