Quenching of aromatic hydrocarbon fluorescence by α,ω-diamino-alkanes

Abstract

α,ω-Bisdiethylamino-, α,ω-dipyrrolidino-, and α,ω-dipiperidino-alkanes quench the fluorescence of aromatic hydrocarbons in cyclohexane solution. The efficiency of quenching is dependent upon the length of the chain linking the two nitrogen atoms. For chains containing <6 methylene groups, quenching is proposed to occur via a complex in which both nitrogen atoms interact with the aromatic hydrocarbon. Spectroscopic evidence for the formation of such complexes is presented. Complex formation markedly attenuates the quantum yield of exciplex fluorescence. For daimines having >6 methylene groups linking the nitrogen atoms, quenching is proposed to occur via a multi-collisional process. These diamines are more effective quenchers than their monoamine counterparts. The effect of chain length is barely noticeable when solvents more polar than cyclohexane are used. α,ω-Bis(N-methylanilino)-alkanes are efficient quenchers of aromatic hydrocarbon fluorescence, but the efficiency does not depend on the length of the linking chain. The quantum yield of exciplex fluorscence is attentuated when the linking chain contains two or three methylene groups.