NIR‐I Fluorescent Probes Based on Distyryl‐BODIPYs with Two‐Photon Excitation in NIR‐II Window**

Abstract Fluorescent dyes which exhibit emission/excitation in the second near‐infrared (NIR‐II, 1000–1350 nm) region are currently attracting significant attention in bioimaging and diagnostics applications. Furthermore, dyes with high two‐photon absorption cross‐section (TPA), such as BODIPY derivatives, are of a particular interest due to deeper signal penetration into biological tissues, better image contrast, reduced phototoxicity and photobleaching. Herein we report the synthesis and properties of new monomeric and dimeric di‐styryl‐BODIPY dyes, which have absorption maxima near 625 nm and emission in the range of 600–800 nm (NIR‐I, 650–950 nm). For the first time, we used a femtosecond Cr:Forsterite laser with a wavelength of 1250 nm (NIR‐II) for the excitation of NIR‐I di‐styryl‐BODIPY dyes by TPA. A cooperative effect was observed for TPA for the dimeric di‐styryl‐BODIPY dyes. The results obtained may be of great interest due to their potential applications in bioimaging and photodynamic therapy.