Organic Room-Temperature Phosphorescence of Layered Organic Ammonium Chloride via Layer-By-Layer Assembly

Room-temperature phosphorescence (RTP) from organic ionic crystals mainly related to molecular packing has attracted growing attention over a wide range of advanced applications. However, limited research has focused on improving the RTP performance of organic materials in their aggregated state. Herein, we utilize the layer-by-layer self-assembly of organic ammonium chloride salts to enhance the macroscopic performance and increase the phosphorescence lifetime by 1-2 orders of magnitude. Especially, the millimeter-sized large organic ionic crystal exhibits an obvious RTP emission (insensitive to air) with an ultralong lifetime of 1886 ms, exceeding most counterparts. Molecular dynamics simulations reveal that the compact intermolecular stacking isolates oxygen molecules from the phenyl groups (distributing the spin population in the triplet state), which effectively suppresses triplet quenching for large crystals. Furthermore, other organic ammonium chloride salts also confirm such a macrocrystal-sized dependence on phosphorescence lifetimes. This work provides an effective crystallization strategy to realize an ultralong RTP emission, along with an extensive modulation of luminescence lifetime potential for time-gated encryption.