86 



an afterglow was produced by the addition of 1-2% glucose to 

 the watery dye solutions previous to their freezing. Other mono- 

 and disaccharides, such as ribose, galactose, mannose, fructose, 

 saccharose, or maltose acted similarly, while high polymers such 

 as dextrin, starch (soluble or insoluble), or agar had no such 

 action. A tentative explanation is suggested by a simple experi- 

 ment: if a dye solution is placed in a test tube and is frozen slowly 

 (e.g., by placing it in the deep freeze at — 20°C), a sheet of 

 colorless ice is formed in the periphery while the dye is concen- 

 trated in the middle. Evidently, the water crystallized out leaving 

 the dye behind. If, prior to freezing, 1-2% sugar is added to the 

 solution, the dye is found more or less homogeneously distributed 

 in the ice. The sugar, so to say, mediates between ice and dye, 

 making the contact between the two more intimate. If it is the 

 water structure which enables the dye to form triplets, then the 

 probability and stabilit}^ of the triplets must be the greater the 

 more intimate the contact between dye and ice. 



The sugar molecules can be expected to build their own "ice- 

 bergs." In the above experiment these icebergs must have fitted 

 into the water lattices formed on freezing, or else the sugar would 

 have also been eliminated by the freezing water. This system of 

 ice and sugar-icebergs accommodated the dye molecules better than 

 pure ice. How^ever, the glucose added favored not only phospho- 

 rescence but caused also a strong fluorescence to appear. While a 

 pure rhodamin solution shows no fluorescence at all, in presence 

 of 1-2% glucose the frozen dye shows on illumination, at the 

 side of phosphorescence, also a strong orange fluorescence, which 

 blends with the red phosphorescence to a red-orange glow. The 

 higher the sugar concentration the stronger the fluorescence. 

 While in the presence of 1% glucose the emission is red-orange, 

 in the presence of 10% glucose it appears purely orange and the 

 strong phosphorescent component can be seen only in phosphoro- 

 scope which does not allow the fluorescent light to pass. So glucose 

 seems not only to stabilize the triplet. In a way it seems to render 



