23 



The electrons going into the triplet will have important con- 

 sequences. Firstly: the lifetime of the excitation will be greatly 

 lengthened, as a rule about a millionfold (Becker and Kasha). 

 The molecule, which contains the "uncoupled" electrons, will be 

 paramagnetic and will be in an unbalanced, more reactive state. 

 In many ways it will be akin to a free radical. 



If we want to study electrons in the triplet state we have to stabi- 

 lize them, protecting them as far as possible against deactivating 

 heat collision. This can be done by enclosing them in a rigid glass, 

 such as Borax. Cooling will help to some extent too, decreasing 

 heat agitation. We can combine the two and dissolve the substance 

 in question in a solvent such as glycerol and then freeze this sol- 

 vent by strong cooling in dry ice or liquid N2 to a rigid "glass." 

 By doing so we can increase the number of electrons present in the 

 triplet state. The more electrons in this state the greater the 

 chances that some will fall back directly to the ground state emit- 

 ting "phosphorescence." To show that the light actually is phos- 

 phorescence and not fluorescence, that it comes from a triplet, we 

 can observe the system in a phosphoroscope. This is an instrument 

 which cuts ofli alternately the exciting light going from the light 

 source to the phosphorescent material and the light going from 

 the phosphorescent material to the observer. If the time interval 

 between these two is 10"^ seconds, then light which the observer 

 sees must have been generated by an excitation which lasted 10"^ 

 seconds or more, was thus phosphorescence. Fluorescence only 

 lasts 10"* seconds or so. The author has used two phosphoroscopes 

 in his studies, a fast one with a time constant of 10"^ seconds and 

 a slow one which allowed light to pass only if coming from a 

 "long-life-excitation" lasting 0.1 second or more. 



There is one more point about the triplet state which might be 

 of prime import to biology, and this is that the probabilities of 

 the singlet-triplet transitions can be modified, are thus accessible 

 to regulatory influences. The probabilities of a singlet turning into 

 a triplet can, for instance, be greatly increased by the presence of 



