Diradical-Featured Organic Small-Molecule Photothermal Material with High-Spin State in Dimer for Ultra-Broadband Solar Energy Harvesting.

Organic materials with radical characteristics are gaining increasing attention, due to their potential implications in highly efficient utilization of solar energy. Manipulating intermolecular interactions are crucial for tuning radical properties, as well as regulating their absorption bands, and thus improving the photothermal conversion efficiency. Herein, we report a diradical-featured organic small-molecule croconium derivative, CR-DPA-T, for highly efficient utilization of solar energy. Upon aggregation, CR-DPA-T exists in dimer stablized by the strong intermolecular π-π interactions, and exhibits rarely reported high-spin state. Benefiting from the synergic effects of radical characteristics and strong intermolecular π-π interactions, CR-DPA-T powder absorbs broadly from 300 to 2000 nm. In-depth investigations with transient absorption analysis reveal that the strong intermolecular π-π interactions could promote non-radiative relaxation by accelerating internal conversion and facilitating intermolecular charge transfer (ICT) between dimeric molecules to open up faster internal conversion pathways. Remarkably, CR-DPA-T powder demonstrates a high photothermal efficiency of 79.5% under 808 nm laser irradiation. By employing CR-DPA-T as solar harvester, a flexible H-PDMS/CR-DPA-T self-healing film is fabricated and employed for solar thermal applications. These findings provide a feasible guideline for developing highly efficient diradical-featured organic photothermal materials. This article is protected by copyright. All rights reserved.