27 



brilliant orange fluorescence of this dye, while the lower frozen 

 half shows practically no light emission at all. Ample evidence 

 will be supplied later to show that this change is not due to the 

 dye molecules having become inexcitable nor to their dissipating 

 the energy of their singlet excitation. They are just as excitable as 

 before (as shown by the almost unchanged color) and do not 

 dissipate their energy (the low temperature and solid state also 

 disfavors such dissipation). The change is due to the excited 

 electrons going into the "forbidden" triplet state. The peculiar 

 conditions prevailing in our frozen water make this transition not 

 only an allowed one but the most probable one, and so the elec- 

 trons go into it wholesale. 



The second tube from the left in Fig. 6 contained the same 

 watery rhodamin solution as the first one, with the difference that 

 at the side of the dye also 10~^ M thiamine hydrochloride was dis- 

 solved in it. The unfrozen solution in the upper half shows the 

 same orange fluorescence as before. The difl?erence is in the frozen 

 part. This shows an intense red light emission, comparable in its 

 intensity to the fluorescence of the unfrozen solution. The light 

 emission is red, of longer wavelength (and lower energy) than 

 the orange fluorescence. In the fast phosphoroscope this frozen 

 part of the tube shows luminescence which indicates that the 

 emitted red light comes from a triplet state and is due to the re- 

 turn of the excited electrons from their excited triplet into the 

 ground state. So water, in presence of thiamine, makes this transi- 

 tion possible too, promoting the transition both ways, from singlet 

 to triplet and from the triplet to the ground state. 



There are two facts emerging from this experience: that water 

 can promote the singlet ^ triplet transitions and that the proba- 

 bilities of these transitions can further be modified by added sub- 

 stances. Thus the transitions are accessible to regulatory influences 

 and if these excitations would play a major role in biology they 

 could be controlled by hormones, modified by drugs, or might be 

 disturbed under pathological circumstances, giving rise to disease. 



