Semiconducting Polymers Containing a Highly Absorptive, Bay-Shaped Building Block for Effective NIR Photoacoustic Imaging

This study synthesizes a semiconducting polymer (SP) contrast agent named PY-DPP-δ by introducing a highly absorptive, bay-shaped Y5 analogue building block with extended conjugation and significant steric hindrance. PY-DPP-δ exhibits substantial absorption in the near-infrared (NIR) window and a considerable molecular backbone noncoplanarity (with a dihedral angle of 12.2°), leading to a robust twisted intramolecular charge transfer effect that can potentially boost the photoacoustic (PA) signal intensity. The PY-DPP-δ nanoparticles (PY-DPP-δ@NPs) demonstrate favorable biocompatibility and deliver high-performance in vivo PA imaging of subcutaneous vascular and tumor, as a 91.0-fold increase in PA signal intensity from blood vessels in the mouse ear and a 9.3-fold enhancement in the implanted tumor on the mouse back are recorded 60 min after the tail vein injections. This study presents a unique prospect to improve the design of SP contrast agents for better effectiveness in in vivo PA imaging within the NIR window.