Breathing-induced high-temperature negative thermal quenching and room-temperature enhancement of luminescence in CuI–NC-based MOFs

Abstract

Negative thermal quenching (NTQ), particularly the high-temperature NTQ effect, is an extremely rare phenomenon occurring in luminescent materials because of the stringent conditions required for its manifestation. In this context, a thermally responsive copper(I)–iodide nanocluster-based metal–organic framework (MOF) was synthesized, which possessed a stable 3-fold interspersed structure and exhibited a near-infrared emission in air. Upon heat treatment at 400 K, a structural reconfiguration was induced by the expulsion of water molecules from the MOF. Notably, NTQ photoluminescence (PL) with a slight shift in the luminescence center was observed within the temperature range of 380–420 K. This effect was jointly triggered by the exhalation of guest molecules and electronic structural changes of ligands due to the single-crystal-to-single-crystal transformation. When cooled to room temperature, the dehydrated structure was still present, and the room-temperature phosphorescence (RTP) was significantly enhanced, approximately 5.8 times higher than the original phosphorescence. The duration of luminescence was extended to 17 times its original value. This alteration in PL was reversible when the MOF was exposed to ambient conditions (RT, 54% RH). This compound presents a new strategy for achieving high-temperature NTQ and modulating RTP using the dynamic behavior of CuI–NC MOFs, offering new insights into the realm of luminescent materials.