Nonaromatic Schiff Base Polymers With Red Fluorescence Emissions

ABSTRACT Nontraditional luminogens (NTLs) without aromatic groups or extended conjugation structures are of significance in elucidating fundamental photoluminescence (PL) mechanisms and enabling wide applications of organic luminogens. Unfortunately, most NTLs emit only in the low wavelength region. Here, we developed a novel type of organic NTLs through the Schiff base reactions between poly(allylamine) (PAA) and glutaraldehyde (GA) or glyoxal (GO) in solutions, followed by drying at room temperature or 60°C. The imine polymers exhibit excitation‐dependent fluorescence emissions, and their maximum emission wavelengths are in the range of 480 to 685 nm. Among them, the imine polymer prepared from PAA and GA by drying at 60°C shows the reddest fluorescence emission and the highest PL quantum yield (7.2%). The easier occurrence of Schiff base reaction between PAA and GA leads to the formation of more imine groups, which promotes through‐space conjugation (TSC) among imine groups, leading to more red‐shifted emission of the PAA/GA polymer than the PAA/GO polymer. The dialdehydes and the PAA aqueous solution can function as the invisible ink and selective developer, respectively, for information storage and encryption. This study provides a deeper understanding of the PL mechanisms of NTLs and guides the design of NTLs with red‐shifted emissions.