Deep-red ultralong room temperature phosphorescence of chitosan-based nanofibrous membrane activated by carboxylic acids

Organic non-conjugated materials with room temperature phosphorescence (RTP) have attracted increasing attention due to their fundamental importance and advantages like environmental friendliness, good biocompatibility, and various processing methods. However, most non-conjugated systems often suffered from the problem with very short RTP lifetimes in ambient conditions. Here, we proposed an efficient strategy to improve the RTP performance of chitosan (CTS) by constructing a strong ionic bond network based on carboxylic acids. The CA/CTS film prepared using citric acid (CA) as a solvent was found to emit a bright afterglow of about 5 s with a phosphorescence lifetime of up to 515 ms at 530 nm. Our experimental results indicated that forming synergistic networks of ionic and hydrogen bonding was a highly efficient method for achieving persistent RTP of CTS itself. Furthermore, due to the strong ionic interaction between 1-pyrenecarboxylic acid (PCA) and CTS, the PCA@CTS nanofibrous membrane with bright deep-red afterglow was first achieved through an electrostatic spinning technique using polyethylene glycol (PEG) or polyvinyl alcohol (PVA) as a co-spinning agent. This work not only offered a new kind of persistent RTP nanofibrous membrane but also gained a deeper insight into improving the phosphorescence properties of non-conjugated materials, especially natural polysaccharide.