ACTIVATION OF FLUORESCENCE 



767 



could perhaps be due to residual moisture (or other polar admixtures). 

 Addition of 0.01% water (6 X 10"^ mole/1. HoO) brought F back to the 

 usual level, Fo- 



Other solutions that proved nonfluorescent were those in n-heptane, 

 iso-octane, styrene, chlorobenzene, carbon tetrachloride and diphenyl 

 ether. Solutions in methanol, ethanol, octanol, dimethyl ether and diethjd 

 ether, on the other hand, remained fluorescent even after drying. It was 



Fig. 23.6. 



IQ-'^ 2x10"'* 



MOLALITY OF ACTIVATOR 



Intensity of fluorescence of chlorophyll a in a hydrocarbon as function of 

 the concentration of an activator (after Livingston 1948). 



Curve number 1 2 3 4 5 



Solvent n-Heptane Benzene Benzene Isooctane Benzene 



Activator Phenylhydrazine Benzyl alcohol Cetyl alcohol Methanol Piperidine 



Chlorophyll ... a a or 6 a a a 



considered possible, however, that the fluorescence in the last two solvents 

 was due to residual impurities. 



Figure 23.5 shows the intensity of fluorescence as function of composi- 

 tion in a mixture of benzene and octanol. The fluorescence is completely 

 activated by 0.0016 mole alcohol in a mole of hydrocarbon, corresponding 

 to a concentration of about lO"^ mole/1. Similar relationships were found 

 in mixtures of benzene wuth other polar solvents — alcohols and amines. 

 Figure 23.6 shows the initial parts of five activation cui-ves. Table 23.IIIA 

 gives, under [Ac]i/j, the molar concentrations of the activators needed to 

 raise the fluorescence intensity to V2 ^0; they range from 6.8 X 10 "^ 



