Solvent-Induced Morphology Control of Polymer Assemblies with Improved Photothermal Features

Organic photothermal agents (OPTAs) are extensively utilized in applications such as therapy and imaging. However, enhancing their photothermal performance often depends on complex molecular designs, which are limited by the challenges of chemical synthesis. Herein, we present a straightforward strategy to optimize the optical absorbance of OPTAs by adjusting the morphology of assemblies of an amphiphilic block copolymer (PEG₄₄-PTA₅), leading to enhanced photothermal conversion efficiency. By changing the polarity of the organic solvent in which the polymer was dissolved, addition of water to induce assembly led to the exclusive formation of polymersomes or bicontinuous nanospheres. The morphological variations were confirmed using a range of electron microscopy techniques and small-angle X-ray scattering. Due to their mesoporous structure, the bicontinuous nanospheres exhibited superior light-harvesting capabilities, achieving a high absorption coefficient of 1.1 × 10⁵ M^-1 cm^-1 and a photothermal conversion efficiency of 45% when irradiated with a 808 nm laser. Our work introduces a facile solvent-induced assembly strategy for precisely controlling the morphology of OPTAs while simultaneously tuning their light absorption properties to enhance photothermal conversion.