Color-Tunable Long-Afterglow Materials Constructed by a Zinc Coordination Polymer or an Organic Cocrystal: Design, Syntheses, and Dual Applications in Information Encryption and Anti-Counterfeiting

Abstract

The stimuli-responsive, multifunctional long-afterglow materials represent a pivotal direction for advancing information security and anti-counterfeiting. Herein, this study presents the design and syntheses of two long-persistent luminescent materials: a zinc coordination polymer, [Zn(bpy)(HIPA)₂]_n (1, bpy = 4,4′-bipyridine; IPA = isophthalate), and an organic cocrystal, (bpy)·2(H₂IPA) (2), constructed from isophthalic acid and 4,4′-bipyridine. Both compounds exhibit dual-mode long-lived luminescence, room-temperature phosphorescent (RTP), and delayed fluorescence (DF), especially color-tunable afterglow. Notably, 1 demonstrated a significantly prolonged afterglow duration of 6 s, highlighting the critical role of metal coordination in enhancing the phosphorescence lifetime and outperforming most IPA-based luminescent compounds. Single-crystal X-ray diffraction analysis confirmed that zinc (II) ions and ligands constructed a more rigid 1D coordination polymer via the linkage of bpy, which effectively suppressed non-radiative decay induced by molecular vibration and rotation. Density functional theory (DFT) calculations confirm the existence of metal−ligand charge transfer (MLCT) and ligand−ligand charge transfer (LLCT) in 1 and charge transfer (CT) and local excitation (LE) in 2, which are responsible for the excitation-wavelength-dependent emission of 1 and 2. Leveraging their exceptional dynamic luminescence, a time-gated information encryption and multi-level anti-counterfeiting system was developed. This work not only elucidates the structure−property relationship governing phosphorescent behavior but also provides a novel strategy for developing multifunctional materials integrating information encryption and anti-counterfeiting.