Manipulating Molecular Conformation of Charge-Transfer Cocrystal for Nir-Ii Absorption and Light/Thermal-Responsive Imaging

Abstract

Organic photothermal materials, renowned for their efficient light-to-heat conversion and high flexibility, have garnered significant interest in stimuli-responsive applications. However, challenges such as complex synthesis, restricted absorption, poor stability, and low photothermal conversion efficiency (PCE) terribly impede their practical application. This study presents an organic charge-transfer (CT) cocrystal with a broad NIR-II response (250 to 2050 nm), which was synthesized using a tetrathiafulvalene donor with a freely rotating π-conjugate group. This cocrystal is integrated into polyurethane to create scalable photothermal nanofiber membranes via cost-effective electrospinning technology. The free rotation of the benzene ring enhances nonradiative recombination, leading to a high PCEs of 81.7% for the CT cocrystals, and 62.8% for the resulting nanofiber membrane. Furthermore, coating with reversible thermochromic microcapsules endows the nanofiber membrane with sensitive color changes from reddish-brown to light yellow under sunlight, or temperatures above 45 °C, suggesting promising applications in smart fibers for real-time photo-/thermos-stimuli-responsive imaging.

Keywords: organic photothermal materials, charge-transfer, NIR-II absorption, electrospinning method, stimuli-responsive imaging