A π-π stacked porous framework for highly efficient second near-infrared photothermal effects and photo-thermo-electric conversion

Near-infrared (NIR) photothermal compounds, which convert low-energy NIR photons into heat, have recently attracted significant attention due to their potential applications in many areas such as photothermal imaging, diagnosis and therapy, photosensors, and catalysis. Photothermal conversion efficiency (PCE), a critical parameter of NIR photothermal materials, significantly influences their practical performance. However, exploring highly efficient NIR photothermal compounds, particularly in the NIR-II domain, remains a significant challenge. Herein, we report on a highly efficient NIR-II photothermal compound based on a novel pi-pi stacked porous framework {[Ni4Cl2(ONDI)(2)(bpy)(4)]& sdot;2Cl & sdot;2H(2)O & sdot;xDMF & sdot;yH(2)O}(n) (1). This compound features a porous supramolecular framework constructed through intermolecular pi-pi interactions. Additionally, compound 1 exhibits broad optical absorption spanning from the ultraviolet to the NIR region, with an edge extending to 1600 nm. Under irradiation with a 1064 nm laser, compound 1 demonstrates significant NIR-II photothermal effects, achieving a remarkable PCE of 84.4 %, attributed to the formation of charge states and the abundant pi-pi interactions in its crystal structure. When integrated with commercial thermoelectric generators, compound 1 shows promising potential for photo-thermo-electric conversion, with a maximum open-circuit voltage of 250 mV and 350 mV under irradiation of 1 sun and 2 suns, respectively. Furthermore, the output power density of 1@TEC1-12701 reaches 0.53 W/m(2) under 1 sun and 1.23 W/m(2) under 2 suns.