FLUORESCENCE SPECTRUM OE CHLOROPHYLL 



745 



Table 23.1 {Continued) 



C. BAND SHIFTS IN DIFFERENT SOLVENTS" 



Zscbeile and Harris (1943) 



Biermacher (1936) 



Chi. a, 



Solvent 



AX„ 



m/i 



Solvent 



Chi. o Chi. 6 



AX, m^ 



Methanol 10 



2-Ethylhexanol 10 



2-Methylpropanol 9.5 



Benzene 9 



Isopropyl ether 9 



Acetone 8.5 



1-Butanol 8.5 



Methyl oleate 8 



Carbon tetrachloride 8 



Olive oil 7.5 



Dioxane 7 



Cyclohexane 5.5 



Ethyl ether 4.5 



Pentane 4.5 4.5 



Hexane 4.5 4.5 



Pyridine 4.5 3.5 



Carbon tetrachloride 4 3 



Methanol 3.5 — 



Aniline 3 5 



Benzene 2.5 4.5 



Dioxane 2.5 5 



Ethanol 2.5 6.5 



Cyclohexanol 2 4 



Chloroform 2 2.5 



Carbon disulfide 2 6 



Acetone 1.5 8.5 



Ethyl ether 0.5 5 



Paraffin (liq.) 0.5 



" Photographic. 

 * Photoelectric photometer. 

 " Concerning subsidiary maxima, see page 748. 



<* Biermacher (1936) found no fluorescence at all in methylene iodide (as well as in 

 nitrobenzene). 



^ This figure is quoted by Seybold and Egle (1940) from Stern. 

 ^ After Stewart, Knorr and Albers (1942). 

 " AX = X(fluorescence) — X( absorption). 



with the true band maxima. He therefore denied that the difference be- 

 tween the X vahies measured by him and the X^ax. vahies found by earher 

 investigators covild have been due to the dechne in the sensitivity of his 

 photographic plates in the far red; he suggested instead that this differ- 

 ence was caused by the faihire of other observers to avoid "self-absorption," 

 i. e., reabsorption of fluorescent light befoi-e its escape from the chlorophyll 

 solution. (Because of the position of the fluorescence band of chlorophyll 

 close on the red side of the absorption peak, self-absorption must cause an 

 apparent shift of the fluorescence band maximum toward longer waves.) 

 The correctness of this interpretation was acknowledged by Zscheile and 

 Harris (1943), who made a spectrophotometric redetermination of the 

 fluorescence bands, varying the chlorophyll concentration systematically, 

 and using a capillary vessel to reduce self-absorption. The extent of the 

 self-absorption effect is illustrated by figure 23.3. It shows how large a 

 part of the fluorescence band is overlapped by the (shaded) absorption 

 band, and how, in consequence of this overlapping, the position of the 

 maximum of the fluorescence band can be displaced, by self-absorption, 

 by as much as 12 mju. The position of the second fluorescence band (at 720 

 m^) is found to be practically unaffected by reabsorption; this is natural, 

 since this band leads to a vibrating state of the chlorophyll molecule and 

 consequently does not occur in absorption — at least not with a marked in- 

 tensity. 



