Scalable Semi‐Aromatic Polyamides with Carbon‐Chain‐Regulated and Thermally Stable Cluster‐Triggered Room‐Temperature Phosphorescence

Room‐temperature phosphorescent (RTP) materials are attractive for applications in anti‐counterfeiting, bioimaging, and display technologies due to their long emission lifetimes and large Stokes shifts. In this work, a series of semi‐aromatic polyamide salts and their corresponding polyamides with varying aliphatic chain lengths are synthesized, and the influence of chain length on their photophysical properties is systematically investigated. All samples exhibit typical cluster‐triggered emission (CTE), with fluorescence red‐shifting as excitation wavelength increases. Both polyamide salts and homopolymers display structure‐dependent RTP, with phosphorescence emission blue‐shifting as chain length increases. Mechanistic studies reveal that hydrogen‐bonding content is the primary factor governing photophysical behavior. As the carbon chain length increases, hydrogen‐bonding content first rises and then falls, producing a corresponding volcano‐type trend in phosphorescence lifetime and quantum yield. Among them, PA8I exhibits optimal RTP, with a lifetime of 2.22 s and a quantum yield of 36.7%. The incorporation of aromatic rings imparts excellent thermal stability, with RTP remaining stable at 398 K and a lifetime of 0.38 s. Owing to mature synthetic protocols, low‐cost and readily available raw materials, these semi‐aromatic polyamides can be produced on a large scale, demonstrating both fundamental and practical potential for advanced RTP applications.