A BODIPY‐Based Donor/Donor–Acceptor System: Towards Highly Efficient Long‐Wavelength‐Excitable Near‐IR Polymer Dots with Narrow and Strong Absorption Features

Bright long-wavelength-excitable (green and beyond) semiconducting polymer dots (LWE-Pdots) are highly desirable for in vivo fluorescent imaging, as well as applications of multiple- wavelength-excitation based in vitro bioassays. Conventional LWE-Pdots have been obtained previously by incorporating a small amount of near-infrared (NIR) emitter into the backbone of a polymer host to develop a binary donor-acceptor (D-A) system. They usually suffer from severe concentration quenching and a trade-off between fluorescence quantum yield (Φ(f)) and absorption cross-section (σ), limiting the improvement in brightness. In this communication, we describe a ternary component (D(1)/D(2)-A) strategy to achieve ultrabright, green laser (532 nm)-excitable Pdots with narrow-band NIR emission by introducing a BODIPY-based assistant polymer donor as D(1). The novel use of BODIPY as predominant absorber in a Pdot allows strong, narrow-band absorption at 532 nm. The D(1)/D(2)-A Pdots possess simultaneously improved Φ(f) and σ compared to corresponding binary D(2)-A Pdots. Their Φ(f) is as high as 40.2%, one of the most efficient NIR Pdots reported. The ternary D(1)/D(2)-A Pdots show ultrahigh single-particle brightness, ~83 times brighter than Qdot 705 when excited by a 532 nm laser. Intravenously injected Pdots accumulate in implanted tumors in mice through the enhanced permeability and retention effect. Higher contrast in vivo tumor imaging was achieved using the ultrabright ternary Pdots versus the binary D-A Pdots. What’s more, this D(1)/D(2)-A design strategy supplies us a promising way to pursue ultrabright Pdots with even longer absorption and emission.