QUENCHING OF INTRA-MOLECULAR EXCIPLEXES BY PYRIDINE AND METHYLPYRIDINES SUGGESTING TRIPLE EXCIPLEX (D'DA) FORMATION

Intramolecular exciplex (DA) fluorescence of 1-(9,10-dicyano-2-anthryl)-3-(1-or 2-naphthyl)propane was quenched by pyridine and methylpyridines (D’). Double exponential decay of the intramolecular exciplex was observed at room temperature, while a single exponential decay of the exciplex in the 9,10-dicyanoanthracene and naphthalene system was observed. The result in the former system implies the formation of a new type of triple exciplex, (D'DA), including pyridine molecule, though neither new fluorescence nor transient absorption spectrum due to the triple exciplex was detected. Association and dissociation rate constants of (D'DA)* obtained in the intramolecular system decrease in the following order of the quenchers: pyridine > 4-methyl-> 3,5-dimethyl-> 2-methyl-> 2,6-dimethylpyridine. These results suggest that the non-bonding orbital of a nitrogen atom in a pyridine ring may play an important role in the ferelectronic interaction, (D'DA)*, in the excited state. © 1979, American Chemical Society. All rights reserved.