Synthesis, Room-Temperature Phosphorescence Properties and Mechanisms of Aliphatic Polyamides with Different Carbon Chain Length

Polyamides, a class of polymer materials containing amide groups, are widely utilized for their outstanding mechanical strength, thermal stability, and processability. Recent studies have revealed that polyamides also exhibit room-temperature phosphorescence characteristics. However, the fundamental luminescence mechanism and the factors influencing their photo-physical remain unclear and require further investigation. In this research, a series of aliphatic polyamides are synthesized and a comprehensive investigation is conducted to elucidate the impact of carbon chain length on their photo-physical properties and the underlying mechanisms. As the carbon chain length of polyamides increases, their phosphorescence emission spectra first red-shift and then blue-shift, while the phosphorescence lifetime and quantum yield first increase and then decrease. Notably, even–odd polyamides show better phosphorescent luminescence performance compared to even–even polyamides. Among the synthesized polyamides, PA69 demonstrates the most favorable phosphorescence properties, with a lifetime of 1.22 s and a quantum yield of 15.98% at room temperature. This study reveals that the phosphorescence properties of polyamides are strongly correlated with their hydrogen bond content. As the carbon chain length increases, the hydrogen bond content initially increases and then decreases, leading to a corresponding trend in which both the phosphorescence quantum yield and lifetime first rise and then decline.