6. Excitations and the Biological Matrix 



The first question that needs to be answered in connection with 

 the experiments described in the previous chapter is that about the 

 role of water which, together with the low temperatures employed, 

 so completely changed the situation. The results make it clear that 

 the effect of water and cooling was not additive but the two did 

 something specific together. Water, in itself, does nothing, and 

 cooling, in itself, does nothing, for at room temperature the situa- 

 tion is not changed by using water as a solvent instead of glycerol, 

 while cooling does not change the situation if glycerol or a 10% 

 watery glycerol is used as a solvent. That temperature, as such, is 

 ineffective is also borne out by the fact that the behavior of rho- 

 damin or riboflavine is essentially identical whether we use dry ice 

 or liquid N2 for cooling, though there is more than 100°C differ- 

 ence between the temperature of the two. So evidently, something 

 new and specific had to be produced by the introduction of water 

 and cooling. This could hardly be anything else than the forma- 

 tion of ice. That this is actually so is borne out by the temperature 

 dependence of the observed phenomena. We must distinguish here 

 between two reactions: the excited molecule's going into the trip- 

 let state and its emitting phosphorescent light. The two depend 

 on temperature in a different way. A rhodamin solution, for in- 

 stance, cooled to — 78°C shows a v^eak red light emission. If al- 

 lowed to warm up gradually, the light emission fades out around 

 — 40°C. From —40° upwards there is no phosphorescence and 

 'until the ice does not melt there is no fluorescence either. There 

 is no light emission at all. Fluorescence sets in only when the ice 

 starts to melt. Thus the triplet is stable until the ice does not 

 melt. We do not need the strong and rapid cooling in our ex- 



32 



