Oxidation-induced and dimer-structured clusteroluminescence for simple emissive amine molecules: Mechanism of non-traditional intrinsic luminescence

Abstract

Non-traditional intrinsic luminescence (NTIL) substances have received a lot of attention because of their unique fluorescence properties in recent years. However, the NTIL molecules actually do not contain any aromatic or extended π-systems, therefore the relationships between luminous structure and emissive mechanism are still extremely debatable. In view of the above problems, this paper used small molecular amines (mainly triethylamine, TEA), a basic representative of nitrogen-containing NTIL molecules, as a template to study the structure and mechanism of NTILs. By circular treatment of reflux/distillation, careful analysis of the structural characterization coupled with theoretical calculations, we demonstrated that the optical properties of TEA were strongly related to oxygen molecules. Particularly, our data indicated that oxygen molecules induced a weak hydrogen bond between TEA molecules to form a dimer structure, meanwhile, the robust TEA-dimer and oxygen molecules were through n-π electron delocalization space conjugated to form an N⋯O clusteroluminogens. This physical bonding and spatial conjugate fluorophore structure not only well explains: why such nitrogen-containing NTIL substances lack normal organic conjugate structures and exhibit abnormally bright fluorescence in the visible spectrum when exposed to oxygen molecules (a traditional organic fluorescent material quencher), but also has important implications for further elucidating some tissue biofluorescence from oxidative folding of proteins.