Multi-component emission spectra in toluene–diamine systems

Abstract

The fluorescence spectra of intermolecular and intramolecular toluene–amine and toluene–diamine systems were measured in THF. The fluorescence spectrum of toluene–N,N,N′,N′-tetramethyl-1,4-butanediamine (TMBD) mixtures was decomposed into four component bands with the shortest-wavelength band (band A) assigned to the excited toluene. Of the remaining bands, the short-wavelength (band B), the middle-wavelength (band C) and the long-wavelength band (band D) were assigned to a locally excited amine chromophore, an exciplex between toluene and an amino group, and an intramolecular excimer between two amino groups of the diamine, respectively. The fluorescence spectrum of toluene–TMBD mixtures in THF obtained upon nanosecond laser excitation showed a slight red shift with the time indicating that the contribution of band D increased with time. A reaction scheme and energy level diagram were proposed for this system. In toluene–dimethylethylamine mixtures bands A–C were observed. While for 4-phenyl-1-N,N-dimethylaminobutane bands A–C were also observed, for 3-phenyl-1-N,N-dimethylaminopropane only band C was observed. In toluene–N,N,N′,N′-tetramethyl-1,3-propanediamine mixtures, only bands A and D were observed, and for N,N,N′-trimethyl-N′-3-phenylpropyl-1,3-propanediamine bands C and D were observed. Emissions from intramolecular exciplexes and excimers in which two chromophores are separated by three methylene groups were predominantly observed.