Organic Charge-Transfer Cocrystals toward Large-Area Nanofiber Membrane for Photothermal Conversion and Imaging.

Organic photothermal materials integrating a high-efficiency light-heat conversion effect and high flexibility have generated immense interest in fundamental research and practical applications. Nevertheless, their practical applications still remain a challenge, owing to the complicated design, tedious synthesis, and limited programmable substrates. Herein, an organic charge-transfer cocrystal with a narrow energy gap of 0.33 eV and a high photothermal conversion efficiency (PCE) of 69.3% was rationally designed and synthesized via a facile self-assembly process, which was introduced into polyurethane for forming a large-area photothermal nanofiber membrane via electrospinning technology. Femtosecond transient absorption spectroscopy elucidates that the excellent PCE is attributed to the nonradiation transition process, including internal conversion and charge dissociation processes. Furthermore, the temperature of the as-prepared photothermal nanofiber membrane could quickly rise to 52 °C under laser irradiation with a power density of 0.183 W/cm, suggesting a high PCE of 53.7%. This work successfully achieves the fabrication of a large-area photothermal membrane and the development of photothermal imaging.