A super-stable Cu(i)-based polymer exhibiting thermally activated delayed fluorescence and water/acid-resistant properties

Abstract

Thermally activated delayed fluorescence (TADF) materials have attracted increasing attention due to their promising applications in efficient organic light emitting diodes (OLEDs). However, synthesizing ultra-stable luminescent materials remains a challenge. Herein, we report a novel, ultra-stable “butterfly” shaped Cu(I)-based coordination polymer, Cu_nI_n(PNP)_n/2 (PNP = 2,6-bis(diphenylphosphino)pyridine), featuring both staggered triangular and tetrahedral configurations. This polymer exhibits efficient yellow emission with a photoluminescence quantum yield (PLQY) of 58% at ambient temperature. Experimental and theoretical investigations reveal that a small ΔE_ST value (0.071 eV) enables Cu_nI_n(PNP)_n/2 to demonstrate 89% TADF properties with a short decay time of 9.34 μs at room temperature. Notably, reversible mechachromism was detected in Cu_nI_n(PNP)_n/2, with PL switching between yellow and orange–red emissions upon grinding and acetonitrile treatment. The formation of multiple hexagonal chelating rings facilitated by tridentate ligands, along with a short Cu–Cu distance of 3.05–3.168 Å, enhances metal–metal interactions, resulting in superior water and acid resistance. Moreover, leveraging its efficient TADF properties and stability, we fabricated a down-conversion white LED (WLED) device based on Cu_nI_n(PNP)_n/2. This work enhances our understanding of ultra-stable Cu(I)-based TADF materials for potential solid state lighting (SSL) applications.