Nontraditional Organic/Polymeric Luminogens with Red‐Shifted Fluorescence Emissions

Nontraditional organic/polymeric luminogens, which do not contain any conventional chromophores like large pi-conjugated benzene rings and/or heterocycles, have attracted rapidly growing attention owing to their importance in the fundamental understanding of photoluminescence mechanisms and potential practical applications. However, compared to traditional luminogens, most nontraditional luminogens (NTLs) emit fluorescence in the blue region, and only very limited NTLs with green, yellow, and red emissions have been reported. It is of great scientific and practical importance to develop NTLs with red-shifted emissions and understand their mechanisms. This review first provides a brief overview of the types of NTLs based on heteroatoms in them, the luminescence mechanism and luminescent characteristics of NTLs, then summarizes recent progress in NTLs with red-shifted emissions and the main strategies employed, i.e., introducing multiple nonconventional chromophores, introducing intra-/intermolecular interactions to rigidify clusters, and introducing electron-giving/withdrawing groups into molecules to lower the gap between the HOMO-LUMO energy levels. This review also provides the perspectives and outlook on future development of NTLs with red-shifted emissions.