58 



LIGHT AND LIFE 



Quinvline (6) represents a case in which a blue-shift ot only a 

 very small part ot the long-wavelength absorption tail is observed as 

 one changes from hydrocarbon to ethanol solvent. However, a dra- 

 matic change in the low-temperature emission spectra in rigid glass 

 solvents is observed (6) : in the hydrocarbon solvent, a strong phos- 

 phorescence is observed, whereas in an ethanol-ether-isopentane glass, 

 fluorescence and phosphorescence are observed analogous to the emis- 

 sions of naphthalene. Thus, in this case, an actual interchange of the 

 electronic states of 7i,7r* and tt,tt* type must occur as the solvent is 

 changed. 



D. Pyrimidine and Purine 



The spectra of pyrimidine (26) are shown in Fig. 17. The lowest 

 n -^ 77* transition appears as a distinct band in the region of approx. 



WAVENUMBERS , CM" 

 45,000 40,000 35,000 



o 

 o 



2100 



2500 3000 



WAVELENGTH, A 



3400 



Fig. 17. Near ultraviolet absorption curses ol pyrimidine at room temjieralure, 

 after Mason (2(3). Cinve a. in (\clohexaiie; (in\e 1), in water (neiural); curve c, 

 in 4 iV sulfuric acid. 



