Thermally Activated Fluorescence vs Long Persistent Luminescence in ESIPT-Attributed Coordination Polymer

Area of Science:

• Materials Science
• Photochemistry
• Coordination Chemistry

Background:

• Excited-state intramolecular proton transfer (ESIPT) molecules enable photoluminescence (PL) switching, crucial for displays, sensing, and imaging.
• Coordination polymers with ESIPT properties are underexplored, particularly those exhibiting alternative PL between thermally activated fluorescence (TAF) and long persistent luminescence (LPL).

Purpose of the Study:

• To report the first ESIPT-attributed coordination polymer with switchable TAF and color-tuned long persistent luminescence (LPL).
• To investigate the mechanism behind the TAF/LPL switching in a dynamic Cd(II) coordination polymer.

Main Methods:

• Assembly of a dynamic Cd(II) coordination polymer (LIFM-101) using an ESIPT-type ligand (HPI2C).
• Temperature control to achieve TAF and/or color-tuned LPL.
• Experimental and theoretical investigations into intersystem crossing (ISC), reverse intersystem crossing (RISC), and internal conversion (IC) processes.

Main Results:

• Successful synthesis of LIFM-101, a dynamic Cd(II) coordination polymer from the HPI2C ligand.
• Demonstration of temperature-controlled switching between TAF and color-tuned LPL.
• Identification of mixed higher-energy excited states due to the ligand's twisted structure, facilitating energy transfer and enabling the TAF/LPL switching mechanism.

Conclusions:

• A novel ESIPT-attributed coordination polymer (LIFM-101) exhibiting unprecedented TAF/LPL switching has been developed.
• The study elucidates the crucial role of excited-state dynamics, including ISC, RISC, and IC, in this switching behavior.
• This work provides a foundation for designing advanced optical materials with tunable luminescence properties.