Non-Fused Conjugated Oligomer with Manipulated Intermolecular Charge Transfer for Highly Efficient Near-Infrared Phototheranostics of Cancer

Near-infrared (NIR) phototheranostics, combining photoacoustic imaging (PAI) and photothermal therapy (PTT), show great promise for cancer diagnosis and treatment. Organic molecules are excellent photothermal agents (PTAs) due to their strong NIR absorption and biodegradability. Typically, achieving good NIR response involves using fused-ring backbones, which require complex synthesis and yield lower production. In this work, 2F nanoparticles (NPs) are reported as an organic phototheranostic agent with high NIR responses, synthesized in just two simple steps with an 87% production yield for efficient PAI-guided PTT of cancer. Unlike traditional fused-ring structures, 2F is formed by joining donor and acceptor moieties with simple carbon–carbon bonds, simplifying synthesis and increasing yield. Although isolated 2F molecules have lower NIR absorption, forming NPs shifts the absorption peak from 708 to 808 nm, achieving NIR absorption comparable to state-of-the-art phototheranostics. This shift is due to significant charge transfer between dimers, forming a single-component charge-transfer complex with improved NIR absorption, as shown by absorption spectra and theoretical studies. Finally, 2F NPs demonstrate successful PAI-guided PTT of cancer under NIR excitation with strong anti-tumor performance. This work provides valuable insight into achieving both high synthesis yield and excellent photophysical performance in PTAs, advancing the development of PTT.