The excitation-dependent/independent fluorescence in non-traditional simple emissive Amines: Structure, mechanism and application

In recent years, non-traditional intrinsic luminophores (NTILs) have garnered significant attention due to their ability to produce bright fluorescence after simple treatments. In this study, by employing a straightforward methodology of oxygen purging and controlled thermal treatment (40–120 °C), we demonstrated that non-traditional small-molecule amines (mainly diethylenetriamine, DETA) can exhibit rare dual fluorescence characteristics, including excitation-independent (EIF) and excitation-dependent (EDF) behaviors. More importantly, through structure characterization, fluorescence lifetime analysis, and simulation calculations, we confirmed the following structure-mechanism relationship underlying DETA luminescence: when pure DETA molecules were heated within the 40–80 °C, a stable dimeric structure (DETA-dimers) formed through hydrogen-bond interactions resulted in fluorescence centers exhibiting EIF characteristics. Notably, when the temperature increased further (80–120 °C), DETA-dimers in their excited state interact with oxygen molecules under external light, which formed dynamic excimers through space conjugation, denoted as [DETA-dimer … O 2 ], resulting in EDF phenomenon. Finally, capitalizing on DETA dual fluorescence properties, we successfully implemented EIF-based ion detection and EDF-enabled fluorescence staining applications. Consequently, this work advanced the mechanistic understanding of NTILs' intrinsic luminescence and established a framework for optimizing their performance in high-sensitivity fluorescence imaging and probe development.