CONCENTRATION QUENCHING 



775 



Numerous observations are known showing that the close packing of 

 chlorophyll molecules in solid chlorophyll, or in chlorophjdl monolayers on 

 water, causes a complete disappearance of fluorescence. Chlorophjdl 

 colloids too are, as a iiile, nonfiuorescent (Willstatter and St oil 1918; 

 Stern 1920, 1921; Albers 1935; Meyer 1939). Meyer described certain 

 fluorescent solutions of chlorophyll in ethanol as "colloidal," but no rea- 

 sons for this description were given (cf. Smith 1941). Meyer's aqueous 

 chlorophyll colloids, in which the density of the particles was similar to 

 that in the chloroplast grana, were nonfiuorescent. Chlorophyll is non- 



0.80 



0.60 



0.40 



10.20 



OOI 



002 



0.03 



0.04 



0.05 



O06 



0.07 



Fig, 23.7. Concentration quenching of fluorescence of chlorophyll a in butyl ether 

 (after Livingston and Ke, 1949). Ordinate, F/Fq. Abscissa, [Chi] in mole/1. 



fluorescent also in the adsorbed state, e. g., in starch columns used for 

 chromatographic separation (Sej-^bold and Egle 1940). 



If we attribute the nonfluorescence of solid, colloidal and adsoibed 

 chlorophyll to self-quenching, and consider it a consequence of close pack- 

 ing, the restoration of fluorescence by certain "protective" substances can 

 be attributed either to simple dilution of the pigment, or to effective inter- 

 mption of the interaction between neighboring pigment molecules. Among 

 the compounds reportedly capable of protecting the fluorescence of chloro- 

 phyll, we find first of all lipides and lipophilic solvents. Stern (1920. 



