Enhancing\nNear-Infrared Photothermal Performance by\nMolecular Aggregation Optimization in Semiconductive Coordination\nPolymers

Near-infrared (NIR) photothermal conversion materials\nhave recently\nreceived widespread attention due to their potential in diverse applications.\nHowever, highly efficient organic-based NIR photothermal agents remain\nlimited. Developing strategies to enhance the efficiency of NIR photothermal\nmaterials and elucidating the relationship between the NIR photothermal\nperformance and molecular aggregation are highly desired. Herein,\nwe report two coordination polymers {[Cd<sub>2</sub>(ONDI)(ox)]·2/3(H<sub>2</sub>O)}<sub><i>n</i></sub> (<b>1</b>) and [Ba(ONDI)(H<sub>2</sub>O)<sub>2</sub>]<sub><i>n</i></sub> (<b>2</b>), in which the ONDI<sup>2–</sup> ligands assemble into different\nπ–π stacking arrangements. Compound <b>1</b> exhibits H-aggregation, while compound <b>2</b> displays X-aggregation.\nThe X-aggregation in compound <b>2</b> extends the optical absorption\ninto the NIR region and enhances the absorption intensity. Consequently,\ncompound <b>2</b> demonstrates a 1.8-fold increase in NIR photothermal\nefficiency (68.6%) compared to compound <b>1</b> (38.8%), attributed\nto more effective π–π interactions in X-aggregation.\nIn addition, both compounds show semiconductive properties, with conductivities\nof 2.1 × 10<sup>–7</sup> S/cm for compound <b>1</b> and 3.0 × 10<sup>–7</sup> S/cm for compound <b>2</b> at 30 °C in a nitrogen atmosphere. These properties arise from\nthe synergistic effects of “band-like” charge transport\nwithin crystals and “hopping” charge transport across\ngrain boundaries. By integration of their NIR photothermal effects\nand semiconductive properties, compounds <b>1</b> and <b>2</b> show interesting NIR photoelectrical responses.