Dehydration-Triggered Afterglow Transition in a Mellitate-Based Coordination Polymer

Stimulus-responsive long persistent luminescence (LPL) materials have attracted wide attention due to their potential applications in information storage, anti-counterfeiting, optoelec-tronic devices, etc. However, LPL coordination polymers with room temperature afterglow transition characteristics have not been explored. Herein, mellitic acid and zinc ions were utilized to synthesize an acid-base stable coordination polymer (1) by an organic solvent-free hydrothermal method. 1 possesses a tightly stacked structure and exhibits dual-emission peaks with blue luminescence and blue-green afterglow. Upon exposure to heating, DMSO immersion, or vacuum, 1h, 1s, and 1v were obtained. The original blue luminescence changes to blue-green, while the afterglow turns yellow-green due to the loss of water molecules from the inner cavity. This is the first example of an LPL coordination polymer that can realize room temperature afterglow transition by dehydration operation. Moreover, the emission spectra of 1 can be recovered by exposing 1h, 1s, or 1v to water vapor, suggesting a reversible dehydration/hydration process. Experimental and density functional theory (DFT) results suggest that the fluorescence of 1 originates from the mixing of intra-ligand and ligand-to-metal charge transfer excited states. The triplet state from intersystem crossing is responsible for the long persistent luminescence of phosphorescence emission. The rational structural design along with the conceptual model of anti-counterfeiting and information encryption based on afterglow transition display the unique advantages of the LPL coordination polymer in realizing convenient multiple stimuli-responsive devices.

Automated summary

In this study, an acid-base stable coordination polymer (1) was synthesized using mellitic acid and zinc ions through an organic solvent-free hydrothermal method. 1 possesses a tightly stacked structure and exhibits dual-emission peaks with blue luminescence and blue-green afterglow. Room temperature afterglow transition can be achieved through dehydration operation, and the emission spectra of 1 can be recovered by exposing it to water vapor. The LPL coordination polymer has potential applications in information encryption and anti-counterfeiting due to its unique characteristics.