Electromagnetic Wave Absorption Performance Regulation of Crystalline Nickelphthalocyanine Covalent Organic Frameworks via Ionothermal Synthesis Temperatures

Highly efficient electromagnetic wave (EMW) absorption materials are urgently needed to protect electronic devices and to eliminate detriment for human beings. Here, it is demonstrated that crystalline covalent organic frameworks (COFs), nickel-phthalocyanine COFs (pNiPc COFs) can be used as highly efficient EMW absorption materials. Systematic investigations reveal that the electrical conductivities of pNiPc COFs can be regulated by the high ionothermal synthesis temperatures owing to the existence of carbonization, further exerting on the EMW absorption performances. A minimum reflection loss of -71.86 dB is obtained for the pNiPc COFs synthesized at 540 °C. Moreover, a maximum effective absorption bandwidth of 6.32 GHz against EMW radiation in the entire Ku band is achieved for the pNiPc COFs obtained at 520 °C. These excellent EMW absorption mechanisms arise from the synergistic effect of the orderly stacked frameworks with luxuriant heteroatoms and electrical conductivity derived from the existence of carbonization. This pioneered study not only provides guidance for designing and synthesizing crystalline COFs with highly efficient EMW absorption performance through straightforward synthesis strategy, but also highlights the requirement for exploring fundamental mechanisms behind interaction of EMW with crystalline COFs.