Emission properties of (2-pyridyl)-(CH2),-(2-pyridyl)(n= 2, 3, 5, and 7) and (4-pyridy1)-(CH2),- (4-pyridylJ (n= 2, 3, and 5) were studied in solution in the presence of trifluoroacetic acid at room temperature and 77 K. At room temperature, only 1, 3-di (2-pyridyl) propane exhibits a very weak fluoroescence at approximately 6900 cm-'to the red of the normal fluorescence. This band is ascribed to an intramolecular excimer fluorescence between the protonated ...
