Ultralong Afterglow of Zinc(II) Halide Complexes Enabled by Regulating the Arrangements of N-Methylbenzimidazole Ligands

Abstract

In this study, a simple and rapid strategy is developed for the gram-scale synthesis of zinc(II) halide complexes with ultralong afterglow under mild conditions. Crystalline, high-purity zinc(II) halide complexes are synthesized using N-methylbenzimidazole (Bz) and common zinc halide salts (ZnX₂, X = Cl, Br, and I) as simple and cheap industrial raw materials by stirring at room temperature and atmospheric pressure. By exploiting the steric effect of terminal-coordinated halogen ions to regulate arrangements of the Bz ligands in the structure of zinc(II) halide complexes, namely cis-butterfly, trans-butterfly, and cross-arrangement, zinc(II) halide complexes with completely differentiated stacking modes are obtained. Zn(Bz)Cl with a cis-butterfly-shaped arrangement of the Bz ligands has the longest room-temperature phosphorescence (RTP) lifetime (505.01 ms at 298 K) and a long afterglow of up to 1.4 s. This study proposes for the first time the use of differentiated halogen end group coordination to regulate the arrangement of fluorophores within the structure of zinc(II) halide complexes, resulting in considerably improved RTP and long afterglow, thus providing a new platform for the large-scale synthesis of simple complexes with room-temperature ultralong afterglow.