The temperature dependence of saturated amine fluorescence

Abstract

The temperature dependence of fluorescence intensity of several saturated amines was studied. For “flexible” amines such as triethylamine (TEA), dimethylethylamine (DMEA), triethylemine, tri- n-octylamine (TOA), and N-methylpiperidine (NMP), it was found that I f increased as the temperature was increased. For example, in DMEA, I f increases by a factor of ca. 77 between −100 and 100°C. These results are interpreted in terms of an activated configurational change from the initially-formed (nonfluorescent) state to a relaxed (fluorescent) state in these compounds. Activation energies for these conversions range from about 1.8 kcal/mole for TOA to about 4.3 kcal/mole for TEA. Rigid, bicyclic amines having bridgehead N-atoms such as 1-azabicyclo [2.2.2] octane (ABCO) and its [3.3.3] analog were found to have temperature independent fluorescence intensities. These results were assumed to reflect the difference in energetics between the initially-formed and relaxed states relative to the “flexible” amines.