Discovery of BODIPY J-aggregates with absorption maxima beyond 1200 nm for biophotonics

Abstract

Organic dyes with absorption maxima in the second near-infrared window (NIR-II; 1000 to 1700 nm) are of great interest in biophotonics. However, because of the lack of appropriate molecular scaffolds, current research in this field is limited to cyanine dyes, and developing NIR-II–absorbing organic dyes for biophotonics remains an immense challenge. Here, we rationally designed an ethenylene-bridged BODIPY scaffold featuring excellent J-aggregation capabilities and revealed that the bridging ethylene unit is crucial for intermolecular J-coupling regulation. By integrating the electron-donating groups into the scaffold, we obtained a BODIPY dye, BisBDP2, with a J-aggregate absorption maximum of around 1300 nm. BisBDP2 J-aggregates show excellent photothermal performance, including intense photoacoustic response, and a high photothermal conversion efficiency value of 63%. In vivo results demonstrate the potential of J-aggregates for photoacoustic imaging and photothermal ablation of deep-seated tumors. This study will speed up the exploration of NIR-II–absorbing J-aggregates for future biophotonic applications.

Molecular Design of NIR-II Polymethine Fluorophores for Bioimaging and Biosensing

“…55 For many J-aggregates, bathochromic shifts beyond 100 nm are observed, attributed to excited states formed by extended domains of coherently coupled molecular transition dipoles. 56,57 The aggregation strength and hydrophobic effect of polymethine fluorophores depend on the size of their van der Waals surfaces and the freedom of torsional motions in the molecules. 47 Therefore, the long π-conjugation polymethine chain can inevitably accelerate the aggregation in polar solvents.…”

“…Since the 1930s, researchers have observed the phenomenon of J-aggregation with a narrow absorption band turning to a longer wavelength compared with the monomer absorption band and a nearly resonant fluorescence (tiny Stokes shift) with a narrow band . For many J-aggregates, bathochromic shifts beyond 100 nm are observed, attributed to excited states formed by extended domains of coherently coupled molecular transition dipoles. , The aggregation strength and hydrophobic effect of polymethine fluorophores depend on the size of their van der Waals surfaces and the freedom of torsional motions in the molecules . Therefore, the long π-conjugation polymethine chain can inevitably accelerate the aggregation in polar solvents.…”

Anti‐Quenching NIR‐II J‐Aggregates of Benzo[c]thiophene Fluorophore for Highly Efficient Bioimaging and Phototheranostics

“…used to develop efficient NIR-II emitters. [16][17][18][19][20] However, most reported fluorophores show H-type or disordered aggregation with weakened NIR absorption and fluorescence performance after forming NPs due to their rigid and planar molecular structures. [21][22][23] Only a few types of fluorophores possess J-type packing characteristics such as boron dipyrromethene (BODIPY), cyanine, squaraine, and perylene bisimide.…”

Bright, photostable, and long-circulating NIR-II nanoparticles for wholeprocess monitoring and evaluation of renal transplantation

“…Fluorescence imaging technology strongly relies on imaging contrast agents. In particular, organic luminogens with second near-infrared region (NIR-II, 1000-1700 nm) absorption and emission are highly desirable contrast agents due to their excellent biocompatibility, deep penetration depth and high imaging contrast (19,20,21). Although organic NIR-II luminogens have demonstrated their significant applications as fluorescent contrast agents, the commonly used commercial imaging contrast agents like ICG suffer the problem of concentration quenching effect, which means they can only be used in low concentration since high concentration will diminish and even quench the emission (22).…”