Thermal-induced coloration and photothermal conversion of an Ag-based coordination polymer with stable radicals

Abstract

In this work, an exceptional crystalline material only composed of non-radical components exhibits significant charge transfer under ambient conditions. Remarkably, even after subjecting the crystals to high-temperature treatment at 400 °C, the presence of organic radical species is still observed. Meanwhile, exposure to high temperatures (≥330 °C) induces notable modifications in the band gap, leading to a striking color transition from the original yellow to a deep black, accompanied by variations in spectral properties and photothermal conversion characteristics. The strong lone pair–π interactions between different moieties in the crystal play a crucial role in providing pathways for charge transfer and contributing to the formation of long-lived charge-separation state at room temperature. More importantly, the unpaired electrons can be effectively delocalized over the entire matrix through the lone pair–π interactions, resulting in the observation of “stable” organic radicals in crystalline solids. Significantly, the investigation of temperature-dependent single crystal reveals that the high temperature will cause longer lone pair–π distances, which result in a reduction of the amount of stable organic radicals in the crystal.