Molecular Engineering of Photoacoustic Performance by Chalcogenide Variation in Conjugated Polymer Nanoparticles for Brain Vascular Imaging

As conjugated polymer nanoparticles (CPNs) have attracted growing interest as photoacoustic (PA) imaging contrast agents, revelation of the relationship between the molecular structure of conjugated polymers and PA property is highly in demand. Here, three donor–acceptor‐structured conjugated polymer analogs are designed, where only a single heteroatom of acceptor units changes from oxygen to sulfur to selenium, allowing for systematic investigation of the molecular structure–PA property relationship. The absorption and PA spectra of these CPNs can be facilely tuned by changing the heteroatoms of the acceptor units. Moreover, the absorption coefficient, and in turn the PA signal intensity, decreases when the heteroatom changes from oxygen to sulfur to selenium. As these CPNs exhibit weak fluorescence and similar photothermal conversion efficiency (≈70%), their PA intensities are approximately proportional to their absorption coefficients. The in vivo brain vasculature imaging in this study also demonstrates this trend. This study provides a simple but efficient strategy to manipulate the PA properties of CPNs through changing the heteroatom at key positions. The relationship between the chemical structure of conjugated polymers and the photoacoustic (PA) properties is investigated through molecular engineering in three donor–acceptor‐structured conjugated polymer‐based nanoparticles, where a single heteroatom change from oxygen to sulfur to selenium in the acceptor unit leads to significant differences in their PA signal output.